Article

Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise

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Abstract

This study determined if the suppression of lipolysis after preexercise carbohydrate ingestion reduces fat oxidation during exercise. Six healthy, active men cycled 60 min at 44 +/- 2% peak oxygen consumption, exactly 1 h after ingesting 0.8 g/kg of glucose (Glc) or fructose (Fru) or after an overnight fast (Fast). The mean plasma insulin concentration during the 50 min before exercise was different among Fast, Fru, and Glc (8 +/- 1, 17 +/- 1, and 38 +/- 5 microU/ml, respectively; P < 0.05). After 25 min of exercise, whole body lipolysis was 6.9 +/- 0.2, 4.3 +/- 0.3, and 3.2 +/- 0.5 micromol x kg(-1) x min(-1) and fat oxidation was 6.1 +/- 0.2, 4.2 +/- 0.5, and 3.1 +/- 0.3 micromol x kg(-1) x min(-1) during Fast, Fru, and Glc, respectively (all P < 0.05). During Fast, fat oxidation was less than lipolysis (P < 0.05), whereas fat oxidation approximately equaled lipolysis during Fru and Glc. In an additional trial, the same subjects ingested glucose (0.8 g/kg) 1 h before exercise and lipolysis was simultaneously increased by infusing Intralipid and heparin throughout the resting and exercise periods (Glc+Lipid). This elevation of lipolysis during Glc+Lipid increased fat oxidation 30% above Glc (4.0 +/- 0.4 vs. 3.1 +/- 0.3 micromol x kg(-1) x min(-1); P < 0.05), confirming that lipolysis limited fat oxidation. In summary, small elevations in plasma insulin before exercise suppressed lipolysis during exercise to the point at which it equaled and appeared to limit fat oxidation.

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... Indeed, CHO ingestion during exercise appears to suppress or even abolish hepatic glucose output during exercise, thus attenuating the decline in liver glycogen content [53]. In relation to lipid metabolism, CHO feeding attenuates lipolysis in adipose tissue (as mediated via anti-lipolytic effects of insulin) such that plasma FFA availability is reduced during exercise undertaken in CHO fed conditions [54]. Horowitz et al. [54] studied male participants during 60 min of exercise at 45% VO 2max in fasted conditions, or 1 h after consuming 0.8 g·kg −1 of glucose (to induce a high insulin response) or 0.8 g·kg −1 fructose (to induce a low insulin response), or in an additional glucose trial during which intralipid and heparin were infused so as to maintain plasma FFA availability in the face of high insulin. ...
... In relation to lipid metabolism, CHO feeding attenuates lipolysis in adipose tissue (as mediated via anti-lipolytic effects of insulin) such that plasma FFA availability is reduced during exercise undertaken in CHO fed conditions [54]. Horowitz et al. [54] studied male participants during 60 min of exercise at 45% VO 2max in fasted conditions, or 1 h after consuming 0.8 g·kg −1 of glucose (to induce a high insulin response) or 0.8 g·kg −1 fructose (to induce a low insulin response), or in an additional glucose trial during which intralipid and heparin were infused so as to maintain plasma FFA availability in the face of high insulin. In accordance with the insulin response in CHO fed conditions, lipolysis (as indicated by rate of appearance of glycerol), FFA availability and lipid oxidation were reduced. ...
... Performing endurance training in the fasted state represents a simpler model of "training low" where exercise is performed prior to breakfast. Although pre-exercise muscle glycogen is not altered as a result of the overnight fast, liver glycogen remains lower whilst FFA availability is increased [54] compared with when breakfast is fed. Exercising in the fasted state increases post-exercise AMPK activity [101] and mRNA of genes controlling substrate utilization (PDK4, GLUT4, CD36, CPT-1) and mitochondrial function (UCP3) [102,103] compared with when CHO is fed before and during exercise. ...
