Article

# Low Carbohydrate, High Fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers

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## Abstract

Key points Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support. Adaptation to a ketogenic low carbohydrate, high fat (LCHF) diet markedly increases rates of whole‐body fat oxidation during exercise in race walkers over a range of exercise intensities. The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real‐life race performance in elite race walkers. In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity. Abstract We investigated the effects of adaptation to a ketogenic low carbohydrate (CHO), high fat diet (LCHF) during 3 weeks of intensified training on metabolism and performance of world‐class endurance athletes. We controlled three isoenergetic diets in elite race walkers: high CHO availability (g kg⁻¹ day⁻¹: 8.6 CHO, 2.1 protein, 1.2 fat) consumed before, during and after training (HCHO, n = 9); identical macronutrient intake, periodised within or between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (< 50 g day⁻¹ CHO; 78% energy as fat; 2.1 g kg⁻¹ day⁻¹ protein; LCHF, n = 10). Post‐intervention, V˙O2 peak during race walking increased in all groups (P < 0.001, 90% CI: 2.55, 5.20%). LCHF was associated with markedly increased rates of whole‐body fat oxidation, attaining peak rates of 1.57 ± 0.32 g min⁻¹ during 2 h of walking at ∼80% V˙O2 peak . However, LCHF also increased the oxygen (O2) cost of race walking at velocities relevant to real‐life race performance: O2 uptake (expressed as a percentage of new V˙O2 peak ) at a speed approximating 20 km race pace was reduced in HCHO and PCHO (90% CI: −7.047, −2.55 and −5.18, −0.86, respectively), but was maintained at pre‐intervention levels in LCHF. HCHO and PCHO groups improved times for 10 km race walk: 6.6% (90% CI: 4.1, 9.1%) and 5.3% (3.4, 7.2%), with no improvement (−1.6% (−8.5, 5.3%)) for the LCHF group. In contrast to training with diets providing chronic or periodised high‐CHO availability, and despite a significant improvement in V˙O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.

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... The concept of positive effects of keto-adaptation on endurance performance is still strongly challenged. Burke et al. [21] investigated the effect of a high-fat diet during a 3-week intensified training. In this study, increased rate of fat oxidation resulted in increased oxygen demand for a given work load, impairing exercise economy [21]. ...
... Burke et al. [21] investigated the effect of a high-fat diet during a 3-week intensified training. In this study, increased rate of fat oxidation resulted in increased oxygen demand for a given work load, impairing exercise economy [21]. Still today, exercise and sport nutrition guidelines recommend that endurance athletes eat more CHOs (7-10 g kg −1 d −1 ) than routine CHOs intake (5-7 g kg −1 d −1 ) to optimise muscle glycogen stores [22][23][24]. ...
... Increasing fat rate oxidation requires greater oxygen consumption, thus leading to higher maximal oxygen supply for maintaining a given exercise load [2]. Some evidence suggests a positive effect of a KD on VO 2 max [21,[28][29][30][31] but is contrasted by recent work of Burke et al. [21]. At present, these mixed findings are believed to be due to heterogeneity across studies and/or variability among athletes [32]. ...
Article
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Background A ketogenic diet (KD) reduces daily carbohydrates (CHOs) ingestion by replacing most calories with fat. KD is of increasing interest among athletes because it may increase their maximal oxygen uptake (VO2max), the principal performance limitation at high-altitudes (1500–3500 m). We examined the tolerance of a 4-week isocaloric KD (ICKD) under simulated hypoxia and the possibility of evaluating ICKD performance benefits with a maximal graded exercise bike test under hypoxia and collected data on the effect of the diet on performance markers and arterial blood gases. Methods In a randomised single-blind cross-over model, 6 recreational mountaineers (age 24–44 years) completed a 4-week ICKD followed or preceded by a 4-week usual mixed Western-style diet (UD). Performance parameters (VO2max, lactate threshold [LT], peak power [Ppeak]) and arterial blood gases (PaO2, PaCO2, pH, HCO3⁻) were measured at baseline under two conditions (normoxia and hypoxia) as well as after a 4-week UD and 4-week ICKD under the hypoxic condition. Results We analysed data for all 6 participants (BMI 19.9–24.6 kg m⁻²). Mean VO2max in the normoxic condition was 44.6 ml kg⁻¹ min⁻¹. Hypoxia led to decreased performance in all participants. With the ICKD diet, median values for PaO2 decreased by − 14.5% and VO2max by + 7.3% and Ppeak by + 4.7%. Conclusion All participants except one could complete the ICKD. VO2max improved with the ICKD under the hypoxia condition. Therefore, an ICKD is an interesting alternative to CHOs dependency for endurance performance at high-altitudes, including high-altitude training and high-altitude races. Nevertheless, decreased PaO2 with ICKD remains a significant limitation in very-high to extreme altitudes (> 3500 m). Trial registration Clinical trial registration Nr. NCT05603689 (Clinicaltrials.gov). Ethics approval CER-VD, trial Nr. 2020-00427, registered 18.08.2020—prospectively registered.
... From 1896 to 2008, athletes competing in the Olympics demonstrated trends for increased carbohydrate intake in 1976 and a predominant shift toward high-carbohydrate low-fat (HCLF) diets in the 1996 Olympic games (1)(2)(3). This shift in athlete food preference toward carbohydrates was cited to be driven by (i) increased user consciousness of healthy food choice to optimized performance (1,4,5); (ii) the importance of muscle glycogen as the preferable metabolic fuel during exercise of either high intensity or long duration low intensity (6)(7)(8)(9)(10)(11)(12) following the emergence of muscle biopsy techniques in 1960s (13); (iii) anaplerotic theory in which depleted muscle glycogen attenuates mitochondrial oxaloacetate concentrations and thus reduced mitochondrial capacity to oxidize fatty acids (14); (iv) multiple studies illustrating carbohydrate ingestion delayed or reversed fatigue by maintaining blood glucose homeostasis (15)(16)(17); (v) "cross-over effect" (18)(19)(20) in which exercise of increasing intensity becomes increasingly dependent on carbohydrate oxidation since fat oxidation effectively ceases at any exercise intensity ≥ 85% VO 2max (18)(19)(20)(21)(22); (vi) clinical trials of high-fat diets resulting in impaired performance in both recreational (23) and elite athletes (i.e., Olympic class) (24)(25)(26). ...
... Five key factors may have contributed to these differences: randomization, dietary controls during exercise, training load, body composition, and dietary habituation timeline. Prior studies with differing results allowed subjects to choose the diet they preferred (16)(17)(18). In addition, during the final performance trial involving simulated races of up to 25-km, subjects on the LCHF diet were provided with carbohydrate-free "non-caloric fluid (water or artificially sweetened drinks)" (16) and "LCHF cookies" (17) whereas subjects on the HCLF diet received "sports drink, sports gels and confectionary" providing "∼60g CHO" every hour (16,17). ...
... Prior studies with differing results allowed subjects to choose the diet they preferred (16)(17)(18). In addition, during the final performance trial involving simulated races of up to 25-km, subjects on the LCHF diet were provided with carbohydrate-free "non-caloric fluid (water or artificially sweetened drinks)" (16) and "LCHF cookies" (17) whereas subjects on the HCLF diet received "sports drink, sports gels and confectionary" providing "∼60g CHO" every hour (16,17). As a result, blood glucose levels were lower in the LCHF group in the two trials (16,17) in which it was measured, with a trend toward a progressive hypoglycemia in one trial [ figure 5A from (17)]. ...
Article
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High carbohydrate, low fat (HCLF) diets have been the predominant nutrition strategy for athletic performance, but recent evidence following multi-week habituation has challenged the superiority of HCLF over low carbohydrate, high fat (LCHF) diets, along with growing interest in the potential health and disease implications of dietary choice. Highly trained competitive middle-aged athletes underwent two 31-day isocaloric diets (HCLF or LCHF) in a randomized, counterbalanced, and crossover design while controlling calories and training load. Performance, body composition, substrate oxidation, cardiometabolic, and 31-day minute-by-minute glucose (CGM) biomarkers were assessed. We demonstrated: (i) equivalent high-intensity performance (@∼85%VO2max), fasting insulin, hsCRP, and HbA1c without significant body composition changes across groups; (ii) record high peak fat oxidation rates (LCHF:1.58 ± 0.33g/min @ 86.40 ± 6.24%VO2max; 30% subjects > 1.85 g/min); (iii) higher total, LDL, and HDL cholesterol on LCHF; (iv) reduced glucose mean/median and variability on LCHF. We also found that the 31-day mean glucose on HCLF predicted 31-day glucose reductions on LCHF, and the 31-day glucose reduction on LCHF predicted LCHF peak fat oxidation rates. Interestingly, 30% of athletes had 31-day mean, median and fasting glucose > 100 mg/dL on HCLF (range: 111.68-115.19 mg/dL; consistent with pre-diabetes), also had the largest glycemic and fat oxidation response to carbohydrate restriction. These results: (i) challenge whether higher carbohydrate intake is superior for athletic performance, even during shorter-duration, higher-intensity exercise; (ii) demonstrate that lower carbohydrate intake may be a therapeutic strategy to independently improve glycemic control, particularly in those at risk for diabetes; (iii) demonstrate a unique relationship between continuous glycemic parameters and systemic metabolism.
... However, even with as little as five days of implementing LCDs, increased fat oxidation (FATox) rates have been reported (14)(15)(16). While this increase in FATox is a consistent finding among most studies investigating the effect of LCDs in EA (6,(17)(18)(19)(20)(21)(22)(23)(24), the results regarding exercise performance are less clear. ...
... Additionally, Burke et al. (16,19,20) have elucidated a potential mechanism for performance impairment following a KD at higher intensities; specifically, they showed that exercise economy is reduced following a KD compared to HC and periodized CHO diets. ...
... To avoid any inferential interpretation of our TTC data, we will discuss our results in directional terms only. Our data suggests similar trends to the studies of Burke et al. (19,20) whether SFP was available as an analysis option in the MuscleSound ® cloud application at the time of that study. While we did not measure muscle glycogen content directly, and thus cannot speak to the relationship between SFP and muscle glycogen directly, we believe that SFP is a measure that is sensitive enough to detect changes induced by exercise and diet. ...
... This study examined the chronic and postprandial metabolic responses to a KD compared to a HCD and HD in a group of trained competitive cyclists and triathletes. While several studies have reported metabolic responses to a KD in endurance athletes, most studies have focused on exercise specific responses in comparison to a HCD [7,[32][33][34][35][36][37]. Our study is unique in its practical approach, where we examined the metabolic responses to an ad libitum KD in comparison to both an ad libitum HCD and the athlete's HD, which allowed us to compare both the KD and HCD to the athletes current dietary practices and show the effects more likely to be observed outside of a research setting. ...
... Few studies have examined the effects of a chronic KD on fasting EE in trained endurance athletes [7,[32][33][34][35][36][37]. Interestingly, insights toward our findings may be gleaned from studies investigating metabolic responses to a KD in individuals with overweight or obesity. ...
... Assuming that the HD test meal resembles the typical diet composition for this group of athletes and considering that fasting FatOx between the KD and HD were similar, one could question if there are distinguishable metabolic advantages of a KD compared to the typical Western diet followed by most recreational competitive cyclists and triathletes. Studies have shown that severe carbohydrate restriction impairs exercise economy and other performance measures in endurance athletes [36]. Thus, if an athlete's HD exhibits fasting and postprandial FatOx similar to a KD but without the caveat of restricting carbohydrates, what is the metabolic advantage of a KD over the athlete's habitual intake? ...
