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Toward a Common Understanding of Diet–Exercise Strategies to Manipulate Fuel Availability for Training and Competition Preparation in Endurance Sport
Abstract
From the breakthrough studies of dietary carbohydrate and exercise capacity in the 1960s through to the more recent studies of cellular signaling and the adaptive response to exercise in muscle, it has become apparent that manipulations of dietary fat and carbohydrate within training phases, or in the immediate preparation for competition, can profoundly alter the availability and utilization of these major fuels and, subsequently, the performance of endurance sport (events >30 min up to ∼24 hr). A variety of terms have emerged to describe new or nuanced versions of such exercise-diet strategies (e.g., train low, train high, low-carbohydrate high-fat diet, periodized carbohydrate diet). However, the nonuniform meanings of these terms have caused confusion and miscommunication, both in the popular press and among the scientific community. Sports scientists will continue to hold different views on optimal protocols of fuel support for training and competition in different endurance events. However, to promote collaboration and shared discussions, a commonly accepted and consistent terminology will help to strengthen hypotheses and experimental/experiential data around various strategies. We propose a series of definitions and explanations as a starting point for a more unified dialogue around acute and chronic manipulations of fat and carbohydrate in the athlete's diet, noting philosophies of approaches rather than a single/definitive macronutrient prescription. We also summarize some of the key questions that need to be tackled to help produce greater insight into this exciting area of sports nutrition research and practice.
... VO 2peak that can be sustained for the event distance, and the oxygen (O 2 ) cost of movement (e.g., running/walking economy) [1][2][3][4][5]. Training and nutrition strategies for endurance performance aim to enhance various aspects of these characteristics [6], including ensuring that suitable substrates are able to fuel the event over its entire duration [4,7]. The economy of running or walking represents the relationship between oxygen utilisation and speed of locomotion [8], with a higher economy (lower oxygen cost for a given speed) at event-specific speeds being a better predictor of performance among a group of subelite/elite runners than . ...
... Indeed, as demonstrated more than a century ago [30,31], and explained by the stoichiometry of oxidative reactions [32], CHO oxidation produces 5-8% higher energy yield per litre of oxygen consumed through oxidative phosphorylation. Although contemporary sports nutrition guidelines for endurance performance already promote strategies to match CHO availability to the fuel demands of the event [7,33], it is worth considering whether further, even subtle, increases in CHO utilisation during the event might enhance economy in a meaningful way; either allowing the athlete to increase their speed for the same oxygen utilisation or reducing the oxygen and metabolic cost of a given speed. For example, according to our modelling [4], a 55 kg marathon runner with a sustainable . ...
... The chronic intervention associated with Carb Max, which increased total dietary CHO within daily energy intake, was likely associated with better restoration of daily muscle glycogen stores throughout the intensified training block [67]. Whether this supports better quality training, different physiological adaptations or different performance outcomes is beyond the scope of the current project and is a complex and nuanced issue [7]. Nevertheless, even if the acute CHO loading protocol alone achieved greater muscle glycogen storage prior to each of the MAX Trials A and C, this was not associated with a greater contribution of endogenous CHO stores to total CHO oxidation, at least during the second hour of the exercise protocol in which tracer methodology provides more credible data. ...
Given the importance of exercise economy to endurance performance, we implemented two strategies purported to reduce the oxygen cost of exercise within a 4 week training camp in 21 elite male race walkers. Fourteen athletes undertook a crossover investigation with beetroot juice (BRJ) or placebo (PLA) [2 d preload, 2 h pre-exercise + 35 min during exercise] during a 26 km race walking at speeds simulating competitive events. Separately, 19 athletes undertook a parallel group investigation of a multi-pronged strategy (MAX; n = 9) involving chronic (2 w high carbohydrate [CHO] diet + gut training) and acute (CHO loading + 90 g/h CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON; n = 10). There were no differences between BRJ and PLA trials for rates of CHO (p = 0.203) or fat (p = 0.818) oxidation or oxygen consumption (p = 0.090). Compared with CON, MAX was associated with higher rates of CHO oxidation during exercise, with increased exogenous CHO use (CON; peak = ~0.45 g/min; MAX: peak = ~1.45 g/min, p < 0.001). High rates of exogenous CHO use were achieved prior to gut training, without further improvement, suggesting that elite athletes already optimise intestinal CHO absorption via habitual practices. No differences in exercise economy were detected despite small differences in substrate use. Future studies should investigate the impact of these strategies on sub-elite athletes’ economy as well as the performance effects in elite groups.
... Carbohydrate availability can alter physiological and metabolic activity underpinning recovery outcomes, which includes training adaptations. 1 Muscle glycogen plays a key regulatory role for skeletal-muscle fuel utilization, enzyme activity, cellular signaling events, and gene expression. 2 Previously defined "train-low, compete-high" training protocols exploit these diverse roles by reducing carbohydrate availability during and (or) after training sessions that deplete muscle glycogen content (eg, approximately 2-h high-intensity interval training [HIIT]) to enhance training adaptations (eg, altered fuel kinetics during aerobic exercise, increase fat and reduced carbohydrate oxidation at relative exercise intensities) while maintaining high carbohydrate availability during competition. ...
... 2 Previously defined "train-low, compete-high" training protocols exploit these diverse roles by reducing carbohydrate availability during and (or) after training sessions that deplete muscle glycogen content (eg, approximately 2-h high-intensity interval training [HIIT]) to enhance training adaptations (eg, altered fuel kinetics during aerobic exercise, increase fat and reduced carbohydrate oxidation at relative exercise intensities) while maintaining high carbohydrate availability during competition. 1,3 When repeated over an extended training regimen, "train-low" protocols can increase mitochondrial enzyme activity and concentration and improve endurance performance through altered fuel kinetics, albeit in subelite athletes. 4 The compact "sleep-low train-low" model, which involves overnight restriction of carbohydrates after glycogen-depleting exercise, followed by a fasted training session the subsequent morning in a glycogen-depleted state, has been reported to stimulate adaptive metabolic responses to a greater degree to comparable exercise intensity with replete glycogen stores. ...
... Acute recovery outcomes assessed in the current study likely translate to elite-level cohorts, as they are in accordance with recovery nutrition guidelines and recommendation for the elite population. 1,12,35 Finally, the day before and morning of the exercise trial, meal provisions were matched for energy, macronutrients, water, and fiber (ie, participants were given the same pretrial control diet). Participants were instructed to "eat as much as tolerable," record intake (and any food wastage), and compliance was checked. ...
Purpose:
This study aimed to determine the effects of an acute "train-low" nutritional protocol on markers of recovery optimization compared to standard recovery nutrition protocol.
Methods:
After completing a 2-hour high-intensity interval running protocol, 8 male endurance athletes consumed a standard dairy milk recovery beverage (CHO; 1.2 g/kg body mass [BM] of carbohydrate and 0.4 g/kg BM of protein) and a low-carbohydrate (L-CHO; isovolumetric with 0.35 g/kg BM of carbohydrate and 0.5 g/kg BM of protein) dairy milk beverage in a double-blind randomized crossover design. Venous blood and breath samples, nude BM, body water, and gastrointestinal symptom measurements were collected preexercise and during recovery. Muscle biopsy was performed at 0 hour and 2 hours of recovery. Participants returned to the laboratory the following morning to measure energy substrate oxidation and perform a 1-hour distance test.
Results:
The exercise protocol resulted in depletion of muscle glycogen stores (250 mmol/kg dry weight) and mild body-water losses (BM loss = 1.8%). Neither recovery beverage replenished muscle glycogen stores (279 mmol/kg dry weight) or prevented a decrease in bacterially stimulated neutrophil function (-21%). Both recovery beverages increased phosphorylation of mTORSer2448 (main effect of time = P < .001) and returned hydration status to baseline. A greater fold increase in p-GSK-3βSer9/total-GSK-3β occurred on CHO (P = .012). Blood glucose (P = .005) and insulin (P = .012) responses were significantly greater on CHO (618 mmol/L per 2 h and 3507 μIU/mL per 2 h, respectively) compared to L-CHO (559 mmol/L per 2 h and 1147 μIU/mL per 2 h, respectively). Rates of total fat oxidation were greater on CHO, but performance was not affected.
Conclusion:
A lower-carbohydrate recovery beverage consumed after exercise in a "train-low" nutritional protocol does not negatively impact recovery optimization outcomes.
... This dietary strategy has in some cases been implemented by athletes [2,3], and may change substrate utilization (e.g., increase fat oxidation) [4], support endurance exercise training adaptations [5], and improve high-intensity exercise performance in sub-elite athletes [1]. One nutritional strategy that can be implemented to achieve a periodized carbohydrate intake is the administration of a non-ketogenic high-fat, low-carbohydrate diet (a restricted carbohydrate availability diet, which also retains sufficient carbohydrate to avoid sustained ketosis [6]) for a specified period of time for adapting to increased fat metabolism, followed by a short period of high carbohydrate intake (carbohydrate restoration; [6]). ...
... This dietary strategy has in some cases been implemented by athletes [2,3], and may change substrate utilization (e.g., increase fat oxidation) [4], support endurance exercise training adaptations [5], and improve high-intensity exercise performance in sub-elite athletes [1]. One nutritional strategy that can be implemented to achieve a periodized carbohydrate intake is the administration of a non-ketogenic high-fat, low-carbohydrate diet (a restricted carbohydrate availability diet, which also retains sufficient carbohydrate to avoid sustained ketosis [6]) for a specified period of time for adapting to increased fat metabolism, followed by a short period of high carbohydrate intake (carbohydrate restoration; [6]). ...
... Over the past twenty years, short-term fat-adaptation/carbohydrate restoration (FACR) diets have been investigated, and typically encompass at least five days of 15-20% energy intake from carbohydrate, and 60-65% energy from fat, followed by 24 h of a high-carbohydrate diet (10-12 g/kg per day; [6]). Reported effects of FACR interventions include an increased contribution of fat as a substrate for exercise performance, via increased rates of whole-body fat oxidation [5], and increases in intra-muscular triglyceride stores, fatty acid mobilization, and transport. ...
Periodized carbohydrate availability can enhance exercise capacity, but the effects of short-term fat adaptation carbohydrate restoration (FACR) diets on metabolic responses and exercise performance in endurance athletes have not been conclusively determined. This study aimed to investigate the effect of a FACR diet on measures of resting metabolism, exercise metabolism, and exercise performance. Well-trained male runners (n = 8) completed a FACR dietary intervention (five days’ carbohydrate < 20% and fat > 60% energy, plus one-day carbohydrate ≥ 70% energy), and a control high-carbohydrate (HCHO) diet for six days (carbohydrate > 60% energy; fat < 20% energy) in a randomized crossover design. Pre- and post-intervention metabolic measures included resting metabolic rate (RMR), respiratory quotient (RQ), maximum fat oxidation rate during exercise (MFO), and maximum fat oxidation intensity (FATmax). Measures of exercise performance included maximal oxygen uptake (VO2max), running economy (RE), and 5 km running time trial (5 km-TT). In FACR compared with HCHO, there were significant improvements in FATmax (p = 0.006) and RE (p = 0.048). There were no significant differences (p > 0.05) between FACR and HCHO in RMR, RQ, VO2max, or 5 km-TT. Findings suggest that a short-term (six days) FACR diet may facilitate increased fat oxidation and submaximal exercise economy but does not improve 5 km-TT performance.
... Carbohydrate (CHO) availability has emerged as another key theme of interest, with this term describing the balance between CHO requirements of the muscle and central nervous system (and potentially other organs and body systems) around an exercise session relative to the endogenous and/or endogenous CHO supply [8]. There is plentiful evidence that strategies which achieve high CHO availability (i.e., to balance supply to the demand) are associated with enhancement of exercise capacity and sports performance, particularly during prolonged endurance events requiring high intensity efforts [9,10]. ...
... There is plentiful evidence that strategies which achieve high CHO availability (i.e., to balance supply to the demand) are associated with enhancement of exercise capacity and sports performance, particularly during prolonged endurance events requiring high intensity efforts [9,10]. These outcomes have led to recommendations that when optimal performance is desired, endurance athletes adopt strategies of daily CHO intake and/or high CHO availability around key exercise sessions to meet the session fuel demands [8]. However, the application of advanced analytical techniques to investigate exercise-nutrient interactions has shown strategies that achieve low CHO availability (i.e., acute CHO restriction around an exercise session) can amplify cellular adaptations within skeletal muscle during and after exercise [11]. ...
... However, the application of advanced analytical techniques to investigate exercise-nutrient interactions has shown strategies that achieve low CHO availability (i.e., acute CHO restriction around an exercise session) can amplify cellular adaptations within skeletal muscle during and after exercise [11]. If manipulation of CHO availability could be integrated into the training cycle, matching availability to the demands and goals of each session, a strategic blend of augmented adaptation workouts and targeted quality sessions could lead to enhanced performance outcomes [8,12]. Meanwhile, an alternative approach to metabolic preparation for endurance exercise is to chronically restrict dietary CHO, allowing the muscle to achieve a 2-3 fold increase in fat oxidation, coupled with a simultaneous decrease in CHO utilization, thus shifting its fuel reliance from finite CHO stores to the relatively unlimited body fat reserves [13][14][15]. ...
The provision or restriction of select nutrients in an athlete’s diet can elicit a variety of changes in fuel utilization, training adaptation, and performance outcomes. Furthermore, nutrient availability can also influence athlete health, with one key system of interest being iron metabolism. The aim of this review was to synthesize the current evidence examining the impact of dietary manipulations on the iron regulatory response to exercise. Specifically, we assessed the impact of both acute and chronic carbohydrate (CHO) restriction on iron metabolism, with relevance to contemporary sports nutrition approaches, including models of periodized CHO availability and ketogenic low CHO high fat diets. Additionally, we reviewed the current evidence linking poor iron status and altered hepcidin activity with low energy availability in athletes. A cohesive understanding of these interactions guides nutritional recommendations for athletes struggling to maintain healthy iron stores, and highlights future directions and knowledge gaps specific to elite athletes.
... adaptation to a LCHF diet during a period of intensified training on exercise metabolism and performance of world-class race walkers [4], comparing it with an energy-matched diet providing high CHO availability around all training sessions (HCHO). A third option achieved periodisation of CHO availability (PCHO) with some training sessions being undertaken with high CHO intake to support training quality while others were undertaken with low CHO availability to enhance metabolic adaptation to the training stimulus [18]. This represents the modern approach of periodisation and personalisation of sports nutrition in which CHO availability is manipulated within and between days so that each exercise session can be undertaken with a dietary strategy that best supports the goals and characteristics of the workout [18]. ...
... A third option achieved periodisation of CHO availability (PCHO) with some training sessions being undertaken with high CHO intake to support training quality while others were undertaken with low CHO availability to enhance metabolic adaptation to the training stimulus [18]. This represents the modern approach of periodisation and personalisation of sports nutrition in which CHO availability is manipulated within and between days so that each exercise session can be undertaken with a dietary strategy that best supports the goals and characteristics of the workout [18]. Each walker was allocated to a dietary treatment according to their belief effect in the benefits of the intervention. ...
... Which sporting events meet such a categorisation is a topic of debate [46,74], but should also consider the characteristics of the individual athlete and their responsiveness to and tolerance of the LCHF diet, since this is known to be variable [25,27,61]. Alternatively, strategies that try to periodise the exposure to high CHO availability against the background of superior capacity for fat oxidation have been proposed as a method to reduce the limitations of fat as an exercise substrate [18]. Our present study tested the anecdotal proposition that prior exposure to the LCHF diet acts like altitude training in leaving a legacy of physiological adaptations that would integrate with restoration of high CHO availability and a taper to produce superior race performance. ...
Introduction:
We repeated our study of intensified training on a ketogenic low-carbohydrate (CHO), high-fat diet (LCHF) in world-class endurance athletes, with further investigation of a "carryover" effect on performance after restoring CHO availability in comparison to high or periodised CHO diets.
Methods:
After Baseline testing (10,000 m IAAF-sanctioned race, aerobic capacity and submaximal walking economy) elite male and female race walkers undertook 25 d supervised training and repeat testing (Adapt) on energy-matched diets: High CHO availability (8.6 g∙kg-1∙d-1 CHO, 2.1 g∙kg-1∙d-1 protein; 1.2 g∙kg-1∙d-1 fat) including CHO before/during/after workouts (HCHO, n = 8): similar macronutrient intake periodised within/between days to manipulate low and high CHO availability at various workouts (PCHO, n = 8); and LCHF (<50 g∙d-1 CHO; 78% energy as fat; 2.1 g∙kg-1∙d-1 protein; n = 10). After Adapt, all athletes resumed HCHO for 2.5 wk before a cohort (n = 19) completed a 20 km race.