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Since the introduction of the muscle biopsy technique in the late 1960s, our understanding of the regulation of muscle glycogen storage and metabolism has advanced considerably. Muscle glycogenolysis and rates of carbohydrate (CHO) oxidation are affected by factors such as exercise intensity, duration, training status and substrate availability. Such changes to the global exercise stimulus exert regulatory effects on key enzymes and transport proteins via both hormonal control and local allosteric regulation. Given the well-documented effects of high CHO availability on promoting exercise performance, elite endurance athletes are typically advised to ensure high CHO availability before, during and after high-intensity training sessions or competition. Nonetheless, in recognition that the glycogen granule is more than a simple fuel store, it is now also accepted that glycogen is a potent regulator of the molecular cell signaling pathways that regulate the oxidative phenotype. Accordingly, the concept of deliberately training with low CHO availability has now gained increased popularity amongst athletic circles. In this review, we present an overview of the regulatory control of CHO metabolism during exercise (with a specific emphasis on muscle glycogen utilization) in order to discuss the effects of both high and low CHO availability on modulating exercise performance and training adaptations, respectively.
... However, data are conflicting with regard to which hormone predominates with preexercise carbohydrate ingestion and the ultimate effect on lipolysis. Horowitz et al. (9) reported attenuated whole-body lipolysis during cycling (44% maximal oxygen consumption (V O 2max )) after 0.8 gIkg j1 glucose or fructose consumed 1 h before exercise. In contrast, a similar study (121, 20, and 31 g for carbohydrate, fat, and protein, respectively; 1 h before cycling at 55% V O 2max ) reported no differences in adipose tissue lipolysis but did find evidence for enhanced FFA reesterification after meal ingestion (10). ...
... Specifically, at a power (1 j A) of 0.80 and an > level of 0.05, a sample size of 11 was required. Although our final sample size of 10 was slightly underpowered (1 j A = 0.77), this sample size is in line with similar studies and provides reasonable power (9,10,27). ...
... Prior studies examining the effect of preexercise carbohydrate on resting and exercise adipose tissue lipolysis are conflicting. Using stable isotopes, Horowitz et al. (9) reported attenuated whole-body lipolysis at rest and during exercise (44% V O 2max cycling) with ingestion of either glucose or fructose (0.8 gIkg j1 ) versus a placebo 60 min before exercise. In a similarly designed study but using arteriovenous difference methods, Enevoldsen et al. (10) reported reduced adipose tissue lipolysis at rest, but no change during exercise (55% V O 2max cycling) with ingestion of a high-carbohydrate meal (121 T 8 g carbohydrate, 20 T 1 g fat, and 21 T 3 g protein) 60 min before exercise compared with fasting. ...
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Purpose: To determine the impact of pre-exercise carbohydrate of different glycemic indices on subcutaneous abdominal adipose tissue (SCAAT) metabolism and running performance. Methods: Ten trained male runners completed three experimental trials consisting of 30 min at 60% VO2max, 30 min at 75% VO2max, and a 5-km time trial (TT). Thirty min prior to exercise, participants consumed one of three beverages: 1) 75 g low glycemic index modified starch supplement (UCAN), 2) 75 g high glycemic index glucose-based supplement (G), or 3) a flavor-matched non-caloric placebo (PL). SCAAT lipolysis was assessed via microdialysis. Results: Prior to exercise, blood glucose and insulin were elevated with G vs. PL (+53.0 ± 21.3 mg[BULLET OPERATOR]dL [SD]; p < 0.0001; +33.9 ± 11.0 μU[BULLET OPERATOR]mL; p < 0.0001) and G vs. UCAN (+36.6 ± 24.9 mg[BULLET OPERATOR]dL; p < 0.0001; +25.2 ± 11.0 μU[BULLET OPERATOR]mL; p < 0.0001), respectively. Fat oxidation was attenuated, and carbohydrate oxidation increased prior to exercise with G vs. PL (-0.06 ± 0.06 g[BULLET OPERATOR]min; p = 0.005; +0.18 ± 0.07 g[BULLET OPERATOR]min; p < 0.0001) and G vs. UCAN (-0.06 ± 0.05 g[BULLET OPERATOR]min; p = 0.004; +0.18 ± 0.14 g[BULLET OPERATOR]min; p < 0.0001). However, there were no differences in SCAAT lipolysis at rest or during running at either exercise intensity. Also, there was no effect of treatment on running performance. Conclusions: Pre-exercise carbohydrate lowers fat oxidation and increases carbohydrate oxidation, and these effects are attenuated with low glycemic index carbohydrate. However, these changes are not the result of alterations in SCAAT lipolysis, nor do they affect running performance.