Article
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Extreme carbohydrate deficits during a ketogenic diet (KD) may result in metabolic adaptations reflective of low energy availability; however, the manifestation of these adaptations outside of exercise have yet to be elucidated in cyclists and triathletes. The purpose of this study is to investigate the chronic and postprandial metabolic responses to a KD compared to a high-carbohydrate diet (HCD) and habitual diet (HD) in trained competitive cyclists and triathletes. For this randomized crossover trial, six trained competitive cyclist and triathletes (F: 4, M: 2) followed an ad libitum KD and HCD for 14 d each after their HD. Fasting energy expenditure (EE), respiratory exchange ratio (RER), and fat and carbohydrate oxidation (FatOx and CarbOx, respectively) were collected during their HD and after 14 d on each randomly assigned KD and HCD. Postprandial measurements were collected on day 14 of each diet following the ingestion of a corresponding test meal. There were no significant differences in fasting EE, RER, FatOx, or CarbOx among diet conditions (all p > 0.050). Although postprandial RER and CarbOx were consistently lower following the KD meal, there were no differences in peak postprandial RER (p = 0.452), RER incremental area under the curve (iAUC; p = 0.416) postprandial FatOx (p = 0.122), peak FatOx (p = 0.381), or FatOx iAUC (p = 0.164) between the KD and HD meals. An ad libitum KD does not significantly alter chronic EE or substrate utilization compared to a HCD or HD; postprandial FatOx appears similar between a KD and HD; this is potentially due to the high metabolic flexibility of cyclists and triathletes and the metabolic adaptations made to habitual high-fat Western diets in practice. Cyclists and triathletes should consider these metabolic similarities prior to a KD given the potential health and performance impairments from severe carbohydrate restriction.
... 24 in a series of studies among elite race walkers, adaptation to a lchf diet increased fat oxidation but resulted in an increased oc, i.e. reduced economy, to walk at the speeds relevant to real life competitive events. [25][26][27][28] finally, in a study among swimmers, no difference in swimming economy was observed between swimmers who consumed a lchf diet or a high carbohydrate, low fat (hclf) diet. 29 despite these studies, knowledge of the effect of dietary macronutrient composition on exercise efficiency and economy is limited. ...
... These differences were only statistically significant after 2 days on the diet, although there was a strong tendency for oc to remain higher after 14 days on the diet. These results replicate earlier observations [23][24][25][26][27][28] and resemble physiological differences expected after adaptation to a lchf diet. ...
... exercise economy can be characterized in different ways, e.g. as Vo 2 (ml/min) or as %Vo 2max for a given workload or speed using a step-wise protocol. [24][25][26][27][28] We chose to use the term oc and to express it anchored to the changing workload in our study (ml o 2 / kcal), as the intended 60% W max exercise intensity had to be reduced on several occasions. not correcting for these changes in workload would have flawed our observations. ...
Article
Background: Exercise efficiency and economy are key determinants of endurance exercise performance. In this cross-over intervention trial, we investigated the effect of adherence to a low carbohydrate, high fat (LCHF) diet versus a high carbohydrate (HC) diet on gross efficiency (GE) and oxygen cost (OC) during exercise, both after 2 days and after 14 days of adherence. Methods: Fourteen recreational male athletes followed a two week LCHF diet (<10 energy % carbohydrate) and a two week HC diet (>50 energy % carbohydrate), in random order, with a wash-out period of three weeks in between. After 2 and 14 days on each diet, the athletes performed a 90 minutes submaximal exercise session on a bicycle ergometer. Indirect calorimetry measurements were done after 60 minutes of exercise to calculate GE and OC. Results: GE was significantly lower on the LCHF diet compared to the HC diet, after 2 days (17.6 ± 1.9 vs 18.8 ± 1.2 %, p=0.011, for the LCHF and HC diet respectively), not after 14 days. OC was significantly higher on the LCHF diet compared to the HC diet, after 2 days (1191 ± 138 vs 1087 ± 72 ml O2/kCal, p=0.003, for the LCHF and HC diet respectively), and showed a strong tendency to remain higher after 14 days, p=0.018. Conclusions: Although LCHF diets are popular strategies to increase fat oxidation during exercise, adherence to a LCHF diet was associated with a lower exercise efficiency and economy compared to a HC diet.
... However, several studies suggested that fat is an inferior metabolic fuel that cannot support higher-intensity exercise [28][29][30]; therefore, the fat-dominated strategy from LCHF may not be optimal. This is also supported by the findings from several studies [31][32][33]. For example, Zinn et al. observed a decrease in aerobic performance and no improvement in lean body mass in trained participants following a 10-week training of CT combined with LCHF [33]. ...
... Next, these 30 full-text articles were evaluated for eligibility, and 22 of them were excluded. Finally, after completing the thorough full-text review, eight publications (Table 1) consisting of 170 participants were included in the quantitative synthesis [26,31,32,[46][47][48][49][50]. No disagreement was met between the two authors and all the papers included complete data that were needed for the review and meta-analysis. ...
... The sample size of the included studies ranged from 16 to 27 participants, with participants ranging in age from 23 to 35.4 years. Four studies [26,32,46,50] consisted of men only and the other four studies [31,[47][48][49] included both men and women. Participants included in the studies were all physically active participants, including recreationally trained participants, as defined by training in a gym or club in spare time [47][48][49][50] and professionally trained participants, as defined by training in professional or national training institutions and participating in competitions [31,32,51,52]. ...
Article
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(1) Background: Recently, studies have emerged to explore the effects of concurrent training (CT) with a low-carb, high-fat ketogenic diet (LCHF) on body composition and aerobic performance and observed its benefits. However, a large variance in the study design and observations is presented, which needs to be comprehensively assessed. We here thus completed a systematic review and meta-analysis to characterize the effects of the intervention combining CT and LCHF on body composition and aerobic capacity in people with training experience as compared to that combining CT and other dietary strategies. (2) Methods: A search strategy based on the PICOS principle was used to find literature in the databases of PubMed, Web of Science, EBSCO, Sport-discuss, and Medline. The quality and risk of bias in the studies were independently assessed by two researchers. (3) Result: Eight studies consisting of 170 participants were included in this work. The pooled results showed no significant effects of CT with LCHF on lean mass (SMD = −0.08, 95% CI −0.44 to 0.3, p = 0.69), body fat percentage (SMD = −0.29, 95% CI −0.66 to 0.08, p = 0.13), body mass (SMD = −0.21, 95% CI −0.53 to 0.11, p = 0.2), VO2max (SMD = −0.01, 95% CI −0.4 to 0.37, p = 0.95), and time (or distance) to complete the aerobic tests (SMD = −0.02, 95% CI −0.41 to 0.37, p = 0.1). Subgroup analyses also showed that the training background of participants (i.e., recreationally trained participants or professionally trained participants) and intervention duration (e.g., > or ≤six weeks) did not significantly affect the results. (4) Conclusions: This systematic review and meta-analysis provide evidence that compared to other dietary strategies, using LCHF with CT cannot induce greater benefits for lean mass, body fat percentage, body mass, VO2max, and aerobic performance in trained participants.
... More recently, Close et al. [10] re-iterated the need for carefully devised standardisation of dietary intake tailored to the measured outcome. Ideally, a dietary standardisation protocol should, where possible, consider individuals' habitual dietary practices and preferences in advance of an intervention [10,11,12,13]. Such consideration could contribute to greater adherence to the study protocol by research participants [14]. ...
... Since it has been shown that quality, quantity, timing, and distribution of protein intake per EO may alter muscle protein synthesis [6,8,19,22,23,24], energy and macronutrient composition per EO was standardised relative to body mass together with timing and distribution of EOs. In literature, dietary standardisation protocols have been proposed in nutrient plus exercise research investigating the effect of carbohydrate periodisation on performance in endurancetrained individuals and elite endurance athletes [11,25,26,27]. Similar to this research, the reported dietary standardisation in literature is based on participants' food preferences and is related to participants' body mass [25,26,27] or lean tissue mass [11,12]. ...
... In literature, dietary standardisation protocols have been proposed in nutrient plus exercise research investigating the effect of carbohydrate periodisation on performance in endurancetrained individuals and elite endurance athletes [11,25,26,27]. Similar to this research, the reported dietary standardisation in literature is based on participants' food preferences and is related to participants' body mass [25,26,27] or lean tissue mass [11,12]. In studies by Marquet et al. [26] and Louis et al. [25], the dietary standardisation protocol introduced the habituation phase before the one-week intervention and participants were given precise dietary guidelines of food allowances to meet daily and per EO recommended carbohydrate intake. ...
... With continued research in the field of diet and weight loss, the trend is starting to swing in the direction of low carbohydrate diets providing more prominent weight loss than traditional low-fat diets in both athletic and non-athletic populations [6,7] and therefore play an active role in a healthy lifestyle. Low carbohydrate and high fat diets have been shown to decrease basal glucose and insulin levels whilst increasing fat oxidation [8,9]. ...
... Whilst a large body of research conducted in weight loss has shown the benefits of the LCD compared with an LFD [7], there is still much debate over the efficacy of such a diet on sports performance. There is still a large body of work suggesting that carbohydrates are vital for energy output and improved performance [8,16,17]. These same studies also debunk the theory of a low carbohydrate and high fat diet being effective or equivalent to a high carbohydrate diet in performance. ...
... Consequently, athletes have been encouraged to carbohydrate load prior to competition and for recovery purposes to take full advantage of muscle glycogen stores [20,24]. Whilst this theory has been refined to adopt to the energy requirements of a given sport or task [8,[25][26][27], the theoretical underpinnings of exogenous carbohydrate ingestion for performance fuel has remained. This belief has become a staple in nutritional sports performance. ...
Article
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This paper reviews the literature in ketogenic diets and athletic performance. The review aims to compare, and contrast differing scientific opinions and gain a clearer understanding of the diet’s validity in athletic performance. The role of a low carbohydrate and high fat (LCHF) diet or ketogenic diet on athletic performance has created much debate in recent years. Evidence identifying that the diet fails to improve and rather diminishes performance has been discussed in literature, however advocates of the diet have found methodological flaws in research previously conducted. The purpose of this paper is to review literature surrounding the use of LCHF diets in sports performance and compare these reviews with previous literature on the efficacy of carbohydrates as a main fuel source. A total of 63 papers and scientific presentations were utilized for review. A large portion of research for the LCHF diets suggests an adaptation period lasting between 4 weeks to as high as 3 months is required before improvements start to be noticed. Studies follow a trend with improvements being more common over longer-term dietary interventions rather than short term investigations. Evidence continually shows improved fat oxidation on a LCHF; however, this phenomenon does not necessarily correlate with performance output with some investigations identifying reduced VO2max results. Alternatively, longer investigations have identified no difference between groups (i.e., no loss in performance) or in some cases an improved VO2max output. Results on power output have again showed interesting features with the diet being clearly advantageous for weight loss that is not associated with performance deterioration. Overall, the jury remains out over the effects of a diet of this nature, however there is room for collaboration between the low carbohydrate and high carbohydrate groups to create methodological sound studies that may shed more light on the actual benefits and detriments of such a diet.
... They acknowledged that differences in habitual diet might partially explain these different responses. Indeed, many publications now suggest that this "carbohydrate-dependence" may, at least in part, reflect a state of chronic adaptation to a high-carbohydrate low-fat (HCLF) diet that alters quite rapidly on exposure to a low-carbohydrate high-fat (LCHF) diet [24,[42][43][44][45][46]. ...
... Thus, has arisen the belief that exercise of high intensity is "carbohydrate dependent" [3,[19][20][21] and that "fat-derived ATP production is designed to provide a 'helper fuel' during exercise, with a maximum amount of energy at power outputs of ~60-65% VO 2 max [22]" [23]. As a result, "For most events at the Olympics, carbohydrate is the primary fuel for anaerobic and aerobic metabolism" [23] so that "when elite athletes train for and compete in most sporting events, carbohydrate fuels are the predominant and critical substrate for the working muscles, and the availability of carbohydrate [19,24] rather than fat, wins gold medals" [25]. ...
... However, this "carbohydrate dependence" can be readily modified with the adoption of a high-fat diet. This is not a novel finding, having been repeatedly shown in the past [42,43] and more recently [24,[44][45][46]. ...