Results:
All groups increased VO2peak (ml∙kg-1∙min-1) at Adapt (p = 0.02, 95%CI: [0.35-2.74]). LCHF markedly increased whole-body fat oxidation (from 0.6 g∙min-1 to 1.3 g∙min-1), but also the oxygen cost of walking at race-relevant velocities. Differences in 10,000 m performance were clear and meaningful: HCHO improved by 4.8% or 134 s (95% CI: [207 to 62 s]; p < 0.001), with a trend for a faster time (2.2%, 61 s [-18 to +144 s]; p = 0.09) in PCHO. LCHF were slower by 2.3%, -86 s ([-18 to -144 s]; p < 0.001), with no evidence of superior "rebound" performance over 20 km after 2.5 wk of HCHO restoration and taper.
Conclusion:
Our previous findings of impaired exercise economy and performance of sustained high-intensity race walking following keto-adaptation in elite competitors were repeated. Furthermore, there was no detectable benefit from undertaking an LCHF intervention as a periodised strategy before a 2.5-wk race preparation/taper with high CHO availability.
Trial registration:
Australia New Zealand Clinical Trial Registry: ACTRN12619000794101.
... The performance of sport and other physical activities, particularly those involving prolonged submaximal or intermittent highintensity exercise, is impaired by low carbohydrate (CHO) availability (Karelis et al., 2010), which is defined as an insufficient glycogen concentration and inadequate blood glucose (BG) supply in comparison with the fuel needs of an exercise session (Burke, Hawley, et al., 2018;Impey et al., 2018). Targets for CHO intake, to optimize performance and support health and well-being, in the everyday diet and during competition are a prominent feature of sports nutrition guidelines (Thomas, Erdman, et al., 2016). ...
... Targets for CHO intake, to optimize performance and support health and well-being, in the everyday diet and during competition are a prominent feature of sports nutrition guidelines (Thomas, Erdman, et al., 2016). The evolution of these guidelines has included the concept of specificity to the athlete and to the exercise scenario (personalization) and differences in intake between and within days according to the fuel requirements and goals of each session of exercise (periodization; Burke, Hawley, et al., 2018;Impey et al., 2018). More recently, sports nutrition guidelines have incorporated recommendations relating to energy availability (EA), matching energy intake (EI) according to the energy demands of exercise to ensure that body metabolism and function are optimized (Mountjoy et al., 2018). ...
This review discusses the potential value of tracking interstitial glucose with continuous glucose monitors (CGMs) in athletes, highlighting possible applications and important considerations in the collection and interpretation of interstitial glucose data. CGMs are sensors that provide real time, longitudinal tracking of interstitial glucose with a range of commercial monitors currently available. Recent advancements in CGM technology have led to the development of athlete-specific devices targeting glucose monitoring in sport. Although largely untested, the capacity of CGMs to capture the duration, magnitude, and frequency of interstitial glucose fluctuations every 1–15 min may present a unique opportunity to monitor fueling adequacy around competitive events and training sessions, with applications for applied research and sports nutrition practice. Indeed, manufacturers of athlete-specific devices market these products as a “fueling gauge,” enabling athletes to “push their limits longer and get bigger gains.” However, as glucose homeostasis is a complex phenomenon, extensive research is required to ascertain whether systemic glucose availability (estimated by CGM-derived interstitial glucose) has any meaning in relation to the intended purposes in sport. Whether CGMs will provide reliable and accurate information and enhance sports nutrition knowledge and practice is currently untested. Caveats around the use of CGMs include technical issues (dislodging of sensors during periods of surveillance, loss of data due to synchronization issues), practical issues (potential bans on their use in some sporting scenarios, expense), and challenges to the underpinning principles of data interpretation, which highlight the role of sports nutrition professionals to provide context and interpretation.
... From a practical perspective, this so-called "trainlow" paradigm has been translated as "fuelling for the work required" whereby daily CHO intake is adjusted day-by-day and meal-by-meal according to the upcoming activity and the desired outcome of the exercise session i.e., promoting exercise intensity versus stimulating metabolic adaptations (Impey et al., 2018). Although such models of nutritional periodization are gaining increased recognition amongst endurance sports (Burke et al., 2018;Impey et al., 2018;Stellingwerff et al., 2019), no such models have yet been developed for the professional soccer player. ...
... Nonetheless, we previously observed that commencing high-intensity intermittent running (using a model aligned to the training-intensities associated with small sided games, i.e., 6 × 3 min bouts of running completed at 85-90% VO 2max ) with reduced pre-exercise muscle glycogen (and without provision of CHO during exercise) augments training-induced up-regulation of oxidative enzyme activity in both the gastrocnemius and vastus lateralis muscle, as compared with conditions considered of normal pre-exercise muscle glycogen and consumption of CHO during training (Morton et al., 2009). It should also be noted, however, that many of the previous models of CHO periodization studied within the literature have incorporated models of CHO restriction that may not always be practically applicable to the professional player, e.g., training twice per day with limited recovery between sessions, training late in the evening followed by a fasted training session on the subsequent morning (the so-called sleep-low train-low model) etc. (see Impey et al., 2018;Burke et al., 2018 for a detailed discussion of such models). ...
Despite more than four decades of research examining the physical demands of match-play, quantification of the customary training loads of adult male professional soccer players is comparatively recent. The training loads experienced by players during weekly micro-cycles are influenced by phase of season, player position, frequency of games, player starting status, player-specific training goals and club coaching philosophy. From a macronutrient perspective, the periodization of physical loading within (i.e., match versus training days) and between contrasting micro-cycles (e.g., 1, 2 or 3 games per week schedules) has implications for daily carbohydrate (CHO) requirements. Indeed, aside from the well-recognised role of muscle glycogen as the predominant energy source during match-play, it is now recognised that the glycogen granule may exert regulatory roles in activating or attenuating the molecular machinery that modulate skeletal muscle adaptations to training. With this in mind, the concept of CHO periodization is gaining in popularity, whereby CHO intake is adjusted day-by-day and meal-by-meal according to the fuelling demands and specific goals of the upcoming session. On this basis, the present paper provides a contemporary overview and theoretical framework for which to periodize CHO availability for the professional soccer player according to the "fuel for the work" paradigm.
... La prueba se caracteriza por la dificultad técnica que presentan las distintas zonas del circuito. La organización de la prueba solo presenta un avituallamiento en la línea de meta, por lo que la realización de un plan dietético-nutricional individualizado se hace imprescindible para garantizar el aporte de energía, la hidratación y el rendimiento, tratando de evitar la aparición de posibles efectos adversos (Burke et al., 2018). El objetivo principal de este estudio es realizar una planificación dietético-nutricional de un ciclista de mountain bike para afrontar una carrera de cross country y mejorar la composición corporal. ...
... En el periodo de 3 semanas previas a la prueba, en nuestra intervención nos decantamos por una estrategia donde se priorizara una alta ingesta de HC (>6 g/ kg/día) para el menú junto a los requerimientos durante y posterior al ejercicio y 7 g/kg/día para la dieta de carga) (Burke et al., 2018;Mata et al., 2019). El protocolo de carga se evaluó en esta fase para comprobar si era adecuado tanto a las preferencias como a la tolerancia del ciclista. ...
El cross country es una modalidad del ciclismo de mountain bike (MTB), cuyas competiciones se caracterizan por dar un determinado número de vueltas a un circuito con una distancia desde 6-9km hasta 40-200km. En estos eventos, es importante planificar una estrategia dietético-nutricional para mitigar la aparición de resultados adversos relacionados con la nutrición. El objetivo de este estudio fue realizar la planificación dietético-nutricional de un ciclista de MTB que disputa una competición de cross country. El ciclista es un varón de 27 años (VO2max=74.46 ml•kg-1•min-1; PAM=420W; altura=1.81m; peso=78.6kg; % masa grasa=9.47, sumatorio de pliegues=61.9mm) con 3 años de experiencia en el entrenamiento y competición de pruebas MTB a nivel regional. La intervención tuvo lugar en el gabinete Alinua de la Universidad de Alicante, cuya finalidad fue mejorar la composición corporal y elaborar una programación dietético-nutricional para disputar una carrera de MTB el 23-2-2020 en la provincia de Alicante. La intervención incluía las recomendaciones para deportistas de resistencia y se dividió en un periodo de preparación, periodo de 3 semanas previas a la carrera y periodo competitivo. El participante realizó satisfactoriamente la prueba, se adhirió a la planificación, y no manifestó ningún problema. Para un ciclista, afrontar un evento de estas características con éxito requiere de un asesoramiento teórico-práctico y una programación dietético-nutricional de manera individualizada que trate de contribuir nutricionalmente antes, durante y después de la práctica del ejercicio, así como aminorar la posible aparición de contratiempos que puedan poner en riesgo el rendimiento y la salud. Abstract. Cross Country is a modality of mountain bike cycling (MTB), whose competitions are characterized by giving a certain number of laps to a circuit with a distance from 6-9km to 40-200km. In these events, it is important to plan a dietetic-nutritional strategy to mitigate the appearance of nutrition-related adverse outcomes. The purpose of the study was to plan the dietetic-nutritional planning of a MTB cyclist who competes in a Cross Country competition. The cyclist is a 27-year-old male (VO2max=74.46 ml•kg-1•min-1; MAP=420W; height=1.81m; weight=78.6kg; % fat mass=9.47; sum of 8 skinfolds=61.9mm) with 3 years of experience in training and competing in MTB events at a regional level. The intervention took place in the Alinua cabinet of the University of Alicante, whose purpose was to improve the body composition and to elaborate a dietetic-nutritional program to dispute a MTB race on 23-2-2020 in the province of Alicante. The intervention included the recommendations for endurance athletes and was divided into a preparation period, a period of 3 weeks before the race and a competitive period. Finally, the participant successfully completed the race according to the planning and did not manifest any problems. For a cyclist, facing an event of these characteristics successfully requires theoretical-practical advice and dietary-nutritional programming in an individualized way that tries to contribute at a nutritional level before, during and after physical exercise, as well as to reduce the possible appearance of setbacks that may jeopardize performance and health.
... While adherence to a LCHF diet aims to change the substrate utilization and increase the reliance on fat during exercise, a different nutritional approach including periodic CHO restriction has emerged as a promising way to amplify the acute response to endurance training [19]. It is well-established that endurance training leads to the creation of new mitochondrial reticular components (i.e., mitochondrial biogenesis) [20]. ...
... Since the pioneering study by Hansen et al. from 2004 [36], several different approaches to manipulate the CHO availability during training and recovery have been presented [32], which has led to both confusion and miscommunication in the elite sport community about the variety of terms related to CHO manipulation. Accordingly, this recently gave rise the proposal of a set of definitions by Burke and colleagues, attempting to create a common understanding of diet-exercise strategies [19]. Despite their different nuances, studies in the existing literature can be divided into the following: 1) "Twice-a-day training" that involves a training session designed to deplete muscle glycogen, followed by recovery with CHO restriction or fasting and a second training session commenced with low muscle glycogen levels, 2) "Sleep low" which refers to a glycogen-depleting session of training followed by overnight CHO restriction or fasting followed by a training session in the morning, 3) "Fasted training" by conduction of endurance training without CHO provision or 4) "Recover low" with a single glycogen-depleting training session followed by recovery with CHO restriction or fasting. ...
Endurance athletes typically consume carbohydrate-rich diets to allow for optimal performance during competitions and intense training. However, acute exercise studies have revealed that training or recovery with low muscle glycogen stimulates factors of importance for mitochondrial biogenesis in addition to favourable metabolic adaptations in trained athletes. Compromised training quality and particularly lower intensities in peak intervals seem to be a major drawback from dietary interventions with chronic carbohydrate (CHO) restriction. Therefore, the concept of undertaking only selected training sessions with restricted CHO availability (periodized CHO restriction) has been proposed for endurance athletes. However, the overall performance effect of this concept has not been systematically reviewed in highly adapted endurance-trained athletes. We therefore conducted a meta-analysis of training studies that fulfilled the following criteria: a) inclusion of females and males demonstrating a VO 2 max ≥ 55 and 60 ml · kg − 1 · min − 1 , respectively; b) total intervention and training periods ≥ 1 week, c) use of interventions including training and/or recovery with periodized carbohydrate restriction at least three times per week, and d) measurements of endurance performance before and after the training period. The literature search resulted in 407 papers of which nine studies fulfilled the inclusion criteria. The subsequent meta-analysis demonstrated no overall effect of CHO periodization on endurance performance compared to control endurance training with normal (high) CHO availability (standardized mean difference = 0.17 [− 0.15, 0.49]; P = 0.29). Based on the available literature, we therefore conclude that periodized CHO restriction does not per se enhance performance in endurance-trained athletes. The review discusses different approaches to CHO periodization across studies with a focus on identifying potential physiological benefits.
... Many players associated high carbohydrate intakes with increased fat mass. The challenges of changing perceptions and misconceptions with regards to the amount of carbohydrate required for team sports players has been highlighted in past research [8,22,23]. International carbohydrate recommendations have evolved in recent times, with greater focus on carbohydrate periodization strategies that focus on the timing and manipulation of carbohydrate intake [23]. Manipulating dietary carbohydrate intake to align with training outputs can be a sustainable practice to adjust body composition and enhance training adaptions [22]. ...
... The challenges of changing perceptions and misconceptions with regards to the amount of carbohydrate required for team sports players has been highlighted in past research [8,22,23]. International carbohydrate recommendations have evolved in recent times, with greater focus on carbohydrate periodization strategies that focus on the timing and manipulation of carbohydrate intake [23]. Manipulating dietary carbohydrate intake to align with training outputs can be a sustainable practice to adjust body composition and enhance training adaptions [22]. ...
(1) Background: Many professional Australian Football (AF) players do not meet recommended sports nutrition guidelines despite having access to nutrition advice. There are a range of factors that can influence players′ ability to meet their nutrition goals and awareness of the barriers players face is essential to ensure that dietary advice translates into practice. Therefore, this qualitative research study aimed to explore the factors influencing AF players’ dietary intakes and food choice. (2) Methods: Semi-structured interviews were conducted with twelve professional male AF players. (3) Results: Less experienced players restricted their carbohydrate intake to meet body composition goals, particularly during preseason and surrounding body composition assessment. During the competition season players had a greater focus on performance and placed more emphasis on carbohydrate intake in the lead up to matches. Players felt nutrition goals were easier to achieve when dietary choices were supported by their families and peers. One-on-one consultations provided by a sports dietitian were players′ preferred mode of nutrition intervention. Individualized nutrition advice is required for less experienced AF players who may be vulnerable to unsustainable dietary habits. Experienced AF players can support junior teammates by promoting positive team culture related to body composition, nutrition and performance.
... However, given the ergogenic effects of CHO on exercise performance (Hawley et al. 1997;Stellingwerff & Cox, 2014), such an approach often contrasts with the nutritional practices adopted by athletic populations. Indeed, athletes will increase CHO availability in the day(s) and hours before competition so as to commence exercise with sufficient muscle and liver glycogen stores (Burke et al. 2018). In addition, it is now an established practice for elite endurance athletes to also consume CHO during exercise, with contemporary guidelines recommending CHO ingestion rates up to 90 gh −1 when exercise is greater than 2.5-3 h in duration (Thomas et al. 2016). ...
... We employed an experimental design that evaluated muscle fuel selection in a manner that is aligned with the nutritional practices often adopted by endurance athletes, i.e. CHO availability was increased in the day(s) and hours before competition so as to commence exercise with sufficient muscle and liver glycogen stores (Burke et al. 2018). In accordance with the trained status of our participants and the 36 h CHO loading protocol, our model was successful in achieving highly elevated pre-exercise glycogen stores, as evidenced by whole muscle glycogen concentrations (see Fig. 3) and the dark PAS staining in both type I and type II muscle fibres (see Fig. 10). ...