... Stocks et al. [162] found that undertaking moderate-to high-intensity steady-state exercise (70% W max ) in the fasted state increased fatty acid availability, augmented AMPK Thr172 phosphorylation and increased PDK4 mRNA expression compared to the same exercise bout in the fed state. Carbohydrate intake before and during exercise stimulates a contribution of blood glucose to the metabolic substrate pool fuelling muscle and inhibits fat oxidation due to higher glycolytic flux and pyruvate oxidation by the pyruvate dehydrogenase complex [167][168][169][170][171][172]. This leads to attenuated lipid utilisation during exercise [10,168], mainly via higher insulin concentrations, which inhibits lipolysis both of the adipose tissues stores (reducing plasma NEFA concentrations) and the IMTG stores [173,174]. ...
... Carbohydrate intake before and during exercise stimulates a contribution of blood glucose to the metabolic substrate pool fuelling muscle and inhibits fat oxidation due to higher glycolytic flux and pyruvate oxidation by the pyruvate dehydrogenase complex [167][168][169][170][171][172]. This leads to attenuated lipid utilisation during exercise [10,168], mainly via higher insulin concentrations, which inhibits lipolysis both of the adipose tissues stores (reducing plasma NEFA concentrations) and the IMTG stores [173,174]. The high insulin concentration, as typically occurs in the post meal state particularly if carbohydrates are consumed, will also suppress liver glycogen breakdown and gluconeogenesis, meaning that glucose production by the liver will not match glucose oxidation by the muscle, so blood glucose concentration will fall [175]. ...
Article
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Around 80% of individuals with Type 1 diabetes (T1D) in the United States do not achieve glycaemic targets and the prevalence of comorbidities suggests that novel therapeutic strategies, including lifestyle modification, are needed. Current nutrition guidelines suggest a flexible approach to carbohydrate intake matched with intensive insulin therapy. These guidelines are designed to facilitate greater freedom around nutritional choices but they may lead to higher caloric intakes and potentially unhealthy eating patterns that are contributing to the high prevalence of obesity and metabolic syndrome in people with T1D. Low carbohydrate diets (LCD; <130 g/day) may represent a means to improve glycaemic control and metabolic health in people with T1D. Regular recreational exercise or achieving a high level of athletic performance is important for many living with T1D. Research conducted on people without T1D suggests that training with reduced carbohydrate availability (often termed “train low”) enhances metabolic adaptation compared to training with normal or high carbohydrate availability. However, these “train low” practices have not been tested in athletes with T1D. This review aims to investigate the known pros and cons of LCDs as a potentially effective, achievable, and safe therapy to improve glycaemic control and metabolic health in people with T1D. Secondly, we discuss the potential for low, restricted, or periodised carbohydrate diets in athletes with T1D.
... One method of achieving this is through manipulation of the pre-exercise meal. It has been well established that ingesting a carbohydrate-rich meal prior to low-intensity endurance exercise decreases fat oxidation during exercise Horowitz et al. 1997;Jeukendrup 2003;Spriet 2014;Vieira et al. 2016). However, there is a lack of research on how feeding before exercise affects postexercise metabolism, and of the evidence that does exist the results are inconclusive. ...
... Fat oxidation was elevated by >60% compared with rest during the postexercise period, which is in line with previous research regarding fat oxidation and SIT (Burns et al. 2012;Chan and Burns 2013;Islam et al. 2017a;Williams et al. 2013). Although research shows that exercising in the fasted state leads to greater fat oxi-dation during endurance exercise than the fed state Horowitz et al. 1997;Jeukendrup 2003;Spriet 2014;Vieira et al. 2016), it is not possible to measure fat oxidation during or immediately after SIT with gas exchange because of hyperventilation and increased V CO 2 ). Additionally, research has shown that at exercise intensities above 60% V O 2max there are no differences in fat oxidation between exercise performed in the fed or fasted state (Bergman and Brooks 1999;Vieira et al. 2016). ...