Article
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Recently we reported similar performances in both progressive tests to exhaustion (VO2max) and 5km running time trials (5KTT) after consuming low-carbohydrate, high-fat (LCHF) or high-carbohydrate, low-fat (HCLF) diets. Accordingly, we tested the null hypothesis that the metabolic responses during both tests would be similar across diets. In a randomized, counterbalanced, cross-over design, seven male athletes (VO2max: 61.9 ± 6.1 mL/kg/min; age: 35.6 ± 8.4 years; height: 178.7 ± 4.1 cm; mass: 68.6 ± 1.6 kg; body fat: 5.0 ± 1.3%) completed six weeks of LCHF (6/69/25% energy carbohydrate/fat/protein) and HCLF (57/28/15% energy carbohydrate/fat/protein) diets, separated by a two-week washout. Substrate utilization and energy expenditure were measured during VO2max tests and 5KTTs. The LCHF diet markedly increased fat oxidation and reduced carbohydrate oxidation, with no associated impairment in either the VO2max tests or the 5KTTs. Following the LCHF diet, athletes generated 50% or more of their energy requirements from fat at exercise intensities up to 90% VO2max and reached the crossover point for substrate utilization at ~85% VO2max. In contrast, following the HCLF diet, carbohydrate provided more than 50% of the total energy consumption at all exercise intensities. During the 5KTT, ~56% of energy was derived from fat following the LCHF diet whereas more than 93% of the energy came from carbohydrate following the HCLF diet. This study provides evidence of greater metabolic flexibility following LCHF eating and challenges the popular doctrines of “carbohydrate dependence” for high intensity exercise and the role dietary macronutrients play in human performance.
... From a practical point of view, exercising after an overnight fast is one of several ways to reduce exogenous CHO availability for training, and it has been incorporated into periodized training nutrition programs (i.e., "train-low" or "train-high"), that aim to promote training-induced adaptations of skeletal muscle (i.e., increased rates of lipid oxidation and improved exercise capacity) [18][19][20]. Therefore, YM intake after an overnight fast might be a good additional strategy to increment FAT ox and help sustain performance [11][12][13] in the "train-low" context. ...
... Therefore, YM intake after an overnight fast might be a good additional strategy to increment FAT ox and help sustain performance [11][12][13] in the "train-low" context. However, "train-low" strategies are generally undertaken alongside deliberate training sessions with a high CHO availability period ("train-high") [18][19][20]. Hence, the potential ergogenic effects of YM [6,[11][12][13] should also be addressed in contexts that translate to practical sports strategies with high CHO intake, such as pre-exercise CHO meal [19]. ...
... § P < 0.05, compared with YMD-F at post-ex. TAC serum total antioxidant capacity, TOS serum total oxidant status, OSI oxidative stress index a good dietary strategy to help to maintain blood glucose during exercise performed in the fasted state [18][19][20]. The effect of YM on TT performance was first demonstrated by Areta et al. [12]. ...
Article
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Introduction The consumption of yerba mate (YM), a source of antioxidants, in a fasted state increases fatty acid oxidation (FAT ox ) during low–moderate-intensity exercise and improves performance in high-intensity exercise. However, the impact of a pre-exercise carbohydrate (CHO) meal on YM effects during exercise is unknown. Objective We investigated the effects of yerba mate drink (YMD) consumed in the fasted state (YMD-F) or after a CHO meal (YMD-CHO) on measurements of metabolism, performance, and blood oxidative stress markers in cycling exercise. Methods In a randomized, repeated-measures, crossover design, eight trained male cyclists ingested (i) YMD-CHO, (ii) YMD-F, or (iii) control-water and CHO meal (Control-CHO). The YMD (an infusion of 5 g of ultrarefined leaves in 250 mL of water) was taken for 7 days and 40 min before exercise. CHO meal (1 g/kg body mass) was consumed 60 min before exercise. The cycling protocol included a 40-min low-intensity (~ 53% V̇ O 2peak ) constant load test (CLT); a 20-min time trial (TT); and 4 × 10-s all-out sprints. Blood samples and respiratory gases were collected before, during, and/or after tests. Results During CLT, YMD-CHO increased FAT ox ~ 13% vs . YMD-F ( P = 0.041) and ~ 27% vs . Control-CHO ( P < 0.001). During TT, YMD-CHO increased FAT ox ~ 160% vs . YMD-F ( P < 0.001) and ~ 150% vs . Control-CHO ( P < 0.001). Power output during TT improved ~ 3% ( P = 0.022) in YMD-CHO vs . Control-CHO and was strongly correlated with changes in serum total antioxidant capacity ( r = −0.87) and oxidative stress index ( r = 0.76) at post-exercise in YMD-CHO. Performance in sprints was not affected by YMD. Conclusion CHO intake did not negate the effect of YMD on FAT ox or TT performance. Instead, a synergism between the two dietary strategies may be present. Clinical Trial Registration NCT04642144. November 18, 2020. Retrospectively registered.
... Within the last three decades, several studies have indicated an improved fat metabolism under resting and submaximal exercise conditions following longterm (! 2 weeks) high fat diets (Phinney et al. 1983;Lambert et al. 1994;Rowlands and Hopkins 2002;Zajac et al. 2014;Volek et al. 2016;Burke et al. 2017). However, in most studies with prolonged high fat diets, there was only a small positive (or even negative) effect on performance during competitioneven with a prior carbohydrate restoration phase to prevent low pre-competition glycogen storages (Burke 2015). ...
... Some studies confirmed, that a high fat diet has a positive impact on performance at submaximal intensities (Phinney et al. 1983;Lambert et al. 1994;Rowlands and Hopkins 2002). Despite an improved fat metabolism under resting conditions and during submaximal exercise, there is a growing body of evidence that these metabolic changes induced by ketogenic or nonketogenic high fat diets are not associated with an improved endurance performance e.g. during competition (Burke 2015;Burke et al. 2017;Zinn et al. 2017;Durkalec-Michalski et al. 2021). Although endurance competitions are predominantly characterised by submaximal intensities, high intensities (e.g. ...
... Previous studies investigating whether carbohydrate-rich diets are more advantageous to improve endurance performance than high fat diets have shown equivocal results (Lambert et al. 1994;Rowlands and Hopkins 2002;Burke et al. 2017). The carbohydrate-rich controls were not chosen by the quality of carbohydrate rather the quantity of ingested carbohydrates. ...
Article
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The present study investigated the effect of a 4-week high fat low carbohydrate (HFLC-G) versus high carbohydrate low glycaemic (LGI-G) or high glycaemic (HGI-G) diet on power output at lactate thresholds, peak oxygen uptake and peak performance during an incremental cycle test in 28 male endurance athletes. All participants showed improved levels of power output at the lactate thresholds with a more pronounced effect in the HFLC-G and LGI-G. In the HFLC-G peak performance (-11.6 ± 16.3 W) decreased, while in the LGI-G (9.20 ± 13.8 W) and HGI-G (9.89 ± 12.8 W) peak performance increased (p = 0.009). In summary, the LGI-G showed comparable training adaptations as the HFLC-G at submaximal intensities without limiting the ability to perform at high intensities. Compared to a HFLC and HGI diet, the LGI diet in this study seemed to be advantageous during submaximal and high intensities resulting from an improved metabolic flexibility.
... The literature search and selection of studies are presented in Figure 1. A total of 18 studies (Greenhaff, Gleeson, and Maughan 1988;Fleming et al. 2003;Edwards et al. 2011;Burke et al. 2017Burke et al. , 2020Cipryan et al. 2018;Greene et al. 2018;Kephart et al. 2018;McSwiney et al. 2018;Vargas et al. 2018Vargas et al. , 2020Dostal et ...
... Details of the general characteristics of included studies (Greenhaff, Gleeson, and Maughan 1988;Fleming et al. 2003;Edwards et al. 2011;Burke et al. 2017 Table 2, and characteristics of the dietary intervention studied are presented in Table 3. ...
... According to Rob 2 tool for RCTs, five studies were judged to be at high risk of bias due to deviations from the intended intervention and due to missing outcome data (Vargas et al. 2018(Vargas et al. , 2020Shaw et al. 2019;Sjödin et al. 2020;Wilson et al. 2020) (exclusion of participants in the intention-to-treat approach to statistical analysis (Vargas et al. 2018(Vargas et al. , 2020Shaw et al. 2019;Sjödin et al. 2020) or loss of participants who did not adhere to the intervention (Wilson et al. 2020)). Furthermore, four studies were judged to be at some concerns (Greenhaff, Gleeson, and Maughan 1988;Edwards et al. 2011;Prins et al. 2019;Wroble et al. 2019) due to bias arising from the randomization process (Greenhaff, Gleeson, and Maughan 1988;Edwards et al. 2011) According to ROBINS-I for NRCTs, two studies were judged to be at serious risk of bias (Fleming et al. 2003;Kephart et al. 2018) and six at moderate risk of bias (Burke et al. 2017(Burke et al. , 2020Cipryan et al. 2018;McSwiney et al. 2018;Dostal et al. 2019;LaFountain et al. 2019) due to confounding that for all studies were considered by authors, the performance level of the included participants of each study, presence of muscle or tissue injury during the study, the presence of participants already adept to KD and use of ergogenic resources (dietary supplementation and medication). One study (Kephart et al. 2018) was also judged to be at serious risk of bias due to the intervention classification because the control group did not have any diet specified. ...
Article
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.
... In the last decades, several studies have investigated the metabolic adaptations by long-term (≥2 weeks) HFLC diets. Various investigations (≥2 weeks) have identified an increased utilization of fats measured by decreased RER and lactate values and an increased fat oxidation during resting and submaximal exercise conditions (14,(32)(33)(34)(35)(36). In contrast, the carbohydraterich control diets were associated with the opposite effect (32,33,35). ...
... Various investigations (≥2 weeks) have identified an increased utilization of fats measured by decreased RER and lactate values and an increased fat oxidation during resting and submaximal exercise conditions (14,(32)(33)(34)(35)(36). In contrast, the carbohydraterich control diets were associated with the opposite effect (32,33,35). The reciprocal relationship between fat and carbohydrate oxidation in muscle at rest and during different exercise scenarios might be explained by higher plasma concentrations of free fatty acids, decreased insulin concentrations, and improved fat transportation via fatty acid translocase FAT/CD36 protein across the cell membrane resulting from an increased fat intake (2,3). ...
... However, the benefits of a low carbohydrate diet can be rather attributed to the relatively high protein content, but not the relatively lower carbohydrate content (45,46). In a recent study with athletes, different approaches (high vs. low fat) but similar protein intakes resulted in a similar change of body composition (mean loss in body fat was 1.4 kg) (32). These are in accordance with a meta-analysis examining the impact of different diet types in obese or overweight people (47). ...
Article
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Consuming low glycemic carbohydrates leads to an increased muscle fat utilization and preservation of intramuscular glycogen, which is associated with improved flexibility to metabolize either carbohydrates or fats during endurance exercise. The purpose of this trial was to investigate the effect of a 4-week high fat low carbohydrate (HFLC-G: ≥65% high glycemic carbohydrates per day; n = 9) vs. high carbohydrate low glycemic (LGI-G: ≥65% low glycemic carbohydrates daily; n = 10) or high glycemic (HGI-G: ≥65% fat, ≤ 50 g carbohydrates daily; n = 9) diet on fat and carbohydrate metabolism at rest and during exercise in 28 male athletes. Changes in metabolic parameters under resting conditions and during cycle ergometry (submaximal and with incremental workload) from pre- to post-intervention were determined by lactate diagnostics and measurements of the respiratory exchange ratio (RER). Additionally, body composition and perceptual responses to the diets [visual analog scale (VAS)] were measured. A significance level of α = 0.05 was considered. HFLC-G was associated with markedly decreased lactate concentrations during the submaximal (−0.553 ± 0.783 mmol/l, p = 0.067) and incremental cycle test [−5.00 ± 5.71 (mmol/l) × min; p = 0.030] and reduced RER values at rest (−0.058 ± 0.108; p = 0.146) during the submaximal (−0.078 ± 0.046; p = 0.001) and incremental cycle test (−1.64 ± 0.700 RER × minutes; p < 0.001). In the HFLC-G, fat mass (p < 0.001) decreased. In LGI-G lactate, concentrations decreased in the incremental cycle test [−6.56 ± 6.65 (mmol/l) × min; p = 0.012]. In the LGI-G, fat mass (p < 0.01) and VAS values decreased, indicating improved levels of gastrointestinal conditions and perception of effort during training. The main findings in the HGI-G were increased RER (0.047 ± 0.076; p = 0.117) and lactate concentrations (0.170 ± 0.206 mmol/l, p = 0.038) at rest. Although the impact on fat oxidation in the LGI-G was not as pronounced as following the HFLC diet, the adaptations in the LGI-G were consistent with an improved metabolic flexibility and additional benefits regarding exercise performance in male athletes.