Key points:
Muscle glycogen and intramuscular triglycerides (IMTG, stored in lipid droplets) are important energy substrates during prolonged exercise. Exercise-induced changes in lipid droplet (LD) morphology (i.e., LD size and number) has not yet been studied under nutritional conditions typically adopted by elite endurance athletes, that is, after carbohydrate (CHO) loading and CHO feeding during exercise. We report for the first time that exercise reduces IMTG content in both central and peripheral regions of type I and IIa fibres, reflective of decreased LD number in both fibre types whereas reductions in LD size was exclusive to type I fibres. Additionally, CHO feeding does not alter subcellular IMTG utilisation, LD morphology or muscle glycogen utilisation in type I or IIa/II fibres. In the absence of alterations to muscle fuel selection, CHO feeding does not attenuate cell signalling with regulatory roles in mitochondrial biogenesis.
Abstract:
We examined the effects of carbohydrate (CHO) feeding on lipid droplet (LD) morphology, muscle glycogen utilisation and exercise-induced skeletal muscle cell signalling. After a 36 h CHO loading protocol and pre-exercise meal (12 and 2 g·kg-1 , respectively), eight trained males ingested 0, 45 or 90 g CHO·h-1 during 180 min cycling at lactate threshold followed by an exercise capacity test (150% lactate threshold). Muscle biopsies were obtained pre- and post-completion of submaximal exercise. Exercise decreased (P<0.01) glycogen concentration to comparable levels (∼700 to 250 mmol·kg-1 dw), though utilisation was greater in type I (∼40%) versus type II fibres (∼10%) (P<0.01). LD content decreased in type I (∼50%) and type IIa fibres (∼30%) (P<0.01) with greater utilisation in type I fibres (P<0.01). CHO feeding did not affect glycogen or IMTG utilisation in type I or II fibres (all P>0.05). Exercise decreased LD number within central and peripheral regions of both type I and IIa fibres, though reduced LD size was exclusive to type I fibres. Exercise induced (all P<0.05) comparable AMPKThr172 (∼4 fold), p53Ser15 (∼2 fold) and CaMKIIThr268 phosphorylation (∼2 fold) with no effects of CHO feeding (all P>0.05). CHO increased exercise capacity where 90 g·h-1 (233 ± 133 s) > 45 g·h-1 (156 ± 66 s; P = 0.06) > 0 g·h-1 (108 ± 54 s; P = 0.03). In conditions of high pre-exercise CHO availability, we conclude CHO feeding does not influence exercise-induced changes in LD morphology, glycogen utilisation or cell signalling pathways with regulatory roles in mitochondrial biogenesis. This article is protected by copyright. All rights reserved.
... Broadly, two iterations of LCHF dietary approaches existketogenic (providing < 5% of energy intake from carbohydrate) and non-ketogenic (providing~15-20% of energy intake from carbohydrate) [5]. A nonketogenic LCHF diet can be used as part of a nutritionally periodized dietary plan featuring periods of reduced carbohydrate intake in order to maximize fat-burning adaptations [5]. ...
... Broadly, two iterations of LCHF dietary approaches existketogenic (providing < 5% of energy intake from carbohydrate) and non-ketogenic (providing~15-20% of energy intake from carbohydrate) [5]. A nonketogenic LCHF diet can be used as part of a nutritionally periodized dietary plan featuring periods of reduced carbohydrate intake in order to maximize fat-burning adaptations [5]. Approximately 20% of endurance athletes follow a LCHF or periodized carbohydrate dietary pattern, the majority of whom also perform fastedstate training related to a desire to increase fat oxidation during exercise [6]. ...
Background
Swimming economy refers to the rate of energy expenditure relative to swimming speed of movement, is inversely related to the energetic cost of swimming, and is as a key factor influencing endurance swimming performance. The objective of this study was to determine if high-carbohydrate, low-fat (HCLF) and low-carbohydrate, high-fat (LCHF) diets affect energetic cost of submaximal swimming.
Methods
Eight recreational swimmers consumed two 3-day isoenergetic diets in a crossover design. Diets were tailored to individual food preferences, and macronutrient consumption was 69–16-16% and 16–67-18% carbohydrate-fat-protein for the HCLF and LCHF diets, respectively. Following each 3-day dietary intervention, participants swam in a flume at velocities associated with 50, 60, and 70% of their maximal aerobic capacity (VO 2max ). Expired breath was collected and analyzed while they swam which enabled calculation of the energetic cost of swimming. A paired t-test compared macronutrient distribution between HCLF and LCHF diets, while repeated-measures ANOVA determined effects of diet and exercise intensity on physiological endpoints.
Results
Respiratory exchange ratio was significantly higher in HCLF compared to LCHF ( p = 0.003), but there were no significant differences in the rate of oxygen consumption ( p = 0.499) or energetic cost of swimming ( p = 0.324) between diets. Heart rate did not differ between diets ( p = 0.712), but oxygen pulse, a non-invasive surrogate for stroke volume, was greater following the HCLF diet ( p = 0.029).
Conclusions
A 3-day high-carbohydrate diet increased carbohydrate utilization but did not affect swimming economy at 50–70% VO 2max . As these intensities are applicable to ultramarathon swims, future studies should use higher intensities that would be more relevant to shorter duration events.
... Broadly, two iterations of LCHF dietary approaches exist -ketogenic (providing <5% of energy intake from carbohydrate) and non-ketogenic (providing ~15-20% of energy intake from carbohydrate) (5). A non-ketogenic LCHF diet can be used as part of a nutritionally periodized dietary plan featuring periods of reduced carbohydrate intake in order to maximize fat-burning adaptations (5). ...
... Broadly, two iterations of LCHF dietary approaches exist -ketogenic (providing <5% of energy intake from carbohydrate) and non-ketogenic (providing ~15-20% of energy intake from carbohydrate) (5). A non-ketogenic LCHF diet can be used as part of a nutritionally periodized dietary plan featuring periods of reduced carbohydrate intake in order to maximize fat-burning adaptations (5). Approximately 20% of endurance athletes follow a LCHF or periodized carbohydrate dietary pattern, the majority of whom also perform fasted-state training related to a desire to increase fat oxidation during exercise (6). ...
Background: Swimming economy refers to the rate of energy expenditure relative to swimming speed of movement, is inversely related to the energetic cost of swimming, and is as a key factor influencing endurance swimming performance. The objective of this study was to determine if high-carbohydrate, low-fat (HCLF) and low-carbohydrate, high-fat (LCHF) diets affect energetic cost of submaximal swimming.
Methods: Eight recreational swimmers consumed two 3-day isoenergetic diets in a crossover design. Diets were tailored to individual food preferences, and macronutrient consumption was 69-16-16% and 16-67-18% carbohydrate-fat-protein for the HCLF and LCHF diets, respectively. Following each 3-day dietary intervention, participants swam in a flume at velocities associated with 50, 60, and 70% of their maximal aerobic capacity (VO2max). Expired breath was collected and analyzed while they swam which enabled calculation of the energetic cost of swimming. A paired t-test compared macronutrient distribution between HCLF and LCHF diets, while repeated-measures ANOVA determined effects of diet and exercise intensity on physiological endpoints.
Results: Respiratory exchange ratio was significantly higher in HCLF compared to LCHF (p = 0.003), but there were no significant differences in the rate of oxygen consumption (p = 0.499) or energetic cost of swimming (p = 0.324) between diets. Heart rate did not differ between diets (p = 0.712), but oxygen pulse, a non-invasive surrogate for stroke volume, was greater following the HCLF diet (p = 0.029).
Conclusions: A 3-day high-carbohydrate diet increased carbohydrate utilization but did not affect swimming economy at 50-70% VO2max. As these intensities are applicable to ultramarathon swims, future studies should use higher intensities that would be more relevant to shorter duration events.
... The concept of deliberately commencing endurance exercise with reduced muscle glycogen (i.e. the train-low paradigm, Burke et al., 2018) is now recognised as a potent nutritional strategy that is able to modulate acute skeletal muscle cell signalling Wojtaszewski et al., 2003;Yeo et al., 2010) and transcriptional responses Pilegaard et al., 2002;Psilander, Frank, Flockhart, & Sahlin, 2013). Furthermore, repeated bouts of train-low exercise can subsequently augment many hallmark muscle adaptations inherent to the endurance phenotype. ...
... performance (Marquet et al., 2016a(Marquet et al., , 2016b. As such, the train-low paradigm and wider CHO periodisation strategies have subsequently gained increased recognition amongst athletic populations (Burke et al., 2018;Impey et al., 2018;Stellingwerff, 2012). ...
New findings:
What is the central question of this study? What is the absolute level of pre-exercise glycogen concentration required to augment the exercise-induced signalling response regulating mitochondrial biogenesis? What is the main finding and its importance? Commencing high-intensity endurance exercise with reduced pre-exercise muscle glycogen concentrations confers no additional benefit to the early signalling responses that regulate mitochondrial biogenesis.
Abstract:
We examined the effects of graded muscle glycogen on the subcellular location of AMPK and PGC-1α protein content and mRNA expression of genes associated with the regulation of mitochondrial biogenesis and substrate utilisation in human skeletal muscle. In a repeated measures design, eight trained male cyclists completed acute high-intensity interval (HIT) cycling (8 × 5 min at 80% peak power output) with graded concentrations of pre-exercise muscle glycogen. Following initial glycogen depleting exercise, subjects ingested 2 g kg-1 (L-CHO), 6 g kg-1 (M-CHO) or 14 g kg-1 (H-CHO) of carbohydrate during a 36 h period, such that exercise was commenced with graded (P < 0.05) muscle glycogen concentrations (H-CHO; 531 ± 83, M-CHO; 332 ± 88, L-CHO; 208 ± 79 mmol·kg-1 dw). Exercise depleted muscle glycogen to < 300 mmol·kg-1 dw in all trials (H-CHO; 270 ± 88, M-CHO; 173 ± 74, L-CHO; 100 ± 42 mmol·kg-1 dw) and induced comparable increases in nuclear AMPK protein content (∼2 fold) and PGC-1α (∼5 fold), p53 (∼1.5 fold) and CPT-1 (∼2 fold) mRNA between trials (all P < 0.05). The magnitude of increase in PGC-1α mRNA was also positively correlated with post-exercise glycogen concentration (P < 0.05). In contrast, exercise nor carbohydrate availability affected the subcellular location of PGC-1α protein or PPAR, SCO2, SIRT1, DRP1, MFN2 or CD36 mRNA. Using a sleep-low, train-low model with a high-intensity endurance exercise stimulus, we conclude that pre-exercise muscle glycogen does not modulate skeletal muscle cell signalling. This article is protected by copyright. All rights reserved.
... Storage of glycogen is associated with a gain in body mass, which may be detrimental to performance in weight-bearing sports 1 . Thus, manipulation of pre-exercise skeletal muscle glycogen content could be a strategy to optimize body mass prior to competition, provided that glycogen depletion does not become limiting for performance. ...
Performance in short-duration sports is highly dependent on muscle glycogen, but the total degradation is only moderate and considering the water-binding property of glycogen, unnecessary storing of glycogen may cause an unfavorable increase in body mass. To investigate this, we determined the effect of manipulating dietary carbohydrates (CHO) on muscle glycogen content, body mass and short-term exercise performance. In a cross-over design twenty-two men completed two maximal cycle tests of either 1-min (n = 10) or 15-min (n = 12) duration with different pre-exercise muscle glycogen levels. Glycogen manipulation was initiated three days prior to the tests by exercise-induced glycogen-depletion followed by ingestion of a moderate (M-CHO) or high (H-CHO) CHO-diet. Subjects were weighed before each test, and muscle glycogen content was determined in biopsies from m. vastus lateralis before and after each test. Pre-exercise muscle glycogen content was lower following M-CHO than H-CHO (367 mmol · kg-1 DW vs. 525 mmol · kg-1 DW, P < 0.00001), accompanied by a 0.7 kg lower body mass (P < 0.00001). No differences were observed in performance between diets in neither the 1-min (P = 0.33) nor the 15-min (P = 0.99) test. In conclusion, pre-exercise muscle glycogen content and body mass was lower after ingesting moderate compared with high amounts of CHO, while short-term exercise performance was unaffected. This demonstrates that adjusting pre-exercise glycogen levels to the requirements of competition may provide an attractive weight management strategy in weight-bearing sports, particularly in athletes with high resting glycogen levels.
... However, it was only at the Montreal Olympic Games in 1976 that an appreciation of the importance of dietary carbohydrates among athletes and coaches started to emerge [3]. Together with other advances made towards improving athletic performance, such as improved equipment and training methodology, researchers continued to study carbohydrate metabolism to better understand the mechanisms of how dietary carbohydrates improve performance, promote recovery and/or prevent fatigue, as well as researching strategies to optimize carbohydrate availability in athletes [7][8][9][10]. Over this period, understanding of the actions of dietary carbohydrates on exercise metabolism and performance has increased substantially and, in concert, nutritional recommendations for athletes have developed and continue to evolve to reflect contemporary knowledge and practice. ...
The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.
... However, the optimum diet and exercise regime remains elusive, and diet and exercise interventions often have highly variable outcomes between individuals. This is evident in sports science, where defined diet strategies have been designed to optimise energy availability and complement athletic outcomes [3]. Yet, individual factors are the main determinant of athletic performance. ...
Diet, exercise and the gut microbiome are all factors recognised to be significant contributors to cardiometabolic health. However, diet and exercise interventions to modify the gut microbiota to improve health are limited by poor understanding of the interactions between them. In this pilot study, we explored diet–exercise–microbiome dynamics in bodybuilders as they represent a distinctive group that typically employ well-defined dietary strategies and exercise regimes to alter their body composition. We performed longitudinal characterisation of diet, exercise, the faecal microbial community composition and serum metabolites in five bodybuilders during competition preparation and post-competition. All participants reduced fat mass while conserving lean mass during competition preparation, corresponding with dietary energy intake and exercise load, respectively. There was individual variability in food choices that aligned to individualised gut microbial community compositions throughout the study. However, there was a common shift from a high protein, low carbohydrate diet during pre-competition to a more macronutrient-balanced diet post-competition,
which was associated with similar changes in the gut microbial diversity across participants. The circulating metabolite profiles also reflected individuality, but a subset of metabolites relating to lipid
metabolism distinguished between pre- and post-competition. Changes in the gut microbiome and circulating metabolome were distinct for each individual, but showed common patterns. We conclude that further longitudinal studies will have greater potential than cross-sectional studies in informing personalisation of diet and exercise regimes to enhance exercise outcomes and improve health.
... Как правило, высокопрофессиональные спортсмены придерживаются специального рациона, особенно в тренировочный и предсоревновательный периоды. Нутритивный состав рационов варьирует в зависимости от вида и продолжительности тренировок для получения максимальной пользы от поступающих веществ и повышения эффективности тренировки, что лежит в основе производительности спортсменов [1][2][3]. ...
It is known that under conditions of ultra-high physical activity and a specific diet, the state of the microbiota plays a significant role in maintaining the health, metabolic and energy status of athletes. The purpose of the study was to evaluate the composition of blood microbial markers in professional football players and physically active people and their correlation with diets in order to substantiate recommendations for their optimization. Material and methods. In a cross-sectional study a group of football players (n=24, 28±3 years old, body mass index - 22.5±1.0 kg/m2) who received a diet according to the training regimen, and a comparison group of physically active individuals (n=25, 34±5 years old, body mass index - 21.8±2.8 kg/m2) have been examined. The method of gas chromatography-mass spectrometry was used to analyze microbial markers of microbiome, mycobiome, virome and blood metabolome populations. Data on actual dietary intake were collected using food diaries for 3 days, followed by data processing with the Nutrium 2.13.0 nutritional computer program. For analysis, individual daily requirements for energy and macronutrients have been calculated based on the basal metabolic rate (according to the Mifflin-San Geor formula, taking into account anthropometric data), the coefficient of physical activity (groups IV and II, respectively). Results. The analysis of the athletes' diet, compared with individual requirements and with the recommendations of the International Society for Sports Nutrition (ISSN), revealed a lack of complex carbohydrates (5±1 instead of 6.1±0.3 g/kg body weight day), an excess of sugars (23±4 instead of <10% of kcal). These figures are significantly higher than the intake of similar nutrients in physically active people in the comparison group. In football players, compared with the comparison group, significant changes in microbial markers were found for Alcaligenes spp., Clostridium ramosum, Coryneform CDC-group XX, Staphylococcus epidermidis (p<0.001), known for their pro-inflammatory activity in the intestine, as well as for Lactobacillus spp. (p<0.001) performing a protective function. In addition, mycobiome markers were increased in athletes: Candida spp. (p<0.001), Aspergillus spp. (p<0.001), among which there are potential pathogens of mycoses. This was not observed in the comparison group. At the same time, an increase in the microbial markers of Alcaligenes spp., Coryneform CDC-group XX, Lactobacillus spp., Streptomyces spp., Candida spp. Micromycetes spp., containing campesterol in the cell wall, in football players positively correlated with a high calorie diet (p<0.001). A similar correlation of mycobiome markers (Micromycetes spp., containing sitosterol in the cell wall, ρ=0.346, p=0.015) was observed with an excess of easily digestible carbohydrates. Taking into account the data obtained, a correction of the diet have been proposed: increasing the consumption of carbohydrates to 7.3-7.5 g/kg of body weight/day by including bakery products from whole grain flour and cereals in the diet (up to 300-370 g/day), limiting simple sugars (up to 90-95 g/day). Conclusion. High physical activity leads to changes in the structure of blood microbial markers, including a shift towards an increase in potentially pathogenic fungi. Wherein, a predictive role is played by an imbalance of macronutrients in terms of quantitative and qualitative composition, an excess of simple sugars, and a lack of slowly digestible carbohydrates. To correct the diet, an additional inclusion in the diet of their main sources - products from cereals (cereals and bakery products) is proposed.