Article
Sprint interval training (SIT) has demonstrated reductions in fat mass through potential alterations in postexercise metabolism. This study examined whether exercising in the fasted or fed state affects postexercise metabolism following acute SIT. Ten active males performed a bout of modified SIT (8 × 15-s sprints; 120 s recovery) in both a fasted (FAST) and fed (FED) state. Gas exchange was collected through 3 h postexercise, appetite perceptions were measured using a visual analog scale, and energy intake was recorded using dietary food logs. There was no difference in energy expenditure between conditions at any time point (p > 0.329) or in total session energy expenditure (FED: 514.8 ± 54.9 kcal, FAST: 504.0 ± 74.3 kcal; p = 0.982). Fat oxidation at 3 h after exercise was higher in FED (0.110 ± 0.04 g·min ⁻¹ ) versus FAST (0.069 ± 0.02 g·min ⁻¹ ; p = 0.013) though not different between conditions across time (p > 0.340) or in total postexercise fat oxidation (FED: 0.125 ± 0.04 g·min ⁻¹ , FAST: 0.105 ± 0.02 g·min ⁻¹ ; p = 0.154). Appetite perceptions were lower in FED (–4815.0 ± 4098.7 mm) versus FAST (–707.5 ± 2010.4 mm, p = 0.022); however, energy intake did not differ between conditions (p = 0.429). These results demonstrate the fasted or fed state does not augment postexercise metabolism following acute SIT in a way that would favour fat loss following training. Novelty Energy expenditure was similar between conditions, while fat oxidation was significantly greater in FED at 3 h after exercise. Appetite perceptions were significantly lower in FED; however, energy intake was not different between conditions. Current findings suggest that performing SIT in the fed or fasted state would not affect fat loss following training.
... A causa della natura dello studio, non abbiamo controllato la dieta dei soggetti o il ciclo mestruale; pertanto, non possiamo discutere degli effetti di questi fattori sull'ossidazione del grasso. In alcuni studi, è stato mostrato che l'ingestione di carboidrati entro ore prima dell'esercizio riduce l'ossidazione del grasso 48,49 . Non abbiamo controllato il consumo di cibo, ma abbiamo avvisato i soggetti di non mangiare per ~12 ore prima del test di esercizio. ...
... In some studies, it has been shown that the ingestion of CHO within hours before exercise reduces fat oxidation. 48,49 We did not control food intake, but cautioned the subjects not to eat ~12 hours before the exercise test. Additionally, the number of the participants included in this study is small, so our results should be confirmed with larger samples. ...
Article
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BACKGROUND: The objective of this study was to investigate the effects of very low volume (in terms of the number of training days and load number in every session) of a high-intensity interval training (HIIT) program on substrate oxidation during incremental exercise until exhaustion in recreationally active women. METHODS: Sixteen young women (N.=8 training; N.=8 controls) voluntarily participated in this study. Before the experiment, peak and mean power outputs were measured by the Wingate Anaerobic Test (WAT), VO2max, the maximal fat oxidation rate (MFO) and Fatmax intensity and were not different between the groups (P>0.05). The training group completed two weeks of HIIT (10 sessions), including 2 WATs in every training session. RESULTS: After the experiment, peak and mean power, VO2max, exhaustion time and CHOpeak increased in the training group. Nevertheless, the MFO and Fatmax intensity values did not change. CONCLUSIONS: These results demonstrated that a 2-week HIIT increased aerobic and anaerobic capacity without any change in the MFO and Fatmax during maximal exercise.
... 11,12 One strategy that has arisen to increase the «burn» fat is to perform a moderate intensity exercise and fasting prior to the session. 13,14 Understood by fasting according to the Royal Spanish Academy as «Abstinence from all food and drink from twelve o'clock antecedent». ...
... 16 However, various investigations have mentioned that fasting raises problems as favoring protein catabolism, decreased sports performance and the risk of hypoglycemia during exercise. 13,14,17,18 Oetinger et al 19 mention that exercise at fasting causes an increase in catecholamines, cortisol and high levels of peptide natriuretrico who plays an important role in exercise-induced lipolysis. In addition, leptin and insulin show a decrease in their concentrations. ...