... Over the past 7 years, Professor Louise Burke and her team have conducted a series [134][135][136] of quite remarkable studies of the effects of different dietary interventions on Olympic race walkers. The studies are exceptional because they involve world-class athletes and have provided a wealth of unique metabolic data that are of the greatest value. ...
... First, elite athletes preparing for Olympic competition cannot be expected to commit to randomization to a novel diet, that is, to participate in a randomized controlled trial (RCT). The authors explained: "The design and implementation of the study involved a pragmatic blend of rigorous scientific control and research methodology with real-world allowances needed to accommodate elite athlete populations" [134]. ...
... Thus: "Prior to their arrival to the study camps, participants were educated about the benefits and limitations of the different dietary treatments and asked to nominate their preference(s) for, or non-acceptance of, each of these interventions" [134]. ...
Article
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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.
... To support that, it has been shown previously that nutritional status and high carbohydrate availability maintained several days before the prolonged exercise bout seem to prevent the loss of efficiency (Cole et al. 2014;Dumke et al. 2007) suggestive of maintained metabolic efficiency. In contrast, when pre-exercise low-glycogen state is achieved through chronic dietary manipulation (e.g., LCHF or ketogenic diet) the loss of exercise economy at submaximal speeds has been reported in race walkers and runners (Burke et al. 2017;Shaw et al. 2019). Shaw et al. (2019) demonstrated an increased oxygen cost at intensities > 70% V O 2max (measured at running velocities of 12 and 13.5 km h −1 ) after 31 days on a ketogenic diet, and this increase was only partially explained by shifts in RER. ...
... Shaw et al. (2019) demonstrated an increased oxygen cost at intensities > 70% V O 2max (measured at running velocities of 12 and 13.5 km h −1 ) after 31 days on a ketogenic diet, and this increase was only partially explained by shifts in RER. Likewise, Burke et al. (2017) also showed reduced economy in elite racewalkers after 3-weeks of intensified training and ketogenic diet consumption, at speeds corresponding to 50 km and 20 km race pace (~ 75% and ~ 90% V O 2max , respectively). In summary, it seems that maintaining high carbohydrate and glycogen availability before the start of prolonged and intense exercise bout is an important aspect of preventing the loss of exercise efficiency. ...
Article
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Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr⁻¹) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS V˙O2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{{2}}$$\end{document}, HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s⁻¹) existed in PLA after the 1st (Δ − 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ − 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.
... There is some evidences that KD positively increase VO 2 max in normoxic conditions (19,(23)(24)(25)(26), but this aspect has never been explored in hypoxic condition. However, subjective bene t of high fat diet in high altitude was praised by the extreme high-altitude mountaineer Erhard Loretan, e.g. at Everest base camp in 1986. ...
... We noticed no performance marker which is systematically affected by ICKD. This recorded improvement has been similarly partially reported in normoxia (17,25). VO 2 max re ects the cardiorespiratory tness(46) and is considered as a gold standard for measuring aerobic metabolism (47). ...
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Background: Ketogenic diet (KD) reduces carbohydrate (CHO) daily ingestion replacing majority of calories by fat. KD is of increasing interest among athletes for evidence about VO2max increment. This is the principal performance limitation in high altitude. We so examine the tolerance of a 4-week isocaloric ketogenic diet (ICKD) under simulated hypoxia, the possibility of evaluating participant’s ICKD performances benefit by a maximal graded exercise bike test in hypoxic condition and assess data on its effect on performance markers and arterial blood gases. Methods: Using a randomised single blind cross-over model, 6 recreational mountaineers (24 to 44 years) completed a 4-week ICKD either followed or preceded by a 4-week habitual mixed western diet (HD). Performance parameters (VO2max, lactate threshold (LT), peak power (Ppeak)) and arterial blood gases (PaO2, PaCO2, pH, HCO3⁻) were measured at baseline under two conditions (normoxia and hypoxia) as well as post 4-week HD and post 4-week ICKD under hypoxic condition. Results: We analysed data of 6 participants. Hypoxia led to a decreased performance in all participants. ICKD diet decreased their PaO2 by -14.5% and increased their VO2max by +7.3% and Ppeak by +4.7%. Conclusion: All participants except one could complete the ICKD. VO2max improved with ICKD under the hypoxia condition. ICKD is thus an interesting alternative to CHO dependency for endurance performances at high-altitude (1500-3500 m) including high-altitude training sessions and high-altitude races. Nevertheless, the PaO2 decrement with ICKD remains a significant limitation of ICKD in very high- to extreme-altitude (>3500 m.). Trial registration: CER-VD, 2020-00427. Registered 18.08.2020 - Prospectively registered
... Since the primary benefit of a KD is to enhance mitochondrial mass and function-we will focus our discussion on endurance performance since mitochondria play a greater role in this type of sport. The data to date in this area indicates that there is either no additional benefit or an impairment in elite performance when athletes train on a KD (10). Chief among these studies are Prof. ...
... The generation of ATP from fat oxidation normally declines as exercise intensity increases (53) and this has been attributed to the inability to A C C E P T E D efficiently transport fatty acids into the mitochondria during higher levels of exercise intensity (greater than ~65% VO 2max ). Even if fatty acid transport was not limiting, endurance athletes on a KD would require significantly more oxygen to perform at the same power or velocity when compared with athletes on a carbohydrate based diet (10). Since economy, the volume of oxygen needed to maintain a specific power or speed, is directly related to performance, this would suggest that a KD would limit high end performance. ...
Article
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As humans age, we lose skeletal muscle mass, even in the absence of disease (sarcopenia), increasing the risk of death. Low mitochondrial mass and activity contributes to sarcopenia. It is our hypothesis that, a ketogenic diet improves skeletal muscle mitochondrial mass and function when they have declined due to aging or disease, but not in athletes where mitochondrial quality is high.
... Attempts to replace the muscle's reliance on the relatively finite body CHO stores have been shown to achieve dramatic alterations to muscle substrate use. Indeed, adaptation to low CHO, high fat (LCHF) diets (~65% fat, <2.5 g·kg −1 ·day −1 CHO) [3], and more topically, their ketogenic counterparts (~80% fat, <50 g CHO·day −1 ), can double the already enhanced rates of fat oxidation in highly trained endurance athletes to mean maximal rates of~1.5 g·min −1 , shifting the intensity at which this occurs from~45% to~70% of maximal aerobic capacity [4][5][6]. However, at the intensities at which competitive endurance events are conducted, such increases in fat utilisation do not translate to performance improvements [5][6][7]; indeed, they are harmful to sustained speed or power output, possibly due to the increased oxygen cost associated with fat oxidation (for review, see Burke [8]). ...
... Indeed, adaptation to low CHO, high fat (LCHF) diets (~65% fat, <2.5 g·kg −1 ·day −1 CHO) [3], and more topically, their ketogenic counterparts (~80% fat, <50 g CHO·day −1 ), can double the already enhanced rates of fat oxidation in highly trained endurance athletes to mean maximal rates of~1.5 g·min −1 , shifting the intensity at which this occurs from~45% to~70% of maximal aerobic capacity [4][5][6]. However, at the intensities at which competitive endurance events are conducted, such increases in fat utilisation do not translate to performance improvements [5][6][7]; indeed, they are harmful to sustained speed or power output, possibly due to the increased oxygen cost associated with fat oxidation (for review, see Burke [8]). Empirical evidence of the reduction in exercise economy associated with adaptation to ketogenic LCHF diets has led to calculations of theoretical advantages to economy and performance following further increases in the contribution of CHO to exercise substrate use [2]. ...
Article
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We implemented a multi-pronged strategy (MAX) involving chronic (2 weeks high carbohydrate [CHO] diet + gut-training) and acute (CHO loading + 90 g·h −1 CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON) in two groups of athletes. Nineteen elite male race walkers (MAX: 9; CON:10) undertook a 26 km race-walking session before and after the respective interventions to investigate gastrointestinal function (absorption capacity), integrity (epithelial injury), and symptoms (GIS). We observed considerable individual variability in responses, resulting in a statistically significant (p < 0.001) yet likely clinically insignificant increase (∆ 736 pg·mL −1) in I-FABP after exercise across all trials, with no significant differences in breath H 2 across exercise (p = 0.970). MAX was associated with increased GIS in the second half of the exercise, especially in upper GIS (p < 0.01). Eighteen highly trained male and female distance runners (MAX: 10; CON: 8) then completed a 35 km run (28 km steady-state + 7 km time-trial) supported by either a slightly modified MAX or CON strategy. Inter-individual variability was observed, without major differences in epithelial cell intestinal fatty acid binding protein (I-FABP) or GIS, due to exercise, trial, or group, despite the 3-fold increase in exercise CHO intake in MAX post-intervention. The tight-junction (claudin-3) response decreased in both groups from pre-to post-intervention. Groups achieved a similar performance improvement from pre-to post-intervention (CON = 39 s [95 CI 15-63 s]; MAX = 36 s [13-59 s]; p = 0.002). Although this suggests that further increases in CHO availability above current guidelines do not confer additional advantages, limitations in our study execution (e.g., confounding loss of BM in several individuals despite a live-in training camp environment and significant increases in aerobic capacity due to intensified training) may have masked small differences. Therefore, athletes should meet the minimum CHO guidelines for training and competition goals, noting that, with practice, increased CHO intake can be tolerated, and may contribute to performance outcomes.
... The RE is also affected by diet. Three weeks of intense training combined with a low-carb, high-fat ketogenic diet, in elite runners, despite an increase in peak aerobic capacity, impairs performance due to a reduction in RE (17). Indeed, if such a diet increases the ability of muscle to use fat as a substrate, keto-adaptation reduces muscle oxidation of carbohydrates and the ability to use glycogen, a limitation in high intensity endurance exercise (18). ...
... Indeed, if such a diet increases the ability of muscle to use fat as a substrate, keto-adaptation reduces muscle oxidation of carbohydrates and the ability to use glycogen, a limitation in high intensity endurance exercise (18). A chronic or periodised high carbohydrate availability, on the other hand, improves running performance, due to a reduced oxidative demand of the glycemic substrate (17). ...
... A high-fat diet may be challenging to adhere to and can cause gastrointestinal distress for some athletes(Pfeiffer et al. 2012). Moreover, high-fat diets may not provide sufficient carbohydrates to meet the demands of high-intensity exercise and may compromise recovery[24]. ...
Article
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This literature review analyzed 20 studies (n=147) investigating the effects of a high-fat diet on ultrarunning performance and metabolism. Results suggest that a high-fat diet can improve fat oxidation during exercise and may improve ultrarunning performance in some cases, although the effects on performance and metabolic markers appear to be highly variable. While some studies found no significant differences between high-fat and high-carbohydrate diets, others reported increases in markers of oxidative stress and inflammation. Additionally, several studies found that a very low-carbohydrate, high-fat diet could decrease muscle glycogen levels, which could potentially have negative effects on performance. Overall, these findings suggest that a high-fat diet may have some benefits for ultrarunners, but the optimal macronutrient ratio for maximizing performance remains unclear. Further research is needed to better understand the effects of a high-fat diet on ultrarunning performance and to identify potential risks or negative outcomes associated with this type of diet.
... Jak je nám již známo, i z tohoto výzkumu vyplynulo, že adaptace na ketogenní dietu výrazně zvýšila rychlost oxidace tuku v celém těle během cvičení. Na rozdíl od tréninků, při závodech a vytrvalostních závodech, adaptace na nízkosacharidovou stravu zhoršuje výkon, a to i přes výrazné zlepšení aerobní kapacity (Burke et al. 2017). ...