... Though there was a small increase in carbohydrate intake with increasing EEE (Figure 3), the athletes consumed excess carbohydrate on 67% of "Rest" days and insufficient carbohydrate on 30% of "High" and 70% of "Very High" training volume days, relative to guideline recommendations (Thomas et al., 2016). Therefore, in the majority of the cases, our cohort failed to adequately match their carbohydrate intake to their training volume in accordance with contemporary nutrition guidelines (Burke, Hawley et al., 2018;Impey et al., 2018;Stellingwerff, 2018;Thomas et al., 2016). Collectively, these findings suggest that when elite endurance athletes are left to their own means in relation to their nutrition, they fail to ingest carbohydrates in line with current guidelines, resulting in lower energy (and carbohydrate) availability when undertaking a higher training volume. ...
The physiological effects of low energy availability (EA) have been studied using a homogenous daily EA pattern in laboratory settings. However, whether this daily EA pattern represents those of free-living athletes and is therefore ecologically valid is unknown. To investigate this, we assessed daily exercise energy expenditure, energy intake and EA in 10 free-living elite male road cyclists (20 min Mean Maximal Power: 5.27 ± 0.25 W · kg⁻¹) during 7 consecutive days of late pre-season training. Energy intake was measured using the remote-food photography method and exercise energy expenditure estimated from cycling crank-based power-metres. Seven-day mean ± SD energy intake and exercise energy expenditure was 57.9 ± 10.4 and 38.4 ± 8.6 kcal · kg FFM⁻¹ · day⁻¹, respectively. EA was 19.5 ± 9.1 kcal · kg FFM⁻¹ · day⁻¹. Within-participants correlation between daily energy intake and exercise energy expenditure was .62 (95% CI: .43 – .75; P < .001), and .60 (95% CI: .41 – .74; P < .001) between carbohydrate intake and exercise energy expenditure. However, energy intake only partially compensated for exercise energy expenditure, increasing 210 kcal · day⁻¹ per 1000 kcal · day⁻¹ increase in expenditure. EA patterns displayed marked day-to-day fluctuation (range: −22 to 76 kcal · kg FFM⁻¹ · day⁻¹). The validity of research using homogenous low EA patterns therefore requires further investigation.
... For example, the strategic periodization of dietary CHO in order to commence exercise with low muscle glycogen (during 3-10 weeks of training) enhances mitochondrial enzyme activity and protein content (Hansen et al. 2005;Morton et al. 2009;Yeo et al. 2008) and whole body and intra-muscular lipid metabolism (Hulston et al. 2010) and in some instances improves exercise capacity (Hansen et al. 2005) and performance (Marquet et al. 2016a, b), though performance enhancing effects are not always evident (Yeo et al. 2008;Hulston et al. 2010;Burke et al. 2017;Gejl et al. 2017a, b;. As such, the train-low paradigm and wider CHO periodization strategies have subsequently gained increased recognition among athletic populations (Stellingwerff 2012;Burke et al. 2018;Impey et al. 2018). It should also be noted that some of the enhanced adaptations associated with "train-low" (at least in the twice per day training model) may be due to performing two consecutive training sessions in close proximity to one another, as opposed to the effects of low pre-exercise muscle glycogen per se (Andrade-Souza et al. 2020). ...
Muscle glycogen is an important fuel source for contracting skeletal muscle, and it is well documented that exercise performance is impaired when the muscle’s stores of glycogen are exhausted. The role of carbohydrate (CHO) availability on exercise performance has been known for more than a century, while the specific role of muscle glycogen for muscle function has been known for half a century. Nonetheless, the precise cellular and molecular mechanisms by which glycogen availability regulates cell function and contractile-induced fatigue are unresolved. Alterations of pre-exercise muscle glycogen reserves by dietary and exercise manipulations or modifying the degree of dependency on endogenous glycogen during exercise have collectively established a close relationship between muscle glycogen and the resistance to fatigue. It is also apparent that glycogen availability regulates rates of muscle glycogenolysis and resynthesis, muscle glucose uptake, key steps in excitation-contraction coupling, and exercise-induced cell signaling regulating training adaptation. The present review provides both a historical and contemporary overview of the effects of exercise on muscle glycogen metabolism, addressing factors affecting glycogen use during exercise as well as the evolving concepts of how glycogen and glycolysis are integrated with cell function, skeletal muscle fatigue, and training adaptation.KeywordsGlycogenolysis, glycogen particleDietExerciseE-C coupling, fatigue, performance
... The ability to effectively oxidize fat for fuel, represented by a lower RER, is important for metabolic health [14] and long-duration exercise performance [15,16], and many athletes attempt to manipulate substrate oxidation during exercise as part of a periodized nutrition and training plan [17,18]. However, managing substrate oxidation during exercise is challenged by the influence of both modifiable The easily measured and easily modifiable factors related to exercise such as exercise duration and intensity, daily macronutrient intake, and pre-and peri-exercise carbohydrate intake, can only explain roughly one-third of the variation in RER during exercise. ...
Background:
Multiple factors influence substrate oxidation during exercise including exercise duration and intensity, sex, and dietary intake before and during exercise. However, the relative influence and interaction between these factors is unclear.
Objectives:
Our aim was to investigate factors influencing the respiratory exchange ratio (RER) during continuous exercise and formulate multivariable regression models to determine which factors best explain RER during exercise, as well as their relative influence.
Methods:
Data were extracted from 434 studies reporting RER during continuous cycling exercise. General linear mixed-effect models were used to determine relationships between RER and factors purported to influence RER (e.g., exercise duration and intensity, muscle glycogen, dietary intake, age, and sex), and to examine which factors influenced RER, with standardized coefficients used to assess their relative influence.
Results:
The RER decreases with exercise duration, dietary fat intake, age, VO2max, and percentage of type I muscle fibers, and increases with dietary carbohydrate intake, exercise intensity, male sex, and carbohydrate intake before and during exercise. The modelling could explain up to 59% of the variation in RER, and a model using exclusively easily modified factors (exercise duration and intensity, and dietary intake before and during exercise) could only explain 36% of the variation in RER. Variables with the largest effect on RER were sex, dietary intake, and exercise duration. Among the diet-related factors, daily fat and carbohydrate intake have a larger influence than carbohydrate ingestion during exercise.
Conclusion:
Variability in RER during exercise cannot be fully accounted for by models incorporating a range of participant, diet, exercise, and physiological characteristics. To better understand what influences substrate oxidation during exercise further research is required on older subjects and females, and on other factors that could explain additional variability in RER.
... The control diets varied in the composition of macronutrients. We classified the control diets based on the proportion of CHO intake as normal (NCHO) when CHO ≈40%-59%, high (HCHO) when CHO ≧60%, and periodized (PCHO), which includes training sessions and periods of some days in a fasted state (Burke et al. 2018). Table 1. ...
This systematic review with meta-analysis aimed to determine the effects of the ketogenic diet (KD) against carbohydrate (CHO)-rich diets on physical performance and body composition in trained individuals. The MEDLINE, EMBASE, CINAHL, SPORTDiscus, and The Cochrane Library were searched. Randomized and non-randomized controlled trials in athletes/trained adults were included. Meta-analytic models were carried out using Bayesian multilevel models. Eighteen studies were included providing estimates on cyclic exercise modes and strength one-maximum repetition (1-RM) performances and for total, fat, and free-fat masses. There were more favorable effects for CHO-rich than KD on time-trial performance (mode [95% credible interval]; −3.3% [−8.5%, 1.7%]), 1-RM (−5.7% [−14.9%, 2.6%]), and free-fat mass (−0.8 [−3.4, 1.9] kg); effects were more favorable to KD on total (−2.4 [−6.2, 1.8] kg) and fat mass losses (−2.4 [−5.4, 0.2] kg). Likely modifying effects on cyclic performance were the subject’s sex and VO2max, intervention and performance durations, and mode of exercise. The intervention duration and subjects’ sex were likely to modify effects on total body mass. KD can be a useful strategy for total and fat body losses, but a small negative effect on free-fat mass was observed. KD was not suitable for enhancing strength 1-RM or high-intensity cyclic performances.
... For the purposes of this review, the natural conclusion will be that since pre-exercise muscle glycogen content is determined by how much carbohydrate is ingested in the days prior to exercise (Figure 5), then a high-carbohydrate diet must always enhance performance in any exercise regardless of its duration or intensity. This is certainly the dietary advice that is now generally given [80][81][82][83][84][91][92][93][94]. ...
The introduction of the needle muscle biopsy technique in the 1960s allowed muscle tissue to be sampled from exercising humans for the first time. The finding that muscle glycogen content reached low levels at exhaustion suggested that the metabolic cause of fatigue during prolonged exercise had been discovered. A special pre-exercise diet that maximized pre-exercise muscle glycogen storage also increased time to fatigue during prolonged exercise. The logical conclusion was that the athlete’s pre-exercise muscle glycogen content is the single most important acutely modifiable determinant of endurance capacity. Muscle biochemists proposed that skeletal muscle has an obligatory dependence on high rates of muscle glycogen/carbohydrate oxidation, especially during high intensity or prolonged exercise. Without this obligatory carbohydrate oxidation from muscle glycogen, optimum muscle metabolism cannot be sustained; fatigue develops and exercise performance is impaired. As plausible as this explanation may appear, it has never been proven. Here, I propose an alternate explanation. All the original studies overlooked one crucial finding, specifically that not only were muscle glycogen concentrations low at exhaustion in all trials, but hypoglycemia was also always present. Here, I provide the historical and modern evidence showing that the blood glucose concentration—reflecting the liver glycogen rather than the muscle glycogen content—is the homeostatically-regulated (protected) variable that drives the metabolic response to prolonged exercise. If this is so, nutritional interventions that enhance exercise performance, especially during prolonged exercise, will be those that assist the body in its efforts to maintain the blood glucose concentration within the normal range.
... Limited availability of endogenous carbohydrate (CHO) stores prompts athletes to attempt dietary interventions aimed at maximizing oxidation of endogenous fat substrate, at exercise intensities relevant to prolonged endurance and ultra-endurance competition (Phinney et al., 1983;Volek et al., 2016;Burke et al., 2020). It has been shown that acute or chronic low-carbohydrate high-fat (LCHF) dietary interventions [e.g., ≤1 gCHO/kg body mass (BM)/ day] increase whole-body fat oxidation during prolonged aerobic exercise in both highly trained and recreationally competitive athletes compared to typical carbohydrate dietary provisions (e.g., ~6 gCHO/kgBM/day; Burke et al., 2018;Russo et al., 2021b). Maximum fat oxidation (MFO) rate of 1.54 vs. 0.67 g/min during an incremental graded exercise test, and MFO occurring at a greater percentage of VȮ 2max (Fat max ; 70.3 vs. 54.9%), ...
Using metadata from previously published research, this investigation sought to explore: (1) whole-body total carbohydrate and fat oxidation rates of endurance (e.g., half and full marathon) and ultra-endurance runners during an incremental exercise test to volitional exhaustion and steady-state exercise while consuming a mixed macronutrient diet and consuming carbohydrate during steady-state running and (2) feeding tolerance and glucose availability while consuming different carbohydrate regimes during steady-state running. Competitively trained male endurance and ultra-endurance runners ( n = 28) consuming a balanced macronutrient diet (57 ± 6% carbohydrate, 21 ± 16% protein, and 22 ± 9% fat) performed an incremental exercise test to exhaustion and one of three 3 h steady-state running protocols involving a carbohydrate feeding regime (76–90 g/h). Indirect calorimetry was used to determine maximum fat oxidation (MFO) in the incremental exercise and carbohydrate and fat oxidation rates during steady-state running. Gastrointestinal symptoms (GIS), breath hydrogen (H 2 ), and blood glucose responses were measured throughout the steady-state running protocols. Despite high variability between participants, high rates of MFO [mean (range): 0.66 (0.22–1.89) g/min], Fat max [63 (40–94) % V̇ O 2max ], and Fat min [94 (77–100) % V̇ O 2max ] were observed in the majority of participants in response to the incremental exercise test to volitional exhaustion. Whole-body total fat oxidation rate was 0.8 ± 0.3 g/min at the end of steady-state exercise, with 43% of participants presenting rates of ≥1.0 g/min, despite the state of hyperglycemia above resting homeostatic range [mean (95%CI): 6.9 (6.7–7.2) mmol/L]. In response to the carbohydrate feeding interventions of 90 g/h 2:1 glucose–fructose formulation, 38% of participants showed breath H 2 responses indicative of carbohydrate malabsorption. Greater gastrointestinal symptom severity and feeding intolerance was observed with higher carbohydrate intakes (90 vs. 76 g/h) during steady-state exercise and was greatest when high exercise intensity was performed (i.e., performance test). Endurance and ultra-endurance runners can attain relatively high rates of whole-body fat oxidation during exercise in a post-prandial state and with carbohydrate provisions during exercise, despite consuming a mixed macronutrient diet. Higher carbohydrate intake during exercise may lead to greater gastrointestinal symptom severity and feeding intolerance.
... Exercise prescription, for example, manipulating volume and intensity of physical training, is one such approach, which is demonstrated to attenuate the hormonal stress profile of BMT (Drain et al. 2017). Further, given the progress of sport nutrition (Burke et al. 2018), the recruits' nutrition during BMT offers an ongoing opportunity to support and enhance military physical training. Notwithstanding, these advances can be challenging to implement, in the military training environment, with suboptimal intakes of nutrients (Lutz et al. 2019). ...
This study described the whole blood fatty acid profile and Omega-3 Index (O3I) of Australian Army recruits at the commencement and completion of basic military training (BMT). Eighty males (17–34 y, 77.4 ± 13.0 kg, 43.5 ± 4.3 mL/kg/min) and 37 females (17–45 y, 64.3 ± 8.8 kg, 39.3 ± 2.7 mL/kg/min) volunteered to participate (N = 117). Whole blood samples of each recruit were collected using a finger prick in weeks 1 and 11 (n = 82) and analysed via gas chromatography for the relative proportions of each fatty acid (mean [95% confidence interval]). The macronutrient characteristics of the diet offerings was also determined. At commencement there was a low omega-3 status (sum of omega-3; 4.95% [4.82–5.07]) and O3I (5.03% [4.90–5.16]) and no recruit recorded an O3I >8% (desirable). The omega-6/omega-3 (7.04 [6.85–7.23]) and arachidonic acid/eicosapentaenoic acid (AA/EPA) (18.70 [17.86–19.53]) ratios for the cohort were also undesirable. The BMT mess menu provided a maximum of 190 mg/day of EPA and 260 mg/day of docosahexaenoic acid (DHA). The O3I of the recruits was lower by week 11 (4.62% [4.51–4.78], p < 0.05), the omega-6/omega-3 increased (7.27 [7.07–7.47], p < 0.05) and the AA/EPA remained elevated (17.85 [16.89–18.81]). In conclusion, Australian Army recruits’ omega-3 status remained undesirable during BMT and deserves nutritional attention.