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Introduction: Young people who start the university life face a key stage for the acquisition of habits and lifestyles. The test Course Navette is one of the most used worldwide because of its easy measurement, validity, effectiveness and sensitivity in different age ranks. Material and methods: An observational, descriptive and transversal study with quantitative approach; with 100 students participating (43 men and 57 women) with an average age of 21.06 ± 2.43 at the University of Santander, Cúcuta. For the development of this research, were obtained measurements anthropometric, hematological, physiological and performance on an empty stomach Leger test. Results: 62% of participants had a BMI of normal weight, 24% overweight and obesity and underweight was 8 and 6% respectively. In turn 32% of men and 17.5% of women have high cardiovascular risk according to abdominal circumference. VO2max. in the Leger test was 32.92 ± 7.12 to 533.80 ± 371.34 meters traveled. Regarding glycemia before the test was 80.99 ± 11.91 and after 105.59 ± 20.89. Conclusion: No significant differences in fat percentage were found (p = 0,863), muscle (p = 0,740) and water (p = 0,804) after Leger test. However, there were significant changes in FC, TAS, TAD, red cells, white cells, hemoglobin, platelets and blood glucose levels (p = 0,000). Regarding the VO2max. (p = 0,597) and travel meters (p = 0,619) no differences were found by gender.
... This effect of CHO ingestion on endurance exercise capacity has been attributed to a retard of the decrease in CHO accumulation during endurance exercise. On the other hand, CHO ingestion promotes CHO oxidation [5], but it inhibits fat oxidation during exercise [6]. Therefore, it is suitable a kind of CHO ingestion that does not strongly promote CHO oxidation and slightly inhibits fat oxidation to increase endurance exercise capacity. ...
... It is generally recognized that CHO ingestion increases CHO oxidation and decreases fat oxidation [5,6]. In the present study, the ISO group showed high levels of fat oxidation compared to the SUC group ( Figure 1A). ...
... In this model, pre-exercise muscle glycogen is not different between fasted or fed conditions, but liver glycogen and circulating glucose is higher during fed conditions. In contrast, increased free fatty acid (FFA) availability and lipid oxidation occur in fasted conditions when exercise is matched for intensity, duration and work performed [25]. Depending on the timing of CHO feeding in relation to the commencement of exercise (e.g.[60 min before exercise versus \10 min before and/or during exercise), such differences in FFA availability may manifest from the beginning of exercise [25] or not until after 30-40 min of exercise, respectively [26]. ...
... In contrast, increased free fatty acid (FFA) availability and lipid oxidation occur in fasted conditions when exercise is matched for intensity, duration and work performed [25]. Depending on the timing of CHO feeding in relation to the commencement of exercise (e.g.[60 min before exercise versus \10 min before and/or during exercise), such differences in FFA availability may manifest from the beginning of exercise [25] or not until after 30-40 min of exercise, respectively [26]. Exercising fasted increases AMP-activated protein kinase (AMPK) activity [27] and post-exercise gene expression [28,29], while several weeks of fasted training increases oxidative enzyme activity [30], lipid transport protein content [31] and resting glycogen storage [32]. ...
Article
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Deliberately training with reduced carbohydrate (CHO) availability to enhance endurance-training-induced metabolic adaptations of skeletal muscle (i.e. the ‘train low, compete high’ paradigm) is a hot topic within sport nutrition. Train-low studies involve periodically training (e.g., 30–50% of training sessions) with reduced CHO availability, where train-low models include twice per day training, fasted training, post-exercise CHO restriction and ‘sleep low, train low’. When compared with high CHO availability, data suggest that augmented cell signalling (73% of 11 studies), gene expression (75% of 12 studies) and training-induced increases in oxidative enzyme activity/protein content (78% of 9 studies) associated with ‘train low’ are especially apparent when training sessions are commenced within a specific range of muscle glycogen concentrations. Nonetheless, such muscle adaptations do not always translate to improved exercise performance (e.g. 37 and 63% of 11 studies show improvements or no change, respectively). Herein, we present our rationale for the glycogen threshold hypothesis, a window of muscle glycogen concentrations that simultaneously permits completion of required training workloads and activation of the molecular machinery regulating training adaptations. We also present the ‘fuel for the work required’ paradigm (representative of an amalgamation of train-low models) whereby CHO availability is adjusted in accordance with the demands of the upcoming training session(s). In order to strategically implement train-low sessions, our challenge now is to quantify the glycogen cost of habitual training sessions (so as to inform the attainment of any potential threshold) and ensure absolute training intensity is not compromised, while also creating a metabolic milieu conducive to facilitating the endurance phenotype.