Thesis
Ketogenní dieta je dieta s vysokým obsahem tuků, značným množstvím bílkovin a nízkým obsahem sacharidů. Dieta se využívá jako nástroj k léčbě epileptických záchvatů a v dnešní době v hojné míře k redukci hmotnosti a změně životního stylu, na základě mechanismu ketogeneze. Okolo pojmu ketodieta panuje velké množství otázek a rozporuplných názorů jak odborníků, tak široké veřejnosti. Můžeme pozorovat více forem nízkosacharidových diet, ale už je složité se dopátrat, na jakém principu dieta reálně funguje a jak na ni tělo může reagovat. Celá tato moderní dieta se prakticky točí okolo lipidů. O tom, jak tuky v těle fungují, už není kolikrát v brožurách o dietě či na stránkách zmíněno, a pokud člověk či pacient mění životní styl, měl by vědět, jak tento makronutrient funguje. Většina laické veřejnosti si spojuje energii se sacharidy neboli cukry, ale tato informace může být mírně zavádějící, jelikož sacharidy se nejdřív musí rozložit, aby z nich energie ve formě adenosintrifosfátu, zkráceně ATP, byla získána. Látková přeměna neboli metabolismus, probíhá i u lipidů s tím rozdílem, že 1 g tuku poskytne zhruba 2x víc energie než 1 g cukru. Děje se to v případě, že tělo velmi sníží nebo vyčerpá svoje zásoby sacharidů ve formě glykogenu, což je polysacharid, který slouží v těle živočichů jako energetická zásoba. Smyslem této bakalářské práce bylo shromáždit názory, fakta a informace týkající se funkčnosti ketogenní diety. Zjistit vědecky podložené názory odborníků na její pozitivní či negativní vliv na lidský organismus a tím i vyvrátit mýty, které ve společnosti kolují. Rozebrat proces lipidů v těle a poukázat na potencionální hrozby, které by se při nesprávném užívání mohly dostavit. Při standardním stravování, je paleta potravin velmi široká. Při nízkosacharidové dietě se ale jejich výběr zúží, a to o všechny potraviny s vysokou či střední koncentrací sacharidů. Je důležité zmínit, že v dnešní době jsou velmi populární instantní podoby stravy, před kterými nemalá část nutričních terapeutů varuje. Pokud je ale jídelníček správný a pacient je pod dohledem kvalifikovaných odborníků, je dokázáno, že tato dieta může být jak součástí léčebního procesu, tak pomocníkem při redukci hmotnosti.
... Unfortunately, sustained reliance on glycogen can result in glycogen depletion and lead to fatigue and decreased exercise capacity. Maximizing fat mobilization and oxidation and slowing glycogen depletion may improve performance at various exercise intensities [8,9]. ...
Article
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Wild blueberries (WBs) have been documented to decrease oxidative stress in active and sedentary populations as well as influence lipolytic enzymes and increase the rate of fat oxidation (FAT-ox) during rest. To examine the effect of WBs on the rate of FAT-ox and lipid peroxidation during submaximal exercise, 11 healthy, aerobically trained males (26 ± 7.5 years, 74.9 ± 7.54 kg, 10.5 ± 3.2% BF) completed a 2-week washout avoiding foods high in anthocyanins, then completed a control exercise protocol cycling at 65% of VO2peak for 40 min. Participants then consumed 375 g/d of anthocyanins for two weeks before repeating the exercise protocol. WBs increased FAT-ox when cycling at 65% of VO2peak by 19.7% at 20, 43.2% at 30, and 31.1% at 40 min, and carbohydrate oxidation (CHO-ox) decreased by 10.1% at 20, 19.2% at 30, and 14.8% at 40 min of cycling at 65% of VO2peak. Lactate was lower with WBs at 20 (WB: 2.6 ± 1.0, C: 3.0 ± 1.1), 30 (WB: 2.2 ± 0.9, C: 2.9 ± 1.0), and 40 min (WB: 1.9 ± 0.8, C: 2.5 ± 0.9). Results indicate that WBs may increase the rate of FAT-ox during moderate-intensity activity in healthy, active males.
... Dietary intake studies with low-carbohydrate, high-fat diets reported enhanced wholebody fat oxidation in elite race walkers [7]. However, the observations of impaired exercise performance with low-carbohydrate, high-fat diets [7,8] may have dampened the interest of it being a popular nutritional strategy among elite ultra-endurance athletes [9,10]. In ultraendurance athletes, dietary and training practices are expected to optimize the required physiological and structural adaptations that may minimize or even discount the effectiveness of dietary supplements that may affect substrate oxidation. ...
Article
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Physical training for ultra-endurance running provides physiological adaptations for exercise-induced substrate oxidation. We examined the effects of New Zealand blackcurrant (NZBC) extract on running-induced metabolic and physiological responses in a male amateur ultra-endurance runner (age: 40 years, body mass: 65.9 kg, BMI: 23.1 kg·m−2, body fat: 14.7%, V˙O2max: 55.3 mL·kg−1·min−1, resting heart rate: 45 beats·min−1, running history: 6 years, marathons: 20, ultra-marathons: 28, weekly training distance: ~80 km, weekly running time: ~9 h). Indirect calorimetry was used and heart rate recorded at 15 min intervals during 120 min of treadmill running (speed: 10.5 km·h−1, 58% V˙O2max) in an environmental chamber (temperature: ~26 °C, relative humidity: ~70%) at baseline and following 7 days intake of NZBC extract (210 mg of anthocyanins·day−1) with constant monitoring of core temperature. The male runner had unlimited access to water and consumed a 100-kcal energy gel at 40- and 80 min during the 120 min run. There were no differences (mean of 8, 15 min measurements) for minute ventilation, oxygen uptake, carbon dioxide production and core temperature. With NZBC extract, the respiratory exchange ratio was 0.02 units lower, carbohydrate oxidation was 11% lower and fat oxidation was 23% higher (control: 0.39 ± 0.08, NZBC extract: 0.48 ± 0.12 g·min−1, p < 0.01). Intake of the energy gel did not abolish the enhanced fat oxidation by NZBC extract. Seven days’ intake of New Zealand blackcurrant extract altered exercise-induced substrate oxidation in a male amateur ultra-endurance runner covering a half-marathon distance in 2 h. More studies are required to address whether intake of New Zealand blackcurrant extract provides a nutritional ergogenic effect for ultra-endurance athletes to enhance exercise performance.
... Although these effects have been shown to prevent performance decline in later stages of repeated high-intensity movements, in which aerobic metabolism becomes more important [20,21]. Other studies have shown that the effects negate benefits in athletic performance, in part due to reduced exercise economy [22,23]. In terms of fluid intake, it is not only necessary to offset the negative effect of dehydration on performance [24,25] but is important in macronutrient metabolism as glycogen is stored in human muscle bound to water in a proportion of 1:3 g [17]. ...
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Overtraining may affect the majority of elite athletes at least once in their career, the pathophysiology is however, not clearly understood. This study investigated dietary patterns in adolescent sprinters by comparing athletes who maladapted to prior training with these who adapted, to identify underlying triggers of overtraining. Food diaries were completed by participants during different training phases over 26 weeks. Participants were classified as non-athletes (NA, n = 13), maladapted (MA, n = 12) and adapted (AA, n = 20) athletes. Total energy (p < 0.001), protein (p = 0.009) and carbohydrates (p < 0001) intakes changed across the different training phases. Compared to AA, MA showed a decrease in total energy (p = 0.009) and carbohydrates (p < 0.001) intake throughout the season. Similarly, compared to NA, MA showed a decrease in total energy (p = 0.005) and carbohydrate (p < 0.001) intake across the season. A combination of total energy and carbohydrates intake, sleep quality, and training load/volume were assessed in a logistic regression model, energy intake (OR/CI: 4.7 (1.4, 9.3), p < 0.001), carbohydrates intake (OR/CI: 14.6 (10.0, 21.4), p < 0.001), and sleep quality (OR/CI: 2.8 (1.9, 4.8), p = 0.014) explained overtraining beyond the training load/volume in cases. Reduced total energy, carbohydrates intake, and sleep quality are likely triggers of overtraining beyond long intense training. Caloric and macronutrients periodization as a part of training could prevent maladaptation to training in adolescent sprinters.
... Bergström et al. (1967) in which 3 days of a low carbohydrate diet following quadriceps femoris muscle glycogen depletion in nine healthy subjects led to diminished glycogen regeneration and cycling performance compared to a mixed diet, while a high-carbohydrate diet induced a supercompensation of glycogen stores and significantly prolonged cycling duration. However, several studies allowing for a longer adaption period have shown no negative effects of low-carbohydrate diets on exercise performance in endurance (Phinney et al., 1983;Prins et al., 2019), strength/power (Gregory et al., 2017;Kephart et al., 2018;Paoli et al., 2012;Wilson et al., 2020) and team (Paoli et al., 2021) sports, although some studies found declines in competitive endurance performance (Burke et al., 2017;Zinn et al., 2017). It also appears that training in a glycogen-depleted state can result in favorable training adaptions (Impey et al., 2018). ...
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Objectives: In a recent paper, Hardy et al. (2022, Journal of Human Evolution 162: 103105) claim that the physiological Neanderthal requirement for plant carbohydrates may have reached 50%-60% of caloric intake, inferred from modern dietary guidelines and a putative need for high carbohydrate intake in pregnant/breastfeeding women and athletes. The aim of this article is to critically reexamine these arguments under the premise that hominins could adapt to hypercarnivorous diets and low carbohydrate consumption. Materials and Methods: Literature on ketogenic and carnivore diets was retrieved. A case report of a male rugby player voluntarily undertaking a carnivore diet under medical supervision is presented. Results: Human metabolism is highly flexible towards adapting to long-term low carbohydrate intakes by producing and utilizing ketone bodies. The evidence base of dietary guidelines is weak, and carbohydrate intake recommendations for athletes and during pregnancy/lactation are uncertain, making a translation to Neanderthal diets questionable. The studied rugby player maintained his sports performance and health over a 4-months period despite minimal carbohydrate intake. Discussion: Human physiology appears to have an extraordinary ability to utilize ketone bodies as a fuel for the brain and skeletal muscle, in particular also during exercise. The translation of dietary guidelines to Neanderthals and interpretation of studies in subjects not adapted to ketosis may be biased by a "glucocentric" perspective supposing that high carbohydrate intake is necessary for maintaining health. Allowing for the possibility of keto-adaption leads to a more coherent integration of archeological and physiological data. K E Y W O R D S carnivore diet, exercise nutrition, ketosis, paleolithic diet, pleistocene
... However, this is associated with increased oxygen consumption and reduced exercise economy, which may partially explain the loss of performance at higher exercise intensities. Due to a lack of evidence, low-carbohydrate and high-fat diets are not recommended for football players [32]. ...
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It is said that football matches are the second most important thing in the world. Football is currently one of the most popular sports and brings record numbers of people together in stadiums and in front of TV sets. For many years, players were allowed to consume the products they preferred at the times they subjectively deemed appropriate. However, today's soccer has evolved due to self-improvement and players following elite athletes. This change in approach to the sport has coincided with an increase in the pace and intensity of top soccer games over the past two decades. In addition, the commercialization of the sport has resulted in increasing demands and continually increasing the level of sportsmanship. Nutrition is an important part of the sports training program. International guidelines, based on scientific research, recommend amounts, types and timing of food intake to ensure excellent training while reducing injuries and trauma. In order to achieve metabolic optimization, there must be a balance between nutrition, training, and recovery. Energy should be provided from optimal sources, and maintaining an adequate energy balance is critical for those who engage in physical activity, especially professional athletes. Supplements and foodstuffs for special nutritional purposes are widely used, so knowledge of the indications for their use, as well as the risks posed by inappropriate use, is essential.