Novelty: Australian Army recruits’ Omega-3 Index, at the commencement of BMT, was reflective of the Western-style diet. The BMT diet offered minimum opportunity for daily EPA and DHA consumption. Every recruit experienced a further reduction of their Omega-3 Index during BMT.
... The response to carbohydrate (CHO) ingestion and other aspects of substrate metabolism are also in large part genetically-determined. Carbohydrate plays a crucial role in high-intensity exercise performance, with athletes recommended to consume 60% of their energy from CHO. 59 Nevertheless, there are data to suggest a range of individual tolerances to CHO intake. Amylase is a digestive enzyme produced in the salivary glands and pancreas that breaks the molecular bonds of starch molecules into smaller saccharides (sugars) including small amounts of glucose. ...
Physical exertion was once crucial for survival because energy (food) was derived predominantly from hunting and foraging; this, in turn, shaped the genome of modern man. In contemporary society, human genes and human lives are incongruent; physical activity is no longer a prerequisite for securing calories, our jobs are largely sedentary, and scarcely is a predominance of leisure time devoted to structured exercise. Reducing sedentary time and following a structured exercise regimen has been shown, unequivocally, to improve long-term weight management and reduce the risk of noncommunicable diseases. Nevertheless, many are not meeting the most conservative of physical activity guidelines. This chapter begins by distinguishing among the terms of physical activity, exercise, and sport before overviewing the principal physiological benefits of regular exercise. There is a discussion of the juxtaposition between the benefits of regular exercise and the pathophysiological consequences of extreme exercise behavior. Finally, there is an overview of the genetically-inherited traits that mediate the physiological adaptation to exercise training and other molecular mechanisms that likely underpin exercise and performance.
... Deliberate restriction or reduction of EI and/or CHO availability may be involved when manipulation of body composition or training adaptation (e.g. low CHO availability training [116,117]) are desired outcomes of a training block. However, the phenomenon of an "inadvertent" mismatch between ad libitum EI and EEE is of most interest in situations of increased training loads/OTS. ...
The symptom similarities between training-overload (with or without an Overtraining Syndrome (OTS) diagnosis) and Relative Energy Deficiency in Sport (RED-S) are significant, with both initiating from a hypothalamic–pituitary origin, that can be influenced by low carbohydrate (CHO) and energy availability (EA). In this narrative review we wish to showcase that many of the negative outcomes of training-overload (with, or without an OTS diagnosis) may be primarily due to misdiagnosed under-fueling, or RED-S, via low EA and/or low CHO availability. Accordingly, we undertook an analysis of training-overload/OTS type studies that have also collected and analyzed for energy intake (EI), CHO, exercise energy expenditure (EEE) and/or EA. Eighteen of the 21 studies (86%) that met our criteria showed indications of an EA decrease or difference between two cohorts within a given study (n = 14 studies) or CHO availability decrease (n = 4 studies) during the training-overload/OTS period, resulting in both training-overload/OTS and RED-S symptom outcomes compared to control conditions. Furthermore, we demonstrate significantly similar symptom overlaps across much of the OTS (n = 57 studies) and RED-S/Female Athlete Triad (n = 88 studies) literature. It is important to note that the prevention of under-recovery is multi-factorial, but many aspects are based around EA and CHO availability. Herein we have demonstrated that OTS and RED-S have many shared pathways, symptoms, and diagnostic complexities. Substantial attention is required to increase the knowledge and awareness of RED-S, and to enhance the diagnostic accuracy of both OTS and RED-S, to allow clinicians to more accurately exclude LEA/RED-S from OTS diagnoses.
... Regardless of the precise mechanism, the present data indicate short-term CHO intakes of $2.4 g CHO·kg À1 ·day À1 ($21% EI) in recovery from exercise are sufficient to reduce muscle glycogen availability and alter substrate metabolism during subsequent moderate-intensity exercise, consistent with what might be expected from studies of non-ketogenic low-CHO, high-fat diets (33). Whether a "threshold" dietary CHO intake exists, somewhere between $2.5 and $4.5 g CHO·kg À1 ·day À1 (i.e., $20-45% EI), at which this metabolic shift takes place requires further investigation. ...
Altering dietary carbohydrate (CHO) intake modulates fuel utilization during exercise. However, there has been no systematic evaluation of metabolic responses to graded changes in short-term (< 1 week) dietary CHO intake. Thirteen active men performed interval running exercise combined with isocaloric diets over 3 days before evaluation of metabolic responses to 60-min running at 65% V̇O 2 max on three occasions. Diets contained lower (LOW, 2.40 ± 0.66 g CHO.kg ⁻¹ .d ⁻¹ , 21.3 ± 0.5% of energy intake [EI]), moderate (MOD, 4.98 ± 1.31 g CHO.kg ⁻¹ .d ⁻¹ , 46.3 ± 0.7% EI), or higher (HIGH, 6.48 ± 1.56 g CHO.kg ⁻¹ .d ⁻¹ , 60.5 ± 1.6% EI) CHO. Pre-exercise muscle glycogen content was lower in LOW (54.3 ± 26.4 mmol.kg ⁻¹ wet weight [ww]) compared to MOD (82.6 ± 18.8 mmol.kg ⁻¹ ww) and HIGH (80.4 ± 26.0 mmol.kg ⁻¹ ww, P<0.001; MOD vs. HIGH, P=0.85). Whole-body substrate oxidation, systemic responses, and muscle substrate utilization during exercise indicated increased fat and decreased CHO metabolism in LOW (RER: 0.81 ± 0.01) compared to MOD (RER 0.86 ± 0.01, P = 0.0005) and HIGH (RER: 0.88 ± 0.01, P < 0.0001; MOD vs. HIGH, P=0.14). Higher basal muscle expression of genes encoding proteins implicated in fat utilization was observed in LOW. In conclusion, muscle glycogen availability and subsequent metabolic responses to exercise were resistant to increases in dietary CHO intake from ~5.0 to ~6.5 g CHO.kg ⁻¹ .d ⁻¹ (46% to 61% EI), while muscle glycogen, gene expression and metabolic responses were sensitive to more marked reductions in CHO intake (~2.4 g CHO.kg ⁻¹ .d ⁻¹ , ~21% EI).
... Low-carbohydrate diets have been around for decades; however, this dietary practice remains poorly defined. Individuals adhering to a low-carbohydrate diet may vary from simply avoiding these food groups, reducing the amount of daily carbohydrate intake (< 100 g/day), to severely restricting the amount of daily carbohydrate intake (< 50 g/day) to induce ketosis [27,28]. Recommended macronutrient intake for female athletes range from 3 to 10 g/kg of the athlete's body weight per day for carbohydrates, 1.2-2.0 ...
Background
To determine if following specific diets was associated with reporting behaviors that are consistent with disordered eating compared to non-diet-adherent athletes. We hypothesized that athletes adhering to specific diets were more likely to report disordered eating than those not following a diet.
Methods
One thousand female athletes (15–30 years) completed a comprehensive survey about athletic health and wellness. Athletes were asked to specify their diet and completed 3 eating disorder screening tools: the Brief Eating Disorder in Athletes Questionnaire, the Eating Disorder Screen for Primary Care, and self-reported current or past history of eating disorder or disordered eating. Descriptive statistics were calculated for all study measures and chi-squared tests assessed relationships between athletes’ dietary practices and their responses to eating disorder screening tools. Statistical significance was defined as p < 0.05.
Results
Two hundred thirty-four of 1000 female athletes reported adherence to specific diets. 69 of the 234 diet-adhering athletes (29.5%) were excluded due to medically-indicated dietary practices or vague dietary descriptions. Of the 165 diet-adherent athletes, 113 (68.5%) screened positively to ≥1 of the 3 eating disorder screening tools. Specifically, athletes practicing a low-carbohydrate diet were more likely to report disordered eating vs. athletes without dietary restrictions (80% vs. 41.8%; p < 0.0001).
Conclusion
Specific diet adherence in female athletes may be associated with reporting behaviors that are consistent with disordered eating. Health practitioners should consider further questioning of athletes reporting specific diet adherence in order to enhance nutritional knowledge and help treat and prevent eating disorders or disordered eating.
... Exercise performed with reduced carbohydrate (CHO) availability can increase fat oxidation, increase the activation of cell signaling pathways, and promote oxidative adaptations in skeletal muscle [2,3]. At the same time, sufficient CHO ingestion before and/or during exercise is recommended for exercise sessions requiring a high quality, duration, and/or intensity [4]. It is therefore suggested that CHO ingestion be varied according to the goals and type of each exercise session to optimize both training adaptations and acute performance, yet there is wide variance among athletes regarding appropriate nutritional intake before exercise [5]. ...
Nutritional intake can influence exercise metabolism and performance, but there is a lack of research comparing protein-rich pre-exercise meals with endurance exercise performed both in the fasted state and following a carbohydrate-rich breakfast. The purpose of this study was to determine the effects of three pre-exercise nutrition strategies on metabolism and exercise capacity during cycling. On three occasions, seventeen trained male cyclists (VO2peak 62.2 ± 5.8 mL·kg−1·min−1, 31.2 ± 12.4 years, 74.8 ± 9.6 kg) performed twenty minutes of submaximal cycling (4 × 5 min stages at 60%, 80%, and 100% of ventilatory threshold (VT), and 20% of the difference between power at the VT and peak power), followed by 3 × 3 min intervals at 80% peak aerobic power and 3 × 3 min intervals at maximal effort, 30 min after consuming a carbohydrate-rich meal (CARB; 1 g/kg CHO), a protein-rich meal (PROTEIN; 0.45 g/kg protein + 0.24 g/kg fat), or water (FASTED), in a randomized and counter-balanced order. Fat oxidation was lower for CARB compared with FASTED at and below the VT, and compared with PROTEIN at 60% VT. There were no differences between trials for average power during high-intensity intervals (367 ± 51 W, p = 0.516). Oxidative stress (F2-Isoprostanes), perceived exertion, and hunger were not different between trials. Overall, exercising in the overnight- fasted state increased fat oxidation during submaximal exercise compared with exercise following a CHO-rich breakfast, and pre-exercise protein ingestion allowed similarly high levels of fat oxidation. There were no differences in perceived exertion, hunger, or performance, and we provide novel data showing no influence of pre-exercise nutrition ingestion on exercise-induced oxidative stress.
... Of note, specific characteristics of training and daily activities of the runner may be related to our observations. For instance, the runner followed an "Evolutionary periodization" [9], which accounts for management of both training loads and lifestyle habits, including professional activities, sleeping routines [15], nutritional strategies [16], and incidental physical activity [17] among others. In this regard, as the pre-planned loads were adapted on a daily basis, with consideration of all these factors (including HRV morning data [18]), we do not know if a fixed periodization would result in similar outcomes. ...
Background: The association between heart rate variability (HRV), training load (TL),
and performance is poorly understood. Methods: A middle-aged recreational female runner was monitored during a competitive 20-wk macrocycle divided into first (M1) and second mesocycle (M2) in which best performances over 10 km and 21 km were recorded. Volume (km), session rating of perceived exertion (sRPE), TL, and monotony (mean TL/SD TL) were the workload parameters recorded. The root mean square of the successive differences in R-R intervals (RMSSD), its coefficient of variation (RMSSDcv), and the RMSSD:RR ratio were the HRV parameters monitored. Results: During M2, RMSSD (p = 0.006) and RMSSD:RR (p = 0.002) were significantly increased, while RR was significantly reduced (p = 0.017). Significant correlations were identified between monotony and volume (r = 0.552; p = 0.012), RR (r = 0.447; p = 0.048), and RMSSD:RR (r = -0.458; p = 0.042). A sudden reduction in RMSSD (from 40.31 to 24.34 ms) was observed the day before the first symptoms of an influenza. Conclusions: The current results confirm the practicality of concurrent HRV and sRPE monitoring in recreational runners, with the RMSSD:RR ratio indicative of specific adaptations. Excessive training volume may be associated to both elevated monotony and reduced RMSSD:RR. Identification of mesocycle patterns is recommended for better individualization of the periodization used.
... Individuals adhering to a low-carbohydrate diet may vary from simply avoiding these food groups, reducing the amount of daily carbohydrate intake (< 100 g/day), to severely restricting the amount of daily carbohydrate intake (< 50 g/day) to induce ketosis. 23,24 In addition to medical indications or health and weight management bene ts, popular trends initiated by professional or high pro le athletes have also driven young athletes to participate in speci c diets despite the absence of scienti c evidence of performance bene ts. [3][4][5] Recent studies have shown that the majority of athletes practicing gluten-free diets have chosen to do so based on self-diagnosis, and despite lacking substantial evidence to support performance bene ts, there has been an increase in the prevalence of non-celiac, non-gluten sensitive athletes adopting a gluten-free diet in attempt to optimize health and enhance athletic performance. ...
BACKGROUND: To determine if following specific diets was associated with responding positively to eating disorder/disordered eating (ED/DE) screening tools compared to non-diet-adherent athletes. We hypothesized that athletes adhering to specific diets were more likely to respond positively on ED/DE screening tools than those not following a diet.
METHODS: 1000 female athletes (15-30 y) completed a comprehensive survey about athletic health and wellness. Athletes were asked to specify their diet and completed 3 ED/DE screening tools: the Brief Eating Disorder in Athletes Questionnaire, the Eating Disorder Screen for Primary Care, and self-reported current or past history of ED/DE. Descriptive statistics were calculated for all study measures and chi-squared tests assessed relationships between athletes’ dietary practices and their responses to ED/DE screening tools. Statistical significance was defined as p<0.05.
RESULTS: 234 of 1000 female athletes reported adherence to specific diets. 69 of the 234 diet-adhering athletes (29.5%) were excluded due to medically-indicated dietary practices or vague dietary descriptions. Of the 165 diet-adherent athletes, 122 (67.9%) responded positively to ≥1 of the 3 ED/DE screening tools. Athletes practicing vegetarian, vegan, low-carbohydrate, low-dairy, or ≥2 diets were more likely to respond positively to ≥1 ED/DE screening tool vs. athletes without dietary restrictions (70.0%, 77.8%, 79.5%, 60.0%, and 65.6%, respectively vs. 41.8%; p≤0.048).
CONCLUSION: Specific diet adherence in female athletes is associated with positive responses to ED/DE screening tools. Health practitioners should consider further ED/DE questioning of athletes reporting specific diet adherence in order to enhance nutritional knowledge and help treat and prevent ED/DE.
... Additionally, a number of investigations have assessed the impact of combining CHO with other presumably ergogenic substances to determine whether additive or synergistic benefits result (Jeukendrup et al. 1998;Saunders et al. 2004;Acker-Hewitt et al. 2012;Cox et al. 2016). As with novel supplements, these dietary and supplementation strategies have drawn substantial notoriety and have become hotly debated topics within popular and sport cultures (Burke et al. 2018). ...
Purpose
To critically examine the research on novel supplements and strategies designed to enhance carbohydrate delivery and/or availability.
Methods
Narrative review.
Results
Available data would suggest that there are varying levels of effectiveness based on the supplement/supplementation strategy in question and mechanism of action. Novel carbohydrate supplements including multiple transportable carbohydrate (MTC), modified carbohydrate (MC), and hydrogels (HGEL) have been generally effective at modifying gastric emptying and/or intestinal absorption. Moreover, these effects often correlate with altered fuel utilization patterns and/or glycogen storage. Nevertheless, performance effects differ widely based on supplement and study design. MTC consistently enhances performance, but the magnitude of the effect is yet to be fully elucidated. MC and HGEL seem unlikely to be beneficial when compared to supplementation strategies that align with current sport nutrition recommendations. Combining carbohydrate with other ergogenic substances may, in some cases, result in additive or synergistic effects on metabolism and/or performance; however, data are often lacking and results vary based on the quantity, timing, and inter-individual responses to different treatments. Altering dietary carbohydrate intake likely influences absorption, oxidation, and and/or storage of acutely ingested carbohydrate, but how this affects the ergogenicity of carbohydrate is still mostly unknown.
Conclusions
In conclusion, novel carbohydrate supplements and strategies alter carbohydrate delivery through various mechanisms. However, more research is needed to determine if/when interventions are ergogenic based on different contexts, populations, and applications.