... In contrast to the findings of the current study, several metabolic chamber studies of Melanson et al. showed no increase in 24-h fat oxidation with increased physical activity, when participants were in energy balance (13,14,32,33) . Because physical activity was performed in the postprandial state, the absence of an increase in 24-h fat oxidation in these studies was explained by an insulinmediated decrease in lipolysis that diminished the supply of FFA (34) . FFA availability in plasma is a major determinant of fat oxidation in muscle during and after physical activity (35) . ...
... Since the magnitude of fat oxidation during physical activity seems to depend on insulin (34) and ...
Article
Body weight control is thought to be improved when physical activity and energy intake are both high (high energy turnover). The aim of this study was to investigate the short-term impact of energy turnover (ET) on fat balance during zero energy balance, caloric restriction and overfeeding. In a randomized crossover study, 9 healthy men (BMI: 23.0 ±2.1 kg/m ² , 26.6 ±3.5 y) passed 3x3 days in a metabolic chamber: 3 levels of ET (low, medium and high; physical activity level = 1.3-1.4, 1.5-1.6 and 1.7-1.8) were performed at zero energy balance (EB), caloric restriction (CR), and overfeeding (OF) (100%, 75%, 125% of individual energy requirement). Different levels of ET were obtained by walking (4 km/h) on a treadmill (0, 165, 330 min). 24-h macronutrient oxidation and relative macronutrient balance (oxidation relative to intake) were calculated and free fatty acids, 24-h insulin and catecholamine secretion were analyzed as determinants of fat oxidation. During EB and OF, 24-h fat oxidation increased with higher ET. This resulted in a higher relative fat balance at medium ET (EB: +17%, OF: +14%) and high ET (EB: +23%, OF: +17%) compared to low ET (all p<0.05). In contrast, CR led to a stimulation of 24-h fat oxidation irrespective of ET (no differences in relative fat balance between ET levels, p>0.05). In conclusion, under highly controlled conditions a higher energy turnover improved relative fat balance in young healthy men during overfeeding and energy balance compared to a sedentary state.
... Weak associations between PFO during fasted incremental cycling and endurance performance in field-based, multisport events have been observed, although between-subject pre-or during-competition controls were not employed (Frandsen et al. 2017;Vest et al. 2019). As fat oxidation is influenced by feeding status Horowitz et al. 1997;Bergman and Brooks 1999), and increases over time during prolonged exercise (Ahlborg et al. 1974;Watt et al. 2002Watt et al. , 2006, PFO measured during fasted, incremental exercise may not reflect metabolic responses to the prolonged, fed-state exercise typically performed in competition. Indeed, relationships between PFO and fat oxidation during prolonged, fed-state exercise are poorly understood. ...
... Routine physiological profiling assessments are commonly conducted after an overnight fast for ease of repetition in follow-up (Maunder et al. 2018b). Given that whole-body fat oxidation rates are greater during exercise in the fasted compared to fed state Horowitz et al. 1997;Bergman and Brooks 1999), and may increase over time during prolonged exercise (Ahlborg et al. 1974;Watt et al. 2002Watt et al. , 2006, whole-body fat oxidation rates during fasted incremental exercise may not be readily transferable to the prolonged fed-state exercise that endurance athletes perform in training and competition. However, the present data suggest PFO measured during fasted incremental cycling can distinguish athletes likely to exhibit higher or lower whole-body fat oxidation rates during prolonged fed-state exercise with CHO feeding (Table 2). ...