... This apparent incongruency may be due to the fact that a diet characterized by reduced relative carbohydrate intake, and thus increased relative fat and protein intake, takes several weeks to become accustomed to. In earlier studies, this switch from carbohydrate to fatderived fuels has been associated with reduced energy levels and general well-being (Burke et al., 2017;Phinney et al., 1983). ...
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The risk for development of non-communicable diseases (NCD’s) can be predicted by somatic or mental symptoms and dietary alterations aimed at improvement of those symptoms could potentially delay development of NCD’s. The goal of this study was to identify whether self-initiated dietary changes could improve mental and somatic symptoms in relatively healthy individuals. Participants (n=494) recruited from the Dutch population filled out weekly questionnaires on dietary intake, somatic and mental symptoms and physical activity for four weeks. There was a significant reduction in mental and somatic symptoms, body weight, and waist circumference at four weeks, whereas physical activity remained unchanged. Five dietary patterns were identified by principal component analysis labelled “Processed foods”, “Animal source foods”, “Wheel of Five”, “Traditional Dutch”, and “Party”. Reduction in mental symptoms was correlated to increased physical activity and reduced intake of Processed foods. Reduction in somatic symptoms was related to body weight loss and changes in dietary intake, less Processed foods, more Wheel of Five foods, reduced caloric intake, lower carbohydrate and higher fat intake. Other observed dietary changes were not correlated to changes in symptoms. In conclusion this research showed that a self-initiated dietary change can lead to a significant reduction of mental and somatic symptoms.
... Along with this, the expression of pyruvate dehydrogenase kinase 4 (PDK4), which contributes to PDH phosphorylation and impaired glucose utilization, also increased 2.2-, 2.8-, and 3.8-fold in skeletal muscles (gastrocnemius, tibialis anterior, and soleus, respectively) after KD [54]. An increase in PDK4 content in skeletal muscle was repeatedly confirmed after KD [59,60] as well as KD-induced decline in carbohydrate utilization capacity during exercise [61][62][63], indicating that muscle tissue after KD shifted the preferred energy substrate from glucose to fat. It was shown that KD with a medium-chain triglyceride (MCT) content increased the ketolytic capacity in skeletal muscle without exerting inhibitory effects on carbohydrate metabolism [64] in contrast to long-chain triglyceride (LCT) content. ...
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Dietary intervention is widely used as a therapeutic approach ranging from the treatment of neurological disorders to attempts to extend lifespan. The most important effect of various diets is a change in energy metabolism. Since muscles constitute 40% of total body mass and are one of the major sites of glucose and energy uptake, various diets primarily affect their metabolism, causing both positive and negative changes in physiology and signaling pathways. In this review, we discuss changes in the energy metabolism of muscles under conditions of the low-carbohydrate, high-fat diet/ketogenic diet (KD), fasting, or administration of exogenous ketone bodies, which are all promising approaches to the treatment of various diseases. KD’s main influence on the muscle is expressed through energy metabolism changes, particularly decreased carbohydrate and increased fat oxidation. This affects mitochondrial quantity, oxidative metabolism, antioxidant capacity, and activity of enzymes. The benefits of KD for muscles stay controversial, which could be explained by its different effects on various fiber types, including on muscle fiber-type ratio. The impacts of KD or of its mimetics are largely beneficial but could sometimes induce adverse effects such as cardiac fibrosis.
... The transition from carbohydrate to fat utilization at higher exercise intensities promotes glycogen sparing and improved makers of aerobic performance; however, this has not shown to improve competition outcomes. [22] Although there is theoretical rationale for employing carbohydrate restriction in endurance sports, the prevalence of previous carbohydrate restriction in our group of female athletes is likely because female athletes in our study were predominately runners. As previously discussed, thinner figure is often more desirable for runners. ...
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Background Frequent dieting is common in athletes attempting to achieve a body composition perceived to improve performance. Excessive dieting may indicate disordered eating (DE) behaviors and can result in clinical eating disorders. However, the current nutrition patterns that underly dieting culture are underexplored in endurance athletes. Therefore, the purpose of this study was to identify the sex differences in nutrition patterns among a group of endurance athletes. Methods Two-hundred and thirty-one endurance athletes (females = 124) completed a questionnaire regarding their dieting patterns and associated variables. Results The majority of athletes did not follow a planned diet (70.1%). For endurance athletes on planned diets (n = 69), males were more likely follow a balanced diet ( p = 0.048) and females were more likely to follow a plant-based diet ( p = 0.021). Female endurance athletes not on a planned diet (n = 162) were more likely to have attempted at least one diet ( p < 0.001). Male athletes attempted 2.0 ± 1.3 different diets on average compared to 3.0 ± 2.0 for females ( p = 0.002). Female athletes were more likely to attempt ≥ three diets ( p = 0.022). The most common diet attempts included carbohydrate/energy restrictive, plant-based, and elimination diets. Females were more likely to attempt ketogenic ( p = 0.047), low-carbohydrate ( p = 0.002), and energy restricted diets ( p = 0.010). Females made up the entirety of those who attempted gluten-/dairy-free diets (F = 22.0%, M = 0.0%). Conclusions Being a female athlete is a major determinant of higher dieting frequency and continual implementation of popular restrictive dietary interventions. Sports dietitians and coaches should prospectively assess eating behavior and provide appropriate programming, education, and monitoring of female endurance athletes.
... Moreover, low carbohydrate availability has also been linked to decrements in sport performance (4) and lower levels of luteinizing hormone, triiodothyronine (T3), and leptin (28). Therefore, maintaining carbohydrate availability is especially important during periods of energy restriction and negative EB (4). Aside from detrimental effects on strength and performance (24), prolonged periods of negative EB are also likely to cause a reduction in FFM (20). ...
Article
Monedero, J, Duff, C, and Egan, B. Dietary intakes and the risk of low energy availability in male and female advanced and elite rock climbers. J Strength Cond Res XX(X): 000–000, 2022—There is a culture among rock climbers of striving to maintain low body mass and percentage body fat to enhance performance. Diet practices based on this belief might lead to increased risk of low energy availability (LEA) or eating disorders (EDs). Twenty-five advanced or elite rock climbers (male, n = 14; female, n = 11) had body composition measured, completed 4-day food intake and physical activity diaries while wearing an accelerometer and heart rate monitor, and completed the Eating Attitudes Test (EAT)-26 and the Low Energy Availability in Females Questionnaire (LEAF-Q; n = 11 female subjects only). EAT-26 scores of 3.5 (1.8, 7.0) [median (IQR)] and 9.3 ± 6.4 (mean ± SD) for male and female subjects, respectively, indicated low risk of ED in this cohort, but 4 female subjects were at high risk of LEA according to LEAF-Q scores. Suboptimal (<45 kcal·kg·FFM−1·d−1) and LEA (<30 kcal·kg·FFM−1·d−1) were evident in 88 and 28%, respectively, of climbers. However, only the female climbers had energy intakes (1775 ± 351 kcal·d−1) significantly lower than their calculated energy requirements (2056 ± 254 kcal·d−1; p = 0.006). In all subjects, carbohydrate intakes were lower (male subjects: 3.8 ± 1.2 g·kg−1·d−1, p = 0.002; female subjects: 3.4 ± 0.7 g·kg−1·d−1, p < 0.001), and fat intakes were higher (male subjects: 1.6 ± 0.5 g·kg−1·d−1, p < 0.001; female subjects: 1.4 ± 0.4 g·kg−1·day−1, p < 0.001) than current sports nutrition recommendations, and inadequate intakes of calcium, magnesium, and vitamin D were observed. Female subjects specifically had lower than recommended intakes of protein and iron. These results show that advanced and elite rock climbers have a high prevalence of LEA and have a risk of having nutritional deficiencies as result of their diet.
... Furthermore, the literature is still uncertain whether [37][38][39][40] or not ketogenic diets negatively affect the ability to perform regular exercise, i.e., the typical wide-range rehabilitation tool playing an essential role in the management of overweight people with T2DM or other metabolic dysfunctions [35,36]. Appropriate rehabilitation programs rely on suitable, personalized exercise types and duration sessions [41,42]. ...
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Several studies have shown a strong correlation between the different types of diets and gut microbiota composition on glycemia and weight loss. In this direction, low-carbohydrate and ketogenic diets have gained popularity, despite studies published so far leading to controversial results on subjects with diabetes. In this narrative review, firstly, we aimed to analyze the role of very-low-calorie ketogenic diets (VLCKDs) in type 2 diabetes (T2DM) and obesity management. Secondly, in this context, we focused attention on gut microbiota as a function of VLCKD, particularly in T2DM and obesity treatment. Finally, we reported all this evidence to underline the importance of gut microbiota to exalt new nutritional strategies for “tailor-made” management, treatment, and rehabilitation in subjects with T2DM and obesity, even with diabetic complications. In conclusion, this narrative review outlined the beneficial impact of VLCKD on gut microbiota even in subjects with T2DM and obesity, and, despite inner VLCKD short-duration feature allowing no sound-enough provisions for long-term outcomes, witnessed in favor of the short-term safety of VLCKD in those patients. Level of evidence Level V: Opinions of authorities, based on descriptive studies, narrative reviews, clinical experience, or reports of expert committees.
... For example, limitations of the capacity for CHO oxidation appear to be a reciprocal outcome of fat adaptation protocols (Helge, 2000), and the latter thus impairs performance at higher intensities (Burke et al., 2017). This uncertainty suggests that fat adaptation strategies, with or without the acute restoration of CHO availability, are less suited to performance goals of endurance athletes who need to undertake the whole, or critical parts, of their event in such high-intensity domains. ...
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This study was designed to test whether adaptation to a CHO-restricted diet affects physical capacity during prolonged exercise. It is hypothesised that chronically reducing an individual's dietary carbohydrate intake during training will increase their ultra-endurance exercise capacity compared to a chronic high carbohydrate diet. Thirteen highly trained endurance athletes (eight males, VO2max 66.0 ± 9.5 ml/kg/min, five females VO2max 50.6 ± 8.4 ml/kg/min) consumed a moderate (>5 g CHO/kg/day) and a low (<2 g CHO/kg/day) carbohydrate training diet for four weeks in a randomized cross-over design. Performance was measured after a 24 h high carbohydrate "loading" regime, through a self-paced time trial to complete a fixed workload equivalent to five hours at a workload calculated to elicit 55% VO2max. Although time to completion was not significantly different between diets, the average absolute (watts) and relative (W/kg) power outputs were significantly better on the carbohydrate restricted diet (p = 0.03 and 0.02 respectively). Both sexes responded similarly in terms of performance whilst only women significantly improved body composition when carbohydrate was restricted (p = 0.02). Results from this study highlight that when carbohydrate is restricted during training, trained endurance athletes do not suffer a reduction in ultra-endurance performance.
... Assim, estudos mostram maiores concentrações circulantes de ácidos graxos livres e de glicerol, um marcador da lipólise (GREENHAFF et al., 1988;WEBSTER et al., 2016;BURKE et al., 2017). Yeo et al. (2011), enfatizam a importância do treinamento na eficiência muscular esquelética para captar, transportar e oxidar ácidos graxos, associado à biogênese mitocondrial, pois reduz a dependência muscular da utilização de glicose como substrato energético durante o exercício prolongado. ...