... Most Olympic middle-and long-distance events are performed at intensities greater than 75% of VO 2max (2,3) and are therefore heavily reliant on CHO metabolism as maximal rates of lipid oxidation occur at~60%-65% VO 2max (4) and decline as exercise intensity increases. As a result, nutrition guidelines for endurance sport have focused heavily on matching the energy cost of the event to the body's finite storage CHO (5), while scientists and athletes have both searched for strategies that promote "glycogen sparing" for use later in exercise. Two strategies that have received recent attention are chronic adaptation to a ketogenic low-CHO, high-fat (LCHF) diet and acute supplementation with exogenous ketones (i.e., ketone esters [KE] or ketone salts). ...
Consumption of a ketogenic low-carbohydrate (CHO), high-fat (LCHF) diet increases skeletal muscle fat utilization but impairs exercise economy. Whether the concomitant increase in circulating endogenous ketone bodies (KB) alters the capacity to metabolize exogenous ketone supplements such as the popular ketone monoester (KE) is unknown.
Purpose: To determine if LCHF and KE supplementation can synergistically alter exercise metabolism and improve performance.
Methods: Elite race walkers (n=18, 15 male, 3 female; V[Combining Dot Above]O2peak 62 ± 6 mL·min·kg) undertook a 4-stage exercise economy test and real-life 10,000 m race prior to and following a 5-d isoenergetic high CHO (HCHO; ~60-65% CHO, 20% fat; n=9) or LCHF (75-80% fat, <50 g/day CHO, n=9) diet. The LCHF group performed additional economy tests pre/post diet after supplementation with 573 mg·kg body mass KE (HVMN, HVMN Inc.), which was also consumed for Race 2.
Results: The oxygen cost of exercise (relative V[Combining Dot Above]O2, mL·min·kg) increased across all 4 stages following LCHF (p<0.005). This occurred in association with increased fat oxidation rates, with a reciprocal decrease in CHO oxidation (p<0.001). Substrate utilisation in the HCHO group remained unaltered. Consumption of KE prior to the LCHF diet increased circulating KB (p<0.05), peaking at 3.2 ± 0.6 mM but did not alter V[Combining Dot Above]O2 or RER. LCHF diet elevated resting circulating KB (0.3 ± 0.1 vs. 0.1 ± 0.1 mM), but concentrations following supplementation did not differ from the earlier ketone trial. Critically, race performance was impaired by ~6% (p<0.0001) relative to baseline in the LCHF group but was unaltered in HCHO.
Conclusion: Despite elevating endogenous KB production, a LCHF diet does not augment the metabolic responses to KE supplementation, and negatively impacts race performance.
... Adequate exercise training is a robust strategy to increase strength, endurance and neuroplasticity (14,15). Furthermore, it is well established that diet composition can affect exercise capacity by altering the availability and utilization of the major energy source (16). Ingestion of carbohydrates prior to and during exercise can enhance endurance capacity. ...
Gamma-cyclodextrin (γCD) is a cyclic oligosaccharide consisting of eight α-(1,4)-linked glucopyranose subunits, which is often used in the food and pharmaceutical industries. However, little is known regarding the metabolic activity of "empty" γCD per se. Therefore, in the present study young C57BL/6 male mice received a control diet (CON) or an experimental diet that was supplemented with 12.88% γCD exchanged against corn starch. After 6 weeks of treatment, the voluntary wheel running activity was monitored and the muscle strength of mice was measured by employing Kondziela's inverted screen test and forelimb grip strength assay. The γCD-treated mice covered a significantly larger distance per night (CON 8.6 km, γCD 12.4 km) and were significantly longer active (CON 340 min, γCD 437 min). Moreover, γCD-treated mice significantly performed better at the inverted screen test indicated by an enhanced Kondziela score (CON 3.10, γCD 4.63). These data suggest that dietary γCD leads to an increased endurance. We also found a slightly anti-glycemic effect of γCD during oral glucose tolerance test. However, our mice from the γCD group exhibited no difference in terms of GLUT2 protein level in ileum tissue nor increased muscle glycogen storage. Furthermore, γCD exhibited no DPP-4 inhibitory activity in vitro. By analysing candidate muscle genes and proteins related to endurance and muscle performance we did not observe any differences in terms of Sirt1, Pgc1α, Cpt1b, Mef2c, Myh1 and Myh2 gene expression levels as well as total oxidative phosphorylation (OXPHOS), mtTFA and GLUT4 protein expression levels in skeletal muscle in response to γCD. We could not fully establish the exact underlying molecular mechanisms of the fitness improvement by dietary γCD which warrants further investigations.
... Exposure duration was an intervention period of at least 3 months to ensure that any body mass loss could be attributed to the dietary interventions and that it was not the result of short-term test-retest measurement error. Regarding the intervention condition, a threshold of 150 g/d of CHO was defined as a low CHO intake, based on the guidelines outlined by Burke et al. (19), whereas a ketogenic diet was defined as <50 g/d of CHO as agreed on by the Academy of Nutrition and Dietetics and the British Dietetic Association (20,21). Importantly, classification of intake was based on the actual CHO consumption achieved by participants and not the prescribed intake (i.e., this review is primarily concerned with the variability in body mass response when adhering to the specified diet and not the variability in adherence to the specified diet). ...
Objective:
An important notion in personalized medicine is that there is clinically relevant treatment response heterogeneity. Low-carbohydrate (CHO) and low-fat diets are widely adopted to reduce body mass. To compare individual differences in responses between two dietary interventions, a formal statistical comparison of response variances between study arms in a randomized controlled trial (RCT) is crucial.
Methods:
The change in variances in RCTs for the body mass responses to low-CHO dietary interventions versus change variances for the low-fat groups (typically considered as the comparator intervention) were compared. A literature search identified relevant RCTs (n = 25; 3,340 participants). The means and SDs of body mass change in low-CHO and low-fat study arms were extracted to calculate the variances of individual responses. These were meta-analyzed in a random-effects model and converted to the SD for individual responses.
Results:
The pooled SD for individual responses for body mass was 1.4 kg (95% CI: -1.1 to 2.3) with a wide 95% prediction interval of -6.3 to 10.4 kg.
Conclusions:
Evidence is insufficient to suggest the response heterogeneity to low-CHO diets differs from that observed with low-fat diets.
... As described in the previous section, lower training status and lack of training adaptation during the intervention may have contributed to the negative effects of the KD on performance. Time trial performance, which is generally more moderate in intensity, was no different (18,27,28,60) with a KD compared with CON, except for Burke et al. (37), which is described above. Overall, these data suggest moderate-to high-intensity exercise performance can be maintained, although training status should be considered when initiating a KD. ...
Use of high-fat, ketogenic diets (KDs) to support physical performance has grown in popularity over recent years. While these diets enhance fat and reduce carbohydrate oxidation during exercise, the impact of a KD on physical performance remains controversial. The objective of this work was to assess the effect of KDs on physical performance compared with mixed macronutrient diets [control (CON)]. A systematic review of the literature was conducted using PubMed and Cochrane Library databases. Randomized and nonrandomized studies were included if participants were healthy (free of chronic disease), nonobese [BMI (kg/m 2) <30], trained or untrained men or women consuming KD (<50 g carbohydrate/d or serum or whole-blood β-hydroxybutyrate >0.5 mmol/L) compared with CON (fat, 12-38% of total energy intake) diets for ≥14 d, followed by a physical performance test. Seventeen studies (10 parallel, 7 crossover) with 29 performance (13 endurance, 16 power or strength) outcomes were identified. Of the 13 endurance-type performance outcomes, 3 (1 time trial, 2 time-to-exhaustion) reported lower and 10 (4 time trials, 6 time-to-exhaustion) reported no difference in performance between the KD compared with CON. Of the 16 power or strength performance outcomes, 3 (1 power, 2 strength) reported lower, 11 (4 power, 7 strength) no difference, and 2 (power) enhanced performance in the KD compared with the CON. Risk of bias identified some concern of bias primarily due to studies allowing participants to self-select diet intervention groups and the inability to blind participants to the study intervention. Overall, the majority of null results across studies suggest that a KD does not have a positive or negative impact on physical performance compared with a CON diet. However, discordant results between studies may be due to multiple factors, such as the duration consuming study diets, training status, performance test, and sex differences, which will be discussed in this systematic review. Adv Nutr 2020;00:1-11.
... Lastly, athletes might benefit more from intermittent refeeds than overweight subjects as this population has reported favorable results following this protocol (159). This might be due to carbohydrate being pertinent for sports performance outcomes (160,161). Though not all kinds of sports may require high amounts of carbohydrate to improve performance (162,163), they are undoubtedly needed for high-intensity efforts (164,165). In a very recent study by Campbell et al. (166), resistance-trained subjects followed either a 21% CER or a 26% IER for 7 weeks. ...
As the scientific literature has continuously shown, weight loss attempts don`t always follow a linear fashion nor always go as expected even when the intervention is calculated with precise tools. One of the main reasons why this tends to happen relies on our body's biological drive to regain the weight we lose to survive. This phenomenon has been referred to as 'metabolic adaptation' many times in the literature and plays a very relevant role in the management of obesity and human body weight. This review will provide insight into some of the theoretical models for the etiology of metabolic adaptation as well as a quick look into the physiological and endocrine mechanisms that underlie it. Nutritional strategies and dietetic tools are thus necessary to confront these so-called adaptations to weight loss. Among some of these strategies we can highlight increasing protein needs, opting for high-fiber foods or programming controlled diet-refeeds, and diet-breaks over a large weight loss phase. Outside the nutritional aspects, it might be wise to increase the physical activity and thus the energy flux of an individual when possible to maintain diet-induced weight loss in the long-term. This review will examine these protocols and their viability in the context of adherence and sustainability for the individual towards successful weight loss.
ABSTRACT Dietary manipulation with high-protein or high-carbohydrate content are frequently employed during elite athletic training, aiming to enhance athletic performance. Such interventions are likely to impact upon gut microbial content. This study explored the impact of acute high-protein or high-carbohydrate diets on measured endurance performance and associated gut microbial community changes. In a cohort of well-matched, highly trained endurance runners, we measured performance outcomes, as well as gut bacterial, viral (FVP), and bacteriophage (IV) communities in a double-blind, repeated-measures design randomized control trial (RCT) to explore the impact of dietary intervention with either high-protein or high-carbohydrate content. High-dietary carbohydrate improved time-trial performance by +6.5% (P
Cycling is predominantly an endurance sport in which fuel utilization for energy production relies on the availability and delivery of oxygen to exercising muscle. Nutrition and training interventions to improve endurance performance are continually evolving, but ultimately, prescription should aim to generate improvements in cycling power and velocity while prioritizing athlete health and well-being. The wide range of cycling events and the different environments in which events take place pose a variety of nutrition-related challenges for cyclists. This review addresses some of these challenges and highlights recent advancements in nutrition for cycling performance.
New findings:
What is the topic of this review? The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them. What advances does it highlight? A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event-specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real-life sport for optimal implementation.
Abstract:
High-performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low-carbohydrate high-fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst-driven drinking) to fluid intake.
In the past decades, researchers have extensively studied (elite) athletes' physiological responses to understand how to maximize their endurance performance. In endurance sports, whole-body measurements such as the maximal oxygen consumption, lactate threshold, and efficiency/economy play a key role in performance. Although these determinants are known to interact, it has also been demonstrated that athletes rarely excel in all three. The leading question is how athletes reach exceptional values in one or all of these determinants to optimize their endurance performance, and how such performance can be explained by (combinations of) underlying physiological determinants. In this review, we advance on Joyner and Coyle's conceptual framework of endurance performance, by integrating a meta-analysis of the interrelationships, and corresponding effect sizes between endurance performance and its key physiological determinants at the macroscopic (whole-body) and the microscopic level (muscle tissue, i.e., muscle fiber oxidative capacity, oxygen supply, muscle fiber size, and fiber type). Moreover, we discuss how these physiological determinants can be improved by training and what potential physiological challenges endurance athletes may face when trying to maximize their performance. This review highlights that integrative assessment of skeletal muscle determinants points toward efficient type-I fibers with a high mitochondrial oxidative capacity and strongly encourages well-adjusted capillarization and myoglobin concentrations to accommodate the required oxygen flux during endurance performance, especially in large muscle fibers. Optimisation of endurance performance requires careful design of training interventions that fine tune modulation of exercise intensity, frequency and duration, and particularly periodisation with respect to the skeletal muscle determinants.
Optimal carbohydrate and protein intakes are vital for modulating training adaptation, recovery, and exercise performance. However, the research base underpinning contemporary sport nutrition guidelines has largely been conducted in male populations with a lack of consensus on whether the menstrual phase and associated changes in sex hormones allow broad application of these principles to female athletes. The present review will summarise our current understanding of carbohydrate and protein requirements in female athletes across the menstrual cycle and provide a critical analysis on how they compare to male athletes. On the basis of current evidence, we consider it premature to conclude that female athletes require sex specific guidelines in relation to CHO or protein requirements provided energy needs are met. However, there is a need for further research using sport-specific competition and training related exercise protocols that rigorously control for prior exercise, CHO/energy intake, contraceptive use and phase of menstrual cycle. Our overarching recommendation is to use current recommendations as a basis for adopting an individualised approach that takes into account athlete specific training and competition goals whilst also considering personal symptoms associated with the menstrual cycle.
Martínez-Gómez, MG and Roberts, BM. Metabolic adaptations to weight loss: A brief review. J Strength Cond Res XX(X): 000-000, 2021-As the scientific literature has continuously shown, body mass loss attempts do not always follow a linear fashion nor always go as expected even when the intervention is calculated with precise tools. One of the main reasons why this tends to happen relies on our body's biological drive to regain the body mass we lose to survive. This phenomenon has been referred to as "metabolic adaptation" many times in the literature and plays a very relevant role in the management of obesity and human weight loss. This review will provide insights into some of the theoretical models for the etiology of metabolic adaptation as well as a quick look into the physiological and endocrine mechanisms that underlie it. Nutritional strategies and dietetic tools are thus necessary to confront these so-called adaptations to body mass loss. Among some of these strategies, we can highlight increasing protein needs, opting for high-fiber foods or programming-controlled diet refeeds, and diet breaks over a large body mass loss phase. Outside the nutritional aspects, it might be wise to increase the physical activity and thus the energy flux of an individual when possible to maintain diet-induced body mass loss in the long term. This review will examine these protocols and their viability in the context of adherence and sustainability for the individual toward successful body mass loss.
Purpose:
Greater leisure-time physical activity (LTPA) associates with healthier lives, but knowledge regarding occupational physical activity (OPA) is more inconsistent. DNA methylation (DNAm) patterns capture age-related changes in different tissues. We aimed to assess how LTPA and OPA are associated with three DNAm based epigenetic age estimates, namely DNAm Age, PhenoAge and GrimAge.
Methods:
The participants were young adult (21-25-year-old, n = 285) and older (55-74-year-old, n = 235) twin pairs, including 16 pairs with documented long-term LTPA discordance. Genome-wide DNAm from blood samples was used to compute DNAm Age, PhenoAge and GrimAge Age acceleration (Acc), which describes the difference between chronological and epigenetic ages. Physical activity was assessed with sport, leisure-time and work indices based on the Baecke Questionnaire. Genetic and environmental variance components of epigenetic age Acc were estimated by quantitative genetic modelling.Epigenetic age Acc was highly heritable in young adult and older twin pairs (~60%). Sport index was associated with slower and OPA with faster DNAm GrimAge Acc after adjusting the model for sex. Genetic factors and non-shared environmental factors in common with sport index explained 1.5-2.7% and 1.9-3.5%, respectively, of the variation in GrimAge Acc. The corresponding proportions considering OPA were 0.4-1.8% and 0.7-1.8%, respectively. However, these proportions were minor (<0.5%) after adjusting the model for smoking status.
Conclusions:
LTPA associates with slower and OPA with faster epigenetic aging. However, adjusting the models for smoking status, which may reflect the accumulation of unhealthy lifestyle habits, attenuated the associations.
Background & aims
Low-carbohydrate diets (LCD) have gained substantial attention in recent years for their potential in health promotion and treatment of diseases, but they remain controversial in nutrition guidelines and exercise performance. Herein, through a literature review, we discuss the current evidence base by considering management of LCD and potential coupling of these dietary regiments with physical exercise.
Methods
We performed a comprehensive literature review with no date limits as a means of including seminal to current studies.