Article
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Purpose Whole-body fat oxidation during exercise can be measured non-invasively during athlete profiling. Gaps in understanding exist in the relationships between fat oxidation during incremental fasted exercise and skeletal muscle parameters, endurance performance, and fat oxidation during prolonged fed-state exercise. Methods Seventeen endurance-trained males underwent a (i) fasted, incremental cycling test to assess peak whole-body fat oxidation (PFO), (ii) resting vastus lateralis microbiopsy, and (iii) 30-min maximal-effort cycling time-trial preceded by 2-h of fed-state moderate-intensity cycling to assess endurance performance and fed-state metabolism on separate occasions within one week. Results PFO (0.58 ± 0.28 g.min⁻¹) was associated with vastus lateralis citrate synthase activity (69.2 ± 26.0 μmol.min−1.g⁻¹ muscle protein, r = 0.84, 95% CI 0.58, 0.95, P < 0.001), CD36 abundance (16.8 ± 12.6 μg.g⁻¹ muscle protein, rs = 0.68, 95% CI 0.31, 1.10, P = 0.01), pre-loaded 30-min time-trial performance (251 ± 51 W, r = 0.76, 95% CI 0.40, 0.91, P = 0.001; 3.2 ± 0.6 W.kg⁻¹, r = 0.62, 95% CI 0.16, 0.86, P = 0.01), and fat oxidation during prolonged fed-state cycling (r = 0.83, 95% CI 0.57, 0.94, P < 0.001). Addition of PFO to a traditional model of endurance (peak oxygen uptake, power at 4 mmol.L⁻¹ blood lactate concentration, and gross efficiency) explained an additional ~ 2.6% of variation in 30-min time-trial performance (adjusted R² = 0.903 vs. 0.877). Conclusion These associations suggest non-invasive measures of whole-body fat oxidation during exercise may be useful in the physiological profiling of endurance athletes.
... It is well understood that carbohydrate consumption before exercise leads to an increase in blood glucose levels, and this fuel source (glucose) is efficiently used for muscle contraction, but also inhibits fat oxidation (3,13,14,26,30). Conversely, training in a fasted state has been shown to stimulate the rate of lipolysis and fat oxidation (26,48), partly due to the low levels of insulin and high levels of epinephrine (6). ...
... It is well understood that carbohydrate consumption before exercise leads to an increase in blood glucose levels, and this fuel source (glucose) is efficiently used for muscle contraction, but also inhibits fat oxidation (3,13,14,26,30). Conversely, training in a fasted state has been shown to stimulate the rate of lipolysis and fat oxidation (26,48), partly due to the low levels of insulin and high levels of epinephrine (6). At the cellular level, distinct differences in metabolism are observed when comparing fed and fasted conditions due to factors such as gene expression, acute hormonal changes, skeletal muscle glycogen content, and hepatic glycogen content. ...
Article
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Physique athletes often incorporate aerobic exercise as part of their exercise program to increase caloric expenditure for the purposes of improving their body composition. One method used by some physique competitors is to perform aerobic exercise in the fasted state under the assumption that low glycogen levels after an overnight fast allow for greater mobilization of stored fat to be used for fuel because carbohydrates are not readily available to produce energy. The purpose of this article is to examine the existing literature on the effect of fasted versus fed cardio on improving body composition for physique athletes.
... Taken collectively, these findings suggest that although the rate of lipolysis is important, the primary site of control of fatty acid oxidation during moderate to intense exercise resides at the muscle tissue level (18). Furthermore, increased glycolytic flux resulting from either CHO ingestion (19)(20)(21) and the concomitant rise in plasma insulin, or an increase in exercise intensity (14,15) directly inhibits LCFA oxidation. ...
Article
S19 Abstract Compared with the body's limited carbohydrate (CHO) stores, the reserves of fat in humans are plentiful: if fat was the sole source of energy, it could sustain skeletal muscle contraction for approximately 120 hours of continuous, moderate intensity (65% of maximal oxygen uptake [VO 2 max]) exercise. On the other hand, if CHO was the only fuel oxidised, it could provide energy for approximately 90 minutes of intense (85% of VO 2 max) activity. As the men's world record for the marathon (42.2 km) is approximately 125 minutes, this highlights the importance of fuel integration during exercise. In contrast to fatty acid metabolism, the rate of CHO oxidation during exercise is regulated tightly with glucose availability closely matching the requirements of the working muscles. Both the absolute (power output or speed) and relative (percentage of individual VO 2 max or maximal heart rate) intensity of exercise have important roles in the regulation of substrate metabolism: the absolute work rate or energy flux determines the total quantity of fuel required, while the relative intensity determines the fuel mix (i.e. the proportion of fat and CHO oxidised by the working muscles). During moderate exercise more than 50% of total energy is derived from fatty acid oxidation. However, during intense exercise, CHO fuels predominate with muscle glycogen and glucose utilisation scaling exponentially to the relative workrate. Although controversy exists with regard to the mechanism(s) that regulate substrate choice for oxidation by skeletal muscle during exercise, there is a growing body of evidence to suggest that CHO metabolism in general and muscle glycolytic flux in particular, regulate fatty acid oxidation by direct inhibition of long-chain fatty acid oxidation. CHO stores are limited and often substantially less than the requirements of the training and competition sessions undertaken by many athletes. Furthermore, muscle and liver glycogen depletion often coincide with fatigue during both endurance events and many team sports. Therefore, any nutritional strategy that promotes fatty acid oxidation and conserves endogenous CHO stores could, potentially, improve exercise capacity. (Aust J Nutr Diet 2001;58 Suppl 1:S19-S22)
... In contrast to the findings of the current study, several metabolic chamber studies of Melanson et al. showed no increase in 24-h fat oxidation with increased physical activity, when participants were in energy balance [59,60,173,174]. Because physical activity was performed in the postprandial state, the absence of an increase in 24-h fat oxidation in these studies was explained by an insulin-mediated decrease in lipolysis, that diminishes the supply of FFA [175]. FFA availability in plasma is a major determinant of fat oxidation in muscle during and after physical activity [176]. ...