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Universities are living repositories of the heritage of humanity. They are constantly renewed because they are used differently by society, mostly professors, students and researchers. The University is multidisciplinary pushing each individual to overcome the limits of their cultural and scientific environment, expanding a holistic view of the world. In this context professors and trainees of the Biological Collection of the Southern Amazon (ABAM), from the Federal University of Mato Grosso, câmpus of Sinop, with the support of the Center for Biodiversity Studies of the Amazon Mato-Grossense (NEBAM), created in 2012, the ongoing extension project “Itinerant Museum of Flora and Fauna of the Amazon Mato-Grossense”. The Itinerant Museum which aims, through extension actions, to promote environmental education for children, teenagers and adults, promoting their interest and curiosity on the natural environment and the its enormous biodiversity. The project's activities consist of broad interaction between the university and society, as both visitors enter the university in search of knowledge as the Museum travels to daycare centers, schools and other institutions. We believe that proposals like this will make us capable to overcome the challenges setting science and society apart. During the Museum's visits, our team of undergraduate and graduate students and professors exhibit the biological material forms our collections and explains the subjects, opening to visitors for questions and comments. Then, the participants have access to the materials (living, dry and/or taxidermized organisms) the small material samples may be also examined in a stereomicroscope, always with the help of a supervisor. The engagement and reach magnitude of the projects is enormous and, now, besides the visits to UFMT, the Museum is serving other municipalities in the region, expanding its range of operations and reaching even more people, creating conscience in society on the importance of biodiversity conservation for human life. More than 40 schools have already participated in the actions, comprising more than 13,000 children, teenagers and adults. Among our results are also UFMT institutional stand out, expanding and consolidating connections with society and students, additionally contributing to regional development and disseminating knowledge to the general public. The use of different learning strategies, including the approach and contact of children and young people with regional biodiversity, is central in growing critical and active citizens, protagonists of future actions in sustainable socioeconomic development. Thus, the university extension activities developed by the project, effectively act in the interaction between the University and the regional community, being, a pioneer work in the city.
... It affects physical health and has positive effects on fat oxidation but shows conflicting results regarding the effects of a KD on performance, which are mostly shown in the long term. Thus, there are both beneficial and detrimental effects after using a KD strategy in athletic populations [10,[51][52][53]. Further research is required to establish recommended protocols regarding a KD for athletes. ...
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Evidence shows that the use of food strategies can impact health, but a clear consensus about how the effects of different food strategies impact improvement in the athlete's performance and health remain unclear. This study evaluated how food strategies, specifically intermittent fasting and a ketogenic diet affect health and performance in healthy athletes. Study selection for this review was based on clinical trial studies analyzing changes in performance and health in athletes. The Pubmed, Web of Science, PEDro, Dialnet, Scopus, CINAHL, ProQuest, Medline and Cochrane databases were searched. The Physiotherapy Evidence Database (PEDro) scale, PEDro Internal Validity Scale (IVS) and Standard Quality Assessment Criteria for Evaluating Primary Research Papers from a variety of fields (QUALSYT) checklists were used to evaluate the risk of bias of the included studies. Articles were selected based on criteria concerning the effectiveness of nutritional strategies on athletes' performance; articles should be randomized clinical trials (RCTs) or uncontrolled clinical trials; they should be human studies and they should have been published less than 7 years ago. A total of 15 articles were evaluated, 8 randomised clinical trials and 7 non-randomized clinical studies, with 411 participants who satisfied our inclusion criteria and were included in this review. The results of the study showed intermittent fasting and time-restricted feeding as strategies that produce health benefits. On the other hand, the ketogenic diet did not reach an appropriate consensus. The articles presented a medium level of methodological quality in the PEDro scale, low quality in IVS scale and high quality in QUALSYT scale. Despite the lack of studies analyzing changes in the performance and health of athletes after the use of different nutritional strategies, intermittent fasting and time-restricted feeding should be considered since they seem to be effective, and further studies are necessary.
... It is well-known that the macronutrient content of the diet influences substrate oxidation during exercise. [37][38][39] In the present study, the absolute (g/day) content of dietary fat and protein decreased during the intervention, while dietary carbohydrate remained at a high constant amount, namely, an average of 929 ± 31 and 848 ± 46 g/day for younger and older participants, respectively (Table S2), corresponding to ~12 g/kg BW/day (Table S2). It is very likely that this massive intake of dietary carbohydrate had a significant impact on substrate oxidation in study participants during the intervention. ...
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Aim & methods: Extreme endurance exercise provides a valuable research model for understanding the adaptive metabolic response of older and younger individuals to intense physical activity. Here, we compare a wide range of metabolic and physiologic parameters in two cohorts of seven trained men, age 30±5 years or age 65±6 years, before and after the participants travelled ≈3000 km by bicycle over 15 days. Results: Over the 15-day exercise intervention, participants lost 2-3 kg fat mass with no significant change in body weight. V̇O2 max did not change in younger cyclists, but decreased (p=0.06) in the older cohort. The resting plasma FFA concentration decreased markedly in both groups, and plasma glucose increased in the younger group. In the older cohort, plasma LDL-cholesterol and plasma triglyceride decreased. In skeletal muscle, fat transporters CD36 and FABPm remained unchanged. The glucose handling proteins GLUT4 and SNAP23 increased in both groups. Mitochondrial ROS production decreased in both groups and ADP sensitivity increased in skeletal muscle in the older but not in the younger cohort. Conclusion: In summary, these data suggest that older but not younger individuals experience a negative adaptive response affecting cardiovascular function in response to extreme endurance exercise, while a positive response to the same exercise intervention is observed in peripheral tissues in younger and older men. The results also suggest that the adaptive thresholds differ in younger and old men, and this difference primarily affects central cardiovascular functions in older men after extreme endurance exercise.
... Moreover, previous reviews have only briefly covered the topics of T, cortisol, and LC diets; with none including meta-analyses or statistical investigations of heterogeneity (Kang et al., 2020). Of particular interest is the duration of LC diets, as these diets have an adaptation period of ∼3 weeks (Burke et al., 2017), or longer (Sherrier and Li, 2019). Thus, the effects on steroid hormones may differ pre-and post-adaptation. ...
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Background: Low-carbohydrate diets may have endocrine effects, although individual studies are conflicting. Therefore, a review was conducted on the effects of low- versus high-carbohydrate diets on men's testosterone and cortisol. Methods: The review was registered on PROSPERO (CRD42021255957). The inclusion criteria were: intervention study, healthy adult males, and low-carbohydrate diet: ≤35% carbohydrate. Eight databases were searched from conception to May 2021. Cochrane's risk of bias tool was used for quality assessment. Random-effects, meta-analyses using standardized mean differences and 95% confidence intervals, were performed with Review Manager. Subgroup analyses were conducted for diet duration, protein intake, and exercise duration. Results: Twenty-seven studies were included, with a total of 309 participants. Short-term (<3 weeks), low- versus high-carbohydrate diets moderately increased resting cortisol (0.41 [0.16, 0.66], p < 0.01). Whereas, long-term (≥3 weeks), low-carbohydrate diets had no consistent effect on resting cortisol. Low- versus high-carbohydrate diets resulted in much higher post-exercise cortisol, after long-duration exercise (≥20 min): 0 h (0.78 [0.47, 1.1], p < 0.01), 1 h (0.81 [0.31, 1.31], p < 0.01), and 2 h (0.82 [0.33, 1.3], p < 0.01). Moderate-protein (<35%), low-carbohydrate diets had no consistent effect on resting total testosterone, however high-protein (≥35%), low-carbohydrate diets greatly decreased resting (−1.08 [−1.67, −0.48], p < 0.01) and post-exercise total testosterone (−1.01 [−2, −0.01] p = 0.05). Conclusions: Resting and post-exercise cortisol increase during the first 3 weeks of a low-carbohydrate diet. Afterwards, resting cortisol appears to return to baseline, whilst post-exercise cortisol remains elevated. High-protein diets cause a large decrease in resting total testosterone (∼5.23 nmol/L).
... In Japan, the composition of meals has changed over time because of the westernization of food (14). In addition, athletes can choose special diets to make their training more effective and to achieve their ideal body composition or weight for each competition (15), for example a high-fat diet (16,17), and a high-carbohydrate diet (18). For some athletes, especially long-distance runners, their diet is important because their physical condition or body mass can affect their performance. ...
Article
The food quotient (FQ), which is the rate of macronutrient composition calculated from daily meals, can equal the respiratory quotient over a long term. The FQ is needed to estimate the total energy expenditure (TEE) in doubly labeled water studies. Usually, dietary records (DR) are used for dietary assessment in clinical nutritional studies; however, the DR method's disadvantage is that it takes time to calculate the results. In comparison, the food frequency questionnaires (FFQ) method is a simple and quick way to calculate results. This study aimed to assess the FQ in Japanese runners, and to compare the two dietary assessment methods, DR and FFQ, to examine whether FFQ is useful in calculating the FQ in healthy young adults and runner. The study consisted of 27 runners and 22 healthy young adults. The participants recorded and took pictures all their meals for 1 wk and provided the FFQ for the same week. The FQ was calculated using the proportions of proteins, fats, carbohydrates, and alcohol. There were no significant differences between the FQs of the runners 0.867 (male: 0.873, female: 0.863) and the healthy young adults 0.871 (male: 0.875, female: 0.867) according to the DR methods. There were no differences in the FQs between DR and FFQ methods for all groups. A significant correlation between the FQs (r=0.502, p<0.01), estimated using the DR, and the FQs estimated using the FFQ was observed. These results suggest that use of the FFQ method can provide comparable data for runners and healthy young adults.
... This is elegantly demonstrated by the nonsignificant differences in V _ O 2max in a group of U23 professional cyclists (9) despite differences in their level of performance. Third, reported V _ O 2max in Olympians, professional athletes, and world record holders would have them classified into inferior categories based purely on V _ O 2max (8,10,11). Finally, there can be large discrepancies in V _ O 2max between athletes with similar performance capabilities, for example, V _ O 2max in world-class marathon runners can differ by up to 22 mL·kg À1 ·min À1 (10). ...
... The high concentration of carbohydrates, and type of carbohydrate, found in a PB diet may offer performance advantages through assisting athletes in meeting carbohydrate recommendations for their activity levels, ensuring optimal glycogen concentrations, and preventing early fatigue (Barnard et al. 2019). Burke et al. (2017) observed not only improved race performance in trained race walkers but also improved exercise economy at a given pace in those consuming chronic high carbohydrate diets compared to those consuming a low high fat, low carbohydrate (i.e., "keto") diet. As such, the International Society for Sport Nutrition recommends athletes engaging in "moderate amounts of intense exercise" should consume 5-8 g/kg body weight carbohydrate daily to maintain liver and muscle glycogen (Kerksick et al. 2018). ...
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Individuals may opt to follow a plant-based diet for a variety of reasons, such as religious practices, health benefits or concerns for animal or environmental welfare. Such diets offer a broad spectrum of health benefits including aiding in the prevention and management of chronic diseases. In addition to health benefits, a plant-based diet may provide performance-enhancing effects for various types of exercise due to high carbohydrate levels and the high concentration of antioxidants and phytochemicals found in a plant-based diet. However, some plant-based foods also contain anti-nutrional factors, such as phytate and tannins, which decrease the bioavailability of key nutrients, such as iron, zinc, and protein. Thus, plant-based diets must be carefully planned to ensure adequate intake and absorption of energy and all essential nutrients. The current narrative review summarizes the current state of the research concerning the implications of a plant-based diet for health and exercise performance. It also outlines strategies to enhance the bioavailability of nutrients, sources of hard-to-get nutrients, and sport supplements that could interest plant-based athletes.
... The findings indicated most coaches, athletic trainers, and conditioning specialists stated registered dietitians were their nutrition resources. Burke et al. (2017) concluded a significant increase in fat oxidation capacity during intense exercise. Also, the article had mentioned chronic adaptation to a ketogenic low-carbohydrate, high-fat diet impairs the exercise economy. ...
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A well-balanced diet is essential for individuals, particularly athletes, because it improves overall health by supplying energy besides repairing and replacing damaged cells. A well-balanced diet is also benefitting athletes to fuel their bodies before, during, and after training. This study aims to examine the intellectual structure of sports nutrition research using bibliometric measures from 1959 to 2021 based on the Scopus database. The study was investigated using SciMAT software, which employed keyword co-occurrence analysis to extract performance and scientific output vis-à-vis critical topics or themes in sports nutrition. The findings indicated that sports nutrition possesses enormous potential and growth potential. The most prevalent themes in this research area are trace elements, exercise, questionnaire, carbohydrate, and adolescent. Also, this study put up to analysing sports nutrition in countless fields, assisting in understanding its intellectual structure. Future researchers could use this data to identify the focus of awareness and make decisions in multiple ways. This study has a few limitations: 1) the researchers’ interpretation of the themes in this study was grounded on their knowledge; 2) this study only considered publication records from the Scopus database, and some sports nutrition publications may not have been included; and 3) if additional databases, such as Google Scholar, Microsoft Academics, or Dimensions, were accessed, the subject area may have shifted. The findings of this study should be accepted as a single evidence-based framework for developing future studies on sports nutrition research that will benefit researchers, practitioners, and policymakers.