Results
Reduction of CHO intake decreases muscle glycogen, yielding greater fat oxidation and associated metabolic benefits. LCD may promote fat mass loss and regulation of biochemical parameters, such as lipid and glycemic biomarkers. The therapeutic potential of LCD towards noncommunicable diseases, particularly obesity and its comorbidities, is therefore reasonable as a dietary candidate in this context. Potential benefits to this approach are linked to enhancement of mitochondrial gene expression and mitochondrial biogenesis. As such, LCD may be a feasible tool in a ‘periodized nutrition’ for athletes and within clinical scenarios. Long-term observational follow-up studies have demonstrated increased mortality and cardiovascular implications of LCD. However, harmful associations may depend on the food source (e.g., animal-based vs. plant-based foods).
Conclusion
LCD may decrease body mass, waist circumference, and improve fat and carbohydrate metabolism. When combined with exercise, LCD seems to be an effective strategy in regulating metabolic factors of cardiovascular diseases. Conversely, LCD may be associated with higher mortality and metabolic dysregulations if it contains large amounts of animal-based foods, particularly saturated fat.
Athletes may choose to perform exercise in the overnight-fasted state for a variety of reasons related to convenience, gut comfort, or augmenting the training response, but it is unclear how many endurance athletes use this strategy. We investigated the prevalence and determinants of exercise performed in the overnight-fasted state among endurance athletes using an online survey and examined differences based on sex, competitive level, and habitual dietary pattern. The survey was completed by 1,950 endurance athletes (51.0% female, mean age 40.9 ± 11.1 years). The use of fasted training was reported by 62.9% of athletes, with significant effects of sex ( p < .001, Cramer’s V [φ c ] = 0.18, 90% CI [0.14, 0.22]), competitive level ( p < .001, φ c = 0.09, 90% CI [0.5, 0.13]), and habitual dietary pattern noted ( p < .001, φ c = 0.26, 90% CI [0.22, 0.29]). Males, nonprofessional athletes, and athletes following a low-carbohydrate, high-fat diet were most likely to perform fasted training. The most common reasons for doing so were related to utilizing fat as a fuel source (42.9%), gut comfort (35.5%), and time constraints/convenience (31.4%), whereas the most common reasons athletes avoided fasted training were that it does not help their training (47.0%), performance was worse during fasted training (34.7%), or greater hunger (34.6%). Overall, some athletes perform fasted training because they think it helps their training, whereas others avoid it because they think it is detrimental to their training goals, highlighting a need for future research. These findings offer insights into the beliefs and practices related to fasted-state endurance training.
Key points:
Brief (5-6 d) adaptation to LCHF in elite athletes increased exercise fat oxidation to rates previously observed with medium (3-4 wk) or chronic (>12 month) adherence to this diet, with metabolic changes being washed out in a similar timeframe Increased fat utilisation during exercise was associated with a 5-8% increase in oxygen cost at speeds related to Olympic Program races Acute restoration of endogenous CHO availability (24 h HCHO diet, pre-race CHO) only partially restored substrate utilisation during a race warm-up. Fat oxidation continued to be elevated above Baseline values although it was lower than achieved by 5-6 d keto-adaptation; CHO oxidation only reached 61% and 78% of values previously seen at exercise intensities related to race events. Acute restoration of CHO availability failed to overturn the impairment of high-intensity endurance performance previously associated with LCHF adaptation, potentially due to the blunted capacity for CHO oxidation.
Abstract:
We investigated substrate utilisation during exercise after brief (5-6 d) adaptation to a ketogenic low-carbohydrate (CHO), high-fat (LCHF) and similar washout period. Thirteen world-class male race walkers completed economy testing, 25-km training and a 10,000 m race (Baseline), with high CHO availability (HCHO), repeating this (Adaptation) after 5-6 d LCHF (n = 7; CHO: <50 g d-1 , protein: 2.2 g kg-1 d-1 ; 80% fat) or HCHO (n = 6; CHO: 9.7 g kg-1 d-1 ; protein: 2.2 g kg-1 d-1 ). Adaptation race was undertaken after 24-hr HCHO and pre-race CHO (2 g kg-1 ), identical to Baseline race. Substantial (>200%) increases in exercise fat oxidation occurred in LCHF Adaptation economy and 25-km tests, reaching mean rates of ∼1.43 g min-1 . However, relative VO2 (mL min-1 kg-1 ) was higher (p < 0.0001), by ∼ 8% and 5% at speeds related to 50-km and 20-km events. During Adaptation Race warm-up in LCHF, rates of fat and CHO oxidation at these speeds were decreased and increased respectively (p < 0.001) compared with the previous day, but were not restored to Baseline values. Performance changes differed between groups (p = 0.009), with all HCHO athletes improving in Adaptation Race [5.7 (5.6)%], while 6/7 LCHF athletes were slower [2.2 (3.4)%]. Substrate utilisation returned to Baseline values after 5-6 d of HCHO. In summary, robust changes in exercise substrate use occurred in 5-6 days of extreme changes in CHO intake. However, adaptation to LCHF plus acute restoration of endogenous CHO availability failed to restore high-intensity endurance performance, with CHO oxidation rates remaining blunted. This article is protected by copyright. All rights reserved.
Background:
Skeletal muscle glycogen is an important energy source for muscle contraction and a key regulator of metabolic responses to exercise. Manipulation of muscle glycogen is therefore a strategy to improve performance in competitions and potentially adaptation to training. However, assessing muscle glycogen in the field is impractical, and there are no normative values for glycogen concentration at rest and during exercise.
Objective:
The objective of this study was to meta-analyse the effects of fitness, acute dietary carbohydrate (CHO) availability and other factors on muscle glycogen concentration at rest and during exercise of different durations and intensities.
Data source and study selection:
PubMed was used to search for original articles in English published up until February 2018. Search terms included muscle glycogen and exercise, filtered for humans. The analysis incorporated 181 studies of continuous or intermittent cycling and running by healthy participants, with muscle glycogen at rest and during exercise determined by biochemical analysis of biopsies.
Data analysis:
Resting muscle glycogen was determined with a meta-regression mixed model that included fixed effects for fitness status [linear, as maximal oxygen uptake ([Formula: see text]O2max) in mL·kg-1·min-1] and CHO availability (three levels: high, ≥ 6 g·kg-1 of CHO per day for ≥ 3 days or ≥ 7 g·kg-1 CHO per day for ≥ 2 days; low, glycogen depletion and low-CHO diet; and normal, neither high nor low, or not specified in study). Muscle glycogen during exercise was determined with a meta-regression mixed model that included fixed effects for fitness status, resting glycogen [linear, in mmol·kg-1 of dry mass (DM)], exercise duration (five levels, with means of 5, 23, 53 and 116 min, and time to fatigue), and exercise intensity (linear, as percentage of [Formula: see text]O2max); intensity, fitness and resting glycogen were interacted with duration, and there were also fixed effects for exercise modes, CHO ingestion, sex and muscle type. Random effects in both models accounted for between-study variance and within-study repeated measurement. Inferences about differences and changes in glycogen were based on acceptable uncertainty in standardised magnitudes, with thresholds for small, moderate, large and very large of 25, 75, 150 and 250 mmol·kg-1 of DM, respectively.
Results:
The resting glycogen concentration in the vastus lateralis of males with normal CHO availability and [Formula: see text]O2max (mean ± standard deviation, 53 ± 8 mL·kg-1·min-1) was 462 ± 132 mmol·kg-1. High CHO availability was associated with a moderate increase in resting glycogen (102, ± 47 mmol·kg-1; mean ± 90% confidence limits), whereas low availability was associated with a very large decrease (- 253, ± 30 mmol·kg-1). An increase in [Formula: see text]O2max of 10 mL·kg-1·min-1 had small effects with low and normal CHO availability (29, ± 44 and 67, ± 15 mmol·kg-1, respectively) and a moderate effect with high CHO availability (80, ± 40 mmol·kg-1). There were small clear increases in females and the gastrocnemius muscle. Clear modifying effects on glycogen utilisation during exercise were as follows: a 30% [Formula: see text]O2max increase in intensity, small (41, ± 20 mmol·kg-1) at 5 min and moderate (87-134 mmol·kg-1) at all other timepoints; an increase in baseline glycogen of 200 mmol·kg-1, small at 5-23 min (28-59 mmol·kg-1), moderate at 116 min (104, ± 15 mmol·kg-1) and moderate at fatigue (143, ± 33 mmol·kg-1); an increase in [Formula: see text]O2max of 10 mL·kg-1·min-1, mainly clear trivial effects; exercise mode (intermittent vs. continuous) and CHO ingestion, clear trivial effects. Small decreases in utilisation were observed in females (vs. males: - 30, ± 29 mmol·kg-1), gastrocnemius muscle (vs. vastus lateralis: - 31, ± 46 mmol·kg-1) and running (vs. cycling: - 70, ± 32 mmol·kg-1).
Conclusion:
Dietary CHO availability and fitness are important factors for resting muscle glycogen. Exercise intensity and baseline muscle glycogen are important factors determining glycogen use during exercise, especially with longer exercise duration. The meta-analysed effects may be useful normative values for prescription of endurance exercise.
Since the introduction of the muscle biopsy technique in the late 1960s, our understanding of the regulation of muscle glycogen storage and metabolism has advanced considerably. Muscle glycogenolysis and rates of carbohydrate (CHO) oxidation are affected by factors such as exercise intensity, duration, training status and substrate availability. Such changes to the global exercise stimulus exert regulatory effects on key enzymes and transport proteins via both hormonal control and local allosteric regulation. Given the well-documented effects of high CHO availability on promoting exercise performance, elite endurance athletes are typically advised to ensure high CHO availability before, during and after high-intensity training sessions or competition. Nonetheless, in recognition that the glycogen granule is more than a simple fuel store, it is now also accepted that glycogen is a potent regulator of the molecular cell signaling pathways that regulate the oxidative phenotype. Accordingly, the concept of deliberately training with low CHO availability has now gained increased popularity amongst athletic circles. In this review, we present an overview of the regulatory control of CHO metabolism during exercise (with a specific emphasis on muscle glycogen utilization) in order to discuss the effects of both high and low CHO availability on modulating exercise performance and training adaptations, respectively.
Deliberately training with reduced carbohydrate (CHO) availability to enhance endurance-training-induced metabolic adaptations of skeletal muscle (i.e. the ‘train low, compete high’ paradigm) is a hot topic within sport nutrition. Train-low studies involve periodically training (e.g., 30–50% of training sessions) with reduced CHO availability, where train-low models include twice per day training, fasted training, post-exercise CHO restriction and ‘sleep low, train low’. When compared with high CHO availability, data suggest that augmented cell signalling (73% of 11 studies), gene expression (75% of 12 studies) and training-induced increases in oxidative enzyme activity/protein content (78% of 9 studies) associated with ‘train low’ are especially apparent when training sessions are commenced within a specific range of muscle glycogen concentrations. Nonetheless, such muscle adaptations do not always translate to improved exercise performance (e.g. 37 and 63% of 11 studies show improvements or no change, respectively). Herein, we present our rationale for the glycogen threshold hypothesis, a window of muscle glycogen concentrations that simultaneously permits completion of required training workloads and activation of the molecular machinery regulating training adaptations. We also present the ‘fuel for the work required’ paradigm (representative of an amalgamation of train-low models) whereby CHO availability is adjusted in accordance with the demands of the upcoming training session(s). In order to strategically implement train-low sessions, our challenge now is to quantify the glycogen cost of habitual training sessions (so as to inform the attainment of any potential threshold) and ensure absolute training intensity is not compromised, while also creating a metabolic milieu conducive to facilitating the endurance phenotype.
This case study documents the performance of an elite-level, exceptionally well fat-adapted endurance athlete, as he reintroduced carbohydrate ingestion during high-intensity training. He had followed a strict low-carbohydrate high-fat (LCHF) diet for 2 years during which he ate approximately 80 g of carbohydrate per day and trained and raced while ingesting only water. While following this diet, he earned numerous podium finishes in triathlons of various distances. However, he approached us to test whether carbohydrate supplementation during exercise would further increase his high-intensity performance without affecting his fat-adaptation. This 7-week n=1 investigation included a 4-week habitual LCHF diet phase (LCHF) during which he drank only water during training and performance trials, and a 3-week habitual diet plus carbohydrate ingestion phase (LCHF+CHO), during which he followed his usual LCHF diet but ingested 60 g/h carbohydrate during 8 high-intensity training sessions and performance trials. After each phase, rates of fat oxidation and 30 s sprint, 4 min sprint, 20 km time trial (TT), and 100 km TT performances were measured. Compared to LCHF, 20 km TT time improved by 2.8 % after LCHF+CHO, which would be a large difference in competition. There was no change in 30 s sprint power; a small improvement in 4 min sprint power (1.6 %); and a small reduction in 100 km TT time (1.1%). We conclude that carbohydrate ingestion during exercise was likely beneficial for this fat-adapted athlete during high-intensity endurance-type exercise (4-30 min) but likely did not benefit his short sprint or prolonged endurance performance.
Purpose:
The present study investigated the effects of periodic CHO restriction on endurance performance and metabolic markers in elite endurance athletes.
Methods:
Twenty-six male elite endurance athletes (VO2max: 65.0 ml O2[BULLET OPERATOR]kg[BULLET OPERATOR]min) completed 4 weeks of regular endurance training, while matched and randomized into two groups training with (Low) or without (High) carbohydrate (CHO) manipulation three days a week. The CHO manipulation days consisted of a 1-hr high intensity bike session in the morning, recovery for 7 hrs while consuming isocaloric diets containing either high CHO (414±2.4 g) or low CHO (79.5±1.0 g), and a 2-hr moderate bike session in the afternoon with or without CHO. VO2max, maximal fat oxidation and power output during a 30-min time trial (TT) were determined before and after the training period. The TT was undertaken after 90 mins of intermittent exercise with CHO provision before the training period and both CHO and placebo after the training period. Muscle biopsies were analyzed for glycogen, citrate synthase (CS) and β-hydroxyacyl-coenzyme A dehydrogenase (HAD) activity, carnitine palmitoyltransferase (CPT1b) and phosphorylated acetyl-CoA carboxylase (pACC).
Results:
The training effects were similar in both groups for all parameters. On average, VO2max and power output during the 30-min TT increased by 5 ± 1% (P<0.05) and TT performance was similar after CHO and placebo during the preload phase. Training promoted overall increases in glycogen content (18 ± 5%), CS activity (11 ± 5%) and pACC (38 ± 19%) (P<0.05) with no differences between groups. HAD activity and CPT1b protein content remained unchanged.
Conclusion:
Superimposing periodic CHO restriction to 4 weeks of regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.
Purpose: Ketone bodies are energy substrates produced by the liver during prolonged fasting or low-carbohydrate diet. The ingestion of a ketone ester (KE) rapidly increases blood ketone levels independent of nutritional status. KE has recently been shown to improve exercise performance, but whether it can also promote post-exercise muscle protein or glycogen synthesis is unknown.
Methods: Eight healthy trained males participated in a randomized double-blind placebo-controlled crossover study. In each session, subjects undertook a bout of intense one-leg glycogen-depleting exercise followed by a 5-h recovery period during which they ingested a protein/carbohydrate mixture. Additionally, subjects ingested a ketone ester (KE) or an isocaloric placebo (PL).
Results: KE intake did not affect muscle glycogen resynthesis, but more rapidly lowered post-exercise AMPK phosphorylation and resulted in higher mTORC1 activation, as evidenced by the higher phosphorylation of its main downstream targets S6K1 and 4E-BP1. As enhanced mTORC1 activation following KE suggests higher protein synthesis rates, we used myogenic C2C12 cells to further confirm that ketone bodies increase both leucine-mediated mTORC1 activation and protein synthesis in muscle cells.
Conclusion: Our results indicate that adding KE to a standard post-exercise recovery beverage enhances the post-exercise activation of mTORC1 but does not affect muscle glycogen resynthesis in young healthy volunteers. In vitro, we confirmed that ketone bodies potentiate the increase in mTORC1 activation and protein synthesis in leucine-stimulated myotubes. Whether, chronic oral KE intake during recovery from exercise can facilitate training-induced muscular adaptation and remodeling need to be further investigated.