Thesis
The classical concept of body weight regulation attributes the development of obesity to a chronically positive energy balance. There is, however, evidence indicating that beyond this basic concept, the effectiveness of body weight regulation is affected by the circadian regulation of metabolism and the level of energy flux (EF, level of energy balance). Meal skipping affects circadian regulation and might therefore also affect the regulation of body weight. In addition, an asymmetric regulation of body weight is hypothesized with improved effectiveness when EF is high (active lifestyle) and less effectiveness at a low EF (sedentary lifestyle). Metabolic chambers offer the opportunity to acquire short-term parameters of energy and macronutrient balance that precede long-term weight gain and therefore, can help to understand the impact of nutrition and physical activity interventions on body weight regulation. This thesis presents the implementation of a metabolic chamber system (Chapter II) and investigates the acute impact of meal skipping (Chapter III) and energy flux (Chapter IV) on energy and macronutrient metabolism by performing two well-controlled, cross-over intervention studies using metabolic chambers. The implementation of the metabolic chambers revealed, that thorough considerations must be made in terms of the metabolic chamber environment (room ventilation and position of analyzer unit), the additional devices (e.g. air conditioner) used as well as the study protocol, in order to obtain good data quality. The study on meal skipping includes 17 healthy participants who underwent 3 isocaloric 24-h interventions (55%, 30%, and 15% carbohydrate, fat and protein, respectively): a breakfast skipping day (BSD) and a dinner skipping day (DSD) separated by a conventional 3-meal-structure day (control). Energy and macronutrient balance were measured and postprandial glucose and insulin concentrations, as well as 24-h glycemia and 24-h insulin secretion (C-peptide), were analyzed. When compared with the 3-meal control, 24-h energy expenditure was higher on DSD (DSD: +69 kcal/d; p < 0.05), but not on BSD. Whereas, fat oxidation increased on the BSD only (+13 g/d; p < 0.01). Spontaneous physical activity, 24-h glycemia, and 24-h insulin secretion did not differ between intervention days. The postprandial homeostasis model assessment index (+54%) and glucose concentrations after lunch (+46%) were, however, higher on the BSD than on the DSD (both p < 0.05). When compared with 3 meals/d, dinner skipping increased energy expenditure. In contrast, higher postprandial insulin concentrations and increased fat oxidation with breakfast skipping show the development of metabolic inflexibility in response to prolonged fasting that may in the long-term lead to impaired glucose homeostasis. The study on energy flux includes 16 healthy participants who underwent three 24-h interventions with different levels of EF: (i) low EF, physical activity level (PAL) = 1.3 – 1.4 (ii) medium EF, PAL = 1.5 – 1.6 and (iii) high EF, PAL = 1.7 – 1.8 each at energy balance (EB), caloric restriction (CR), and overfeeding (OF) (100%, 75% and 125% of individual energy requirement with 50% carbohydrate, 35% fat, 15% protein). Different levels of EF were accomplished by walking (4 km/h) on a treadmill (0, 165 and 330 min). Sleeping energy expenditure (SEE), 24-h macronutrient oxidation and relative macronutrient balance (oxidation relative to intake) were determined. During EB and OF, 24-h fat oxidation increased with