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Ketogenic diets and orally administered exogenous ketone supplements are strategies to increase serum ketone bodies serving as an alternative energy fuel for high energy demanding tissues, such as the brain, muscles, and the heart. The ketogenic diet is a low-carbohydrate and fat-rich diet, whereas ketone supplements are usually supplied as esters or salts. Nutritional ketosis, defined as serum ketone concentrations of ≥ 0.5 mmol/L, has a fasting-like effect and results in all sorts of metabolic shifts and thereby enhancing the health status. In this review, we thus discuss the different interventions to reach nutritional ketosis, and summarize the effects on heart diseases, epilepsy, mitochondrial diseases, and neurodegenerative disorders. Interest in the proposed therapeutic benefits of nutritional ketosis has been growing the past recent years. The implication of this nutritional intervention is becoming more evident and has shown interesting potential. Mechanistic insights explaining the overall health effects of the ketogenic state, will lead to precision nutrition for the latter diseases.
Article
Omega-3 polyunsaturated fatty acids (omega-3 PUFAs) are essential for improving the health and performance of athletes. The present study aimed to evaluate the nutritional status of omega-3 PUFAs in Chinese elite athletes by both dietary intake analysis and serum biomarker detection. A cross-sectional analysis of data from 54 elite athletes (24 men and 30 women) from Shanghai professional sports teams was conducted. A food frequency questionnaire (FFQ) was employed to analyze dietary intake, and gas chromatography-mass spectrometry (GC-MS/MS) was conducted to measure serum biomarkers of PUFAs. Correlation analysis was performed to investigate the relationships of PUFA biomarkers with diet, inflammation and oxidative stress. The results showed that the median intake of EPA + DHA among athletes was 132 mg/d, which is lower than the minimum value recommended by dietary guidelines (250 mg/d). The average serum EPA + DHA was 4.0 ± 1.1%, and the ratio of omega-6/omega-3 was 7.7 ± 1.7. Most (96.3%) of the athletes were below the targeted value of serum EPA + DHA, which is associated with a reduction in cardiovascular risk. Correlation analysis showed that the serum EPA + DHA was positively correlated with the long-term dietary intake of EPA + DHA and negatively correlated with inflammatory markers. In conclusion, the serum circulating EPA + DHA and omega-6/omega-3 ratio are effective biomarkers reflecting the nutritional status of PUFAs in athletes. Omega-3 PUFAs have a potential effect on inhibiting inflammatory markers. Hence, it is necessary for Chinese athletes to improve their suboptimal nutritional status of PUFAs through dietary intervention.
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Iwayama, K, Tanabe, Y, Yajima, K, Tanji, F, Onishi, T, and Takahashi, H. Preexercise high-fat meal following carbohydrate loading attenuates glycogen utilization during endurance exercise in male recreational runners. J Strength Cond Res XX(X): 000-000, 2022-This study aimed to investigate whether one preexercise high-fat meal can increase glycogen conservation during endurance exercise, as compared with one preexercise high-carbohydrate meal. Ten young male recreational runners (22.0 ± 0.6 years; 171.3 ± 0.9 cm; 58.3 ± 1.9 kg; maximal oxygen uptake [V̇o2max], 62.0 ± 1.6 ml·kg-1·min-1) completed 2 exercise trials after high-carbohydrate loading: eating a high-carbohydrate (CHO; 7% protein, 13% fat, 80% carbohydrate) meal or eating a high-fat (FAT; 7% protein, 42% fat, 52% carbohydrate) meal 3.5 hours before exercise. The order of the 2 trials was randomized, and the interval between trials was at least 1 week. The experimental exercise consisted of running on a treadmill for 60 minutes at 95% of each subject's lactate threshold. Muscle and liver glycogen content were assessed using noninvasive carbon magnetic resonance spectroscopy before the experimental meal as well as before and after exercise; respiratory gases were measured continuously during exercise. The respiratory exchange ratio during exercise was statistically lower in the FAT trial than in the CHO trial (p < 0.01). In addition, muscle (p < 0.05) and liver (p < 0.05) glycogen utilization during exercise was less in the FAT trial than in the CHO trial. Therefore, one high-fat meal following carbohydrate loading reduced muscle and liver glycogen use during the 60-minute exercise. These results suggest that this dietary approach may be applied as a strategy to optimize energy utilization during endurance exercise.
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A major goal of training to improve the performance of prolonged, continuous, endurance events lasting up to 3 h is to promote a range of physiological and metabolic adaptations that permit an athlete to work at both higher absolute and relative power outputs/speeds and delay the onset of fatigue (i.e., a decline in exercise intensity). To meet these goals, competitive endurance athletes undertake a prodigious volume of training, with a large proportion performed at intensities that are close to or faster than race pace and highly dependent on carbohydrate (CHO)-based fuels to sustain rates of muscle energy production [i.e., match rates of adenosine triphosphate (ATP) hydrolysis with rates of resynthesis]. Consequently, to sustain muscle energy reserves and meet the daily demands of training sessions, competitive athletes freely select CHO-rich diets. Despite renewed interest in high-fat, low-CHO diets for endurance sport, fat-rich diets do not improve training capacity or performance, but directly impair rates of muscle glycogenolysis and energy flux, limiting high-intensity ATP production. When highly trained athletes compete in endurance events lasting up to 3 h, CHO-, not fat-based fuels are the predominant fuel for the working muscles and CHO, not fat, availability becomes rate limiting for performance.
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During the period 1985-2005, studies examined the proposal that adaptation to a low-carbohydrate (<25 % energy), high-fat (>60 % energy) diet (LCHF) to increase muscle fat utilization during exercise could enhance performance in trained individuals by reducing reliance on muscle glycogen. As little as 5 days of training with LCHF retools the muscle to enhance fat-burning capacity with robust changes that persist despite acute strategies to restore carbohydrate availability (e.g., glycogen supercompensation, carbohydrate intake during exercise). Furthermore, a 2- to 3-week exposure to minimal carbohydrate (<20 g/day) intake achieves adaptation to high blood ketone concentrations. However, the failure to detect clear performance benefits during endurance/ultra-endurance protocols, combined with evidence of impaired performance of high-intensity exercise via a down-regulation of carbohydrate metabolism led this author to dismiss the use of such fat-adaptation strategies by competitive athletes in conventional sports. Recent re-emergence of interest in LCHF diets, coupled with anecdotes of improved performance by sportspeople who follow them, has created a need to re-examine the potential benefits of this eating style. Unfortunately, the absence of new data prevents a different conclusion from being made. Notwithstanding the outcomes of future research, there is a need for better recognition of current sports nutrition guidelines that promote an individualized and periodized approach to fuel availability during training, allowing the athlete to prepare for competition performance with metabolic flexibility and optimal utilization of all muscle substrates. Nevertheless, there may be a few scenarios where LCHF diets are of benefit, or at least are not detrimental, for sports performance.
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We determined the effects of 'periodized nutrition' on skeletal muscle and whole-body responses to a bout of prolonged exercise the following morning. Seven cyclists completed two trials receiving isoenergetic diets differing in the timing of ingestion: They consumed either 8 g•kg(-1) BM of CHO before undertaking an evening session of high-intensity training (HIT) and slept without eating (FASTED), or 4 g•kg(-1) BM of CHO before HIT then 4 g•kg(-1) BM of CHO before sleeping (FED). The next morning subjects completed 2 h cycling (120SS) while overnight fasted. Muscle biopsies were taken on day 1 (D1) before and 2 h after HIT and on Day 2 (D2) pre-, post-, and 4 h after 120SS. Muscle [glycogen] was higher in FED at all times post-HIT (P< 0.001). HIT increased PGC1α mRNA (P< 0.01) while PDK4 mRNA was elevated to a greater extent in FASTED (P< 0.05). Resting phosphorylation of AMPK(Thr172), p38MAPK(Thr180/Tyr182) and p-ACC(Ser79) (D2) was greater in FASTED (P< 0.05). Fat oxidation during 120SS was higher in FASTED (P< 0.01) coinciding with increases in ACC(Ser79) and CPT1, as well as mRNA expression of CD36 and FABP3 (P< 0.05). Methylation on the gene promoter for COX4I1 and FABP3 increased 4 h after 120SS in both trials, while methylation of the PPARδ promoter increased only in FASTED. We provide evidence for shifts in DNA methylation that correspond with inverse changes in transcription for metabolically adaptive genes, although delaying post-exercise feeding failed to augment markers of mitochondrial biogenesis. Copyright © 2014, Journal of Applied Physiology.
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Abstract A key element contributing to deteriorating exercise capacity during physically demanding sport appears to be reduced carbohydrate availability coupled with an inability to effectively utilize alternative lipid fuel sources. Paradoxically, cognitive and physical decline associated with glycogen depletion occurs in the presence of an over-abundance of fuel stored as body fat that the athlete is apparently unable to access effectively. Current fuelling tactics that emphasize high-carbohydrate intakes before and during exercise inhibit fat utilization. The most efficient approach to accelerate the body's ability to oxidize fat is to lower dietary carbohydrate intake to a level that results in nutritional ketosis (i.e., circulating ketone levels >0.5 mmol/L) while increasing fat intake for a period of several weeks. The coordinated set of metabolic adaptations that ensures proper interorgan fuel supply in the face of low-carbohydrate availability is referred to as keto-adaptation. Beyond simply providing a stable source of fuel for the brain, the major circulating ketone body, beta-hydroxybutyrate, has recently been shown to act as a signalling molecule capable of altering gene expression, eliciting complementary effects of keto-adaptation that could extend human physical and mental performance beyond current expectation. In this paper, we review these new findings and propose that the shift to fatty acids and ketones as primary fuels when dietary carbohydrate is restricted could be of benefit for some athletes.
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Purpose To determine the effect of intravenous iron supplementation on performance, fatigue and overall mood in runners without clinical iron deficiency. Methods Fourteen distance runners with serum ferritin 30–100 µg·L−1 were randomly assigned to receive three blinded injections of intravenous ferric-carboxymaltose (2 ml, 100 mg, IRON) or normal saline (PLACEBO) over four weeks (weeks 0, 2, 4). Athletes performed a 3,000 m time trial and 10×400 m monitored training session on consecutive days at week 0 and again following each injection. Hemoglobin mass (Hbmass) was assessed via carbon monoxide rebreathing at weeks 0 and 6. Fatigue and mood were determined bi-weekly until week 6 via Total Fatigue Score (TFS) and Total Mood Disturbance (TMD) using the Brief Fatigue Inventory and Brunel Mood Scale. Data were analyzed using magnitude-based inferences, based on the unequal variances t-statistic and Cohen's Effect sizes (ES). Results Serum ferritin increased in IRON only (Week 0: 62.8±21.9, Week 4: 128.1±46.6 µg·L−1; p = 0.002) and remained elevated two weeks after the final injection (127.0±66.3 µg·L−1, p = 0.01), without significant changes in Hbmass. Supplementation had a moderate effect on TMD of IRON (ES -0.77) with scores at week 6 lower than PLACEBO (ES -1.58, p = 0.02). Similarly, at week 6, TFS was significantly improved in IRON vs. PLACEBO (ES –1.54, p = 0.05). There were no significant improvements in 3,000 m time in either group (Week 0 vs. Week 4; Iron: 625.6±55.5 s vs. 625.4±52.7 s; PLACEBO: 624.8±47.2 s vs. 639.1±59.7 s); but IRON reduced their average time for the 10×400 m training session at week 2 (Week 0: 78.0±6.6 s, Week 2: 77.2±6.3; ES–0.20, p = 0.004). Conclusion During 6 weeks of training, intravenous iron supplementation improved perceived fatigue and mood of trained athletes with no clinical iron deficiency, without concurrent improvements in oxygen transport capacity or performance.
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