It is becoming increasingly clear that adaptations, initiated by exercise, can be amplified or reduced by nutrition. Various methods have been discussed to optimize training adaptations and some of these methods have been subject to extensive study. To date, most methods have focused on skeletal muscle, but it is important to note that training effects also include adaptations in other tissues (e.g., brain, vasculature), improvements in the absorptive capacity of the intestine, increases in tolerance to dehydration, and other effects that have received less attention in the literature. The purpose of this review is to define the concept of periodized nutrition (also referred to as nutritional training) and summarize the wide variety of methods available to athletes. The reader is referred to several other recent review articles that have discussed aspects of periodized nutrition in much more detail with primarily a focus on adaptations in the muscle. The purpose of this review is not to discuss the literature in great detail but to clearly define the concept and to give a complete overview of the methods available, with an emphasis on adaptations that are not in the muscle. Whilst there is good evidence for some methods, other proposed methods are mere theories that remain to be tested. ‘Periodized nutrition’ refers to the strategic combined use of exercise training and nutrition, or nutrition only, with the overall aim to obtain adaptations that support exercise performance. The term nutritional training is sometimes used to describe the same methods and these terms can be used interchangeably. In this review, an overview is given of some of the most common methods of periodized nutrition including ‘training low’ and ‘training high’, and training with low- and high-carbohydrate availability, respectively. ‘Training low’ in particular has received considerable attention and several variations of ‘train low’ have been proposed. ‘Training-low’ studies have generally shown beneficial effects in terms of signaling and transcription, but to date, few studies have been able to show any effects on performance. In addition to ‘train low’ and ‘train high’, methods have been developed to ‘train the gut’, train hypohydrated (to reduce the negative effects of dehydration), and train with various supplements that may increase the training adaptations longer term. Which of these methods should be used depends on the specific goals of the individual and there is no method (or diet) that will address all needs of an individual in all situations. Therefore, appropriate practical application lies in the optimal combination of different nutritional training methods. Some of these methods have already found their way into training practices of athletes, even though evidence for their efficacy is sometimes scarce at best. Many pragmatic questions remain unanswered and another goal of this review is to identify some of the remaining questions that may have great practical relevance and should be the focus of future research.
The gastrointestinal (GI) tract plays a critical role in delivering carbohydrate and fluid during prolonged exercise and can therefore be a major determinant of performance. The incidence of GI problems in athletes participating in endurance events is high, indicating that GI function is not always optimal in those conditions. A substantial body of evidence suggests that the GI system is highly adaptable. Gastric emptying as well as stomach comfort can be “trained” and perceptions of fullness decreased; some studies have suggested that nutrient-specific increases in gastric emptying may occur. Evidence also shows that diet has an impact on the capacity of the intestine to absorb nutrients. Again, the adaptations that occur appear to be nutrient specific. For example, a high-carbohydrate diet will increase the density of sodium-dependent glucose-1 (SGLT1) transporters in the intestine as well as the activity of the transporter, allowing greater carbohydrate absorption and oxidation during exercise. It is also likely that, when such adaptations occur, the chances of developing GI distress are smaller. Future studies should include more human studies and focus on a number of areas, including the most effective methods to induce gut adaptations and the timeline of adaptations. To develop effective strategies, a better understanding of the exact mechanisms underlying these adaptations is important. It is clear that “nutritional training” can improve gastric emptying and absorption and likely reduce the chances and/or severity of GI problems, thereby improving endurance performance as well as providing a better experience for the athlete. The gut is an important organ for endurance athletes and should be trained for the conditions in which it will be required to function.
Background:
"Sleep-low" consists of a sequential periodization of carbohydrate (CHO) availability-low glycogen recovery after "train high" glycogen-depleting interval training, followed by an overnight-fast and light intensity training ("train low") the following day. This strategy leads to an upregulation of several exercise-responsive signaling proteins, but the chronic effect on performance has received less attention. We investigated the effects of short-term exposure to this strategy on endurance performance.
Methods:
Following training familiarization, 11 trained cyclists were divided into two groups for a one-week intervention-one group implemented three cycles of periodized CHO intake to achieve the sleep-low strategy over six training sessions (SL, CHO intake: 6 g·kg(-1)·day(-1)), whereas the control group consumed an even distribution of CHO over the day (CON). Tests were a 2 h submaximal ride and a 20 km time trial.
Results:
SL improved their performance (mean: +3.2%; p < 0.05) compared to CON. The improvement was associated with a change in pacing strategy with higher power output during the second part of the test. No change in substrate utilization was observed after the training period for either group.
Conclusion:
Implementing the "sleep-low" strategy for one week improved performance by the same magnitude previously seen in a three-week intervention, without any significant changes in selected markers of metabolism.
Optimising training and performance through nutrition strategies is central to supporting elite sportspeople, much of which has focussed on manipulating the relative intake of carbohydrate and fat and their contributions as fuels for energy provision. The ketone bodies, namely acetoacetate, acetone, and β-hydroxybutyrate (βHB), are produced in the liver during conditions of reduced carbohydrate availability and serve as an alternative fuel source for peripheral tissues including brain, heart and skeletal muscle. Ketone bodies are oxidised as a fuel source during exercise, are markedly elevated during the post-exercise recovery period, and the ability to utilise ketone bodies is higher in exercise-trained skeletal muscle. The metabolic actions of ketone bodies can alter fuel selection through attenuating glucose utilisation in peripheral tissues, anti-lipolytic effects on adipose tissue, and attenuation of proteolysis in skeletal muscle. Moreover, ketone bodies can act as signalling metabolites with βHB acting as an inhibitor of histone deacetylases, an important regulator of the adaptive response to exercise in skeletal muscle. Recent development of ketone esters facilitates acute ingestion of βHB that results in nutritional ketosis without necessitating restrictive dietary practices. Initial reports suggest this strategy alters the metabolic response to exercise and improves exercise performance, while other lines of evidence suggest roles in recovery from exercise. The present review focuses on the physiology of ketone bodies during and after exercise and in response to training, with specific interest in exploring the physiological basis for exogenous ketone supplementation and potential benefits for performance and recovery in athletes.
Since the pioneering studies conducted in the 1960s in which glycogen status was investigated utilizing the muscle biopsy technique, sports scientists have developed a sophisticated appreciation of the role of glycogen in cellular adaptation and exercise performance, as well as sites of storage of this important metabolic fuel. While sports nutrition guidelines have evolved during the past decade to incorporate sport-specific and periodized manipulation of carbohydrate (CHO) availability, athletes attempt to maximise muscle glycogen synthesis between important workouts or competitive events so that fuel stores closely match to the demands of the prescribed exercise. Therefore, it is important to understand the factors that enhance or impair this biphasic process. In the early post-exercise period (0-4 h), glycogen depletion provides a strong drive for its own resynthesis, with the provision of carbohydrate (CHO; ~ 1 g/kg body mass [BM]) optimizing this process. During the later phase of recovery (4-24 h), CHO intake should meet the anticipated fuel needs of the training/competition, with the type, form and pattern of intake being less important than total intake. Dietary strategies that can enhance glycogen synthesis from sub-optimal amounts of CHO or energy intake are of practical interest to many athletes; in this scenario, the co-ingestion of protein with CHO can assist glycogen storage. Future research should identify other factors that enhance the rate of synthesis of glycogen storage in a limited time-frame, improve glycogen storage from a limited CHO intake or increase muscle glycogen supercompensation.
Elite athletes and coaches are in a constant search for training methods and nutritional strategies to support training and recovery efforts that may ultimately maximize athletes' performance. Recently, there has been a re-emerging interest in the role of ketone bodies in exercise metabolism, with considerable media speculation about ketone body supplements being routinely used by professional cyclists. Ketone bodies can serve as an important energy substrate under certain conditions, such as starvation, and can modulate carbohydrate and lipid metabolism. Dietary strategies to increase endogenous ketone body availability (i.e., a ketogenic diet) require a diet high in lipids and low in carbohydrates for ~4 days to induce nutritional ketosis. However, a high fat, low carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrate, which forms a key fuel source for skeletal muscle during intense endurance-type exercise. Recently, ketone body supplements (ketone salts and esters) have emerged and may be used to rapidly increase ketone body availability, without the need to first adapt to a ketogenic diet. However, the extent to which ketone bodies regulate skeletal muscle bioenergetics and substrate metabolism during prolonged endurance-type exercise of varying intensity and duration remains unknown. Therefore, at present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes' performance under conditions where evidence-based nutritional strategies are applied appropriately.
Using an amalgamation of previously studied "train-low" paradigms, we tested the effects of reduced carbohydrate (CHO) but high leucine availability on cell-signaling responses associated with exercise-induced regulation of mitochondrial biogenesis and muscle protein synthesis (MPS). In a repeated-measures crossover design, 11 males completed an exhaustive cycling protocol with high CHO availability before, during, and after exercise (HIGH) or alternatively, low CHO but high protein (leucine enriched) availability (LOW + LEU). Muscle glycogen was different (P < 0.05) pre-exercise (HIGH: 583 ± 158, LOW + LEU: 271 ± 85 mmol kg(-1) dw) but decreased (P < 0.05) to comparable levels at exhaustion (≈100 mmol kg(-1) dw). Despite differences (P < 0.05) in exercise capacity (HIGH: 158 ± 29, LOW + LEU: 100 ± 17 min), exercise induced (P < 0.05) comparable AMPKα2 (3-4-fold) activity, PGC-1α (13-fold), p53 (2-fold), Tfam (1.5-fold), SIRT1 (1.5-fold), Atrogin 1 (2-fold), and MuRF1 (5-fold) gene expression at 3 h post-exercise. Exhaustive exercise suppressed p70S6K activity to comparable levels immediately post-exercise (≈20 fmol min(-1) mg(-1)). Despite elevated leucine availability post-exercise, p70S6K activity remained suppressed (P < 0.05) 3 h post-exercise in LOW + LEU (28 ± 14 fmol min(-1) mg(-1)), whereas muscle glycogen resynthesis (40 mmol kg(-1) dw h(-1)) was associated with elevated (P < 0.05) p70S6K activity in HIGH (53 ± 30 fmol min(-1) mg(-1)). We conclude: (1) CHO restriction before and during exercise induces "work-efficient" mitochondrial-related cell signaling but; (2) post-exercise CHO and energy restriction maintains p70S6K activity at basal levels despite feeding leucine-enriched protein. Our data support the practical concept of "fuelling for the work required" as a potential strategy for which to amalgamate train-low paradigms into periodized training programs.
It is the position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine that the performance of, and recovery from, sporting activities are enhanced by well-chosen nutrition strategies. These organizations provide guidelines for the appropriate type, amount, and timing of intake of food, fluids, and supplements to promote optimal health and performance across different scenarios of training and competitive sport. This position paper was prepared for members of the Academy of Nutrition and Dietetics, Dietitians of Canada (DC), and American College of Sports Medicine (ACSM), other professional associations, government agencies, industry, and the public. It outlines the Academy’s, DC’s and ACSM’s stance on nutrition factors that have been determined to influence athletic performance and emerging trends in the field of sports nutrition. Athletes should be referred to a registered dietitian/nutritionist for a personalized nutrition plan. In the United States and in Canada, the Certified Specialist in Sports Dietetics (CSSD) is a registered dietitian/nutritionist and a credentialed sports nutrition expert.
Key points:
Blood glucose is an important fuel for endurance exercise. It can be derived from ingested carbohydrate, stored liver glycogen and newly synthesized glucose (gluconeogenesis). We hypothesized that athletes habitually following a low carbohydrate high fat (LCHF) diet would have higher rates of gluconeogenesis during exercise compared to those who follow a mixed macronutrient diet. We used stable isotope tracers to study glucose production kinetics during a 2 h ride in cyclists habituated to either a LCHF or mixed macronutrient diet. The LCHF cyclists had lower rates of total glucose production and hepatic glycogenolysis but similar rates of gluconeogenesis compared to those on the mixed diet. The LCHF cyclists did not compensate for reduced dietary carbohydrate availability by increasing glucose synthesis during exercise but rather adapted by altering whole body substrate utilization.
Abstract:
Endogenous glucose production (EGP) occurs via hepatic glycogenolysis (GLY) and gluconeogenesis (GNG) and plays an important role in maintaining euglycaemia. Rates of GLY and GNG increase during exercise in athletes following a mixed macronutrient diet; however, these processes have not been investigated in athletes following a low carbohydrate high fat (LCHF) diet. Therefore, we studied seven well-trained male cyclists that were habituated to either a LCHF (7% carbohydrate, 72% fat, 21% protein) or a mixed diet (51% carbohydrate, 33% fat, 16% protein) for longer than 8 months. After an overnight fast, participants performed a 2 h laboratory ride at 72% of maximal oxygen consumption. Glucose kinetics were measured at rest and during the final 30 min of exercise by infusion of [6,6-(2) H2 ]-glucose and the ingestion of (2) H2 O tracers. Rates of EGP and GLY both at rest and during exercise were significantly lower in the LCHF group than the mixed diet group (Exercise EGP: LCHF, 6.0 ± 0.9 mg kg(-1) min(-1) , Mixed, 7.8 ± 1.1 mg kg(-1) min(-1) , P < 0.01; Exercise GLY: LCHF, 3.2 ± 0.7 mg kg(-1) min(-1) , Mixed, 5.3 ± 0.9 mg kg(-1) min(-1) , P < 0.01). Conversely, no difference was detected in rates of GNG between groups at rest or during exercise (Exercise: LCHF, 2.8 ± 0.4 mg kg(-1) min(-1) , Mixed, 2.5 ± 0.3 mg kg(-1) min(-1) , P = 0.15). We conclude that athletes on a LCHF diet do not compensate for reduced glucose availability via higher rates of glucose synthesis compared to athletes on a mixed diet. Instead, GNG remains relatively stable, whereas glucose oxidation and GLY are influenced by dietary factors.
Purpose:
We investigated the effect of a chronic dietary periodization strategy on endurance performance in trained athletes.
Methods:
21 triathletes (V[Combining Dot Above]O2max: 58.7 ± 5.7 mL·min·kg) were divided into 2 groups: a "sleep-low" (SL, n = 11) and a control group (CON, n = 10) consumed the same daily carbohydrate (CHO) intake (6 g·kg·d) but with different timing over the day to manipulate CHO availability before and after training sessions. The "sleep low" strategy consisted of a 3-week training/diet intervention comprising three blocks of diet/exercise manipulations: 1) "train-high" interval training sessions (HIT) in the evening with high-CHO availability; 2) overnight CHO restriction ("sleeping-low"), and 3) "train-low" sessions with low endogenous and exogenous CHO availability. The CON group followed the same training program but with high CHO availability throughout training sessions (no CHO restriction overnight, training sessions with exogenous CHO provision).
Results:
There was a significant improvement in delta efficiency during submaximal cycling for SL versus CON (CON: +1.4 ± 9.3 %, SL: +11 ± 15 %, P<0.05). SL also improved supra-maximal cycling to exhaustion at 150% of peak aerobic power (CON: +1.63 ± 12.4 %, SL: +12.5 ± 19.0 %; P = 0.06) and 10 km running performance (CON: -0.10 ± 2.03 %, SL: -2.9 ± 2.15 %; P < 0.05). Fat mass was decreased in SL (CON: -2.6 ± 7.4; SL: -8.5 ± 7.4 %PRE, P < 0.01), but not lean mass (CON: -0.22 ± 1.0; SL: -0.16 ± 1.7 %PRE).
Conclusion:
Short-term periodization of dietary CHO availability around selected training sessions promoted significant improvements in submaximal cycling economy, as well as supra-maximal cycling capacity and 10 km running time in trained endurance athletes.
Background:
Many successful ultra-endurance athletes have switched from a high-carbohydrate to a low-carbohydrate diet, but they have not previously been studied to determine the extent of metabolic adaptations.
Methods:
Twenty elite ultra-marathoners and ironman distance triathletes performed a maximal graded exercise test and a 180 min submaximal run at 64% VO2max on a treadmill to determine metabolic responses. One group habitually consumed a traditional high-carbohydrate (HC: n=10, %carbohydrate:protein:fat=59:14:25) diet, and the other a low-carbohydrate (LC; n=10, 10:19:70) diet for an average of 20 months (range 9 to 36 months).
Results:
Peak fat oxidation was 2.3-fold higher in the LC group (1.54±0.18 vs 0.67±0.14 g/min; P=0.000) and it occurred at a higher percentage of VO2max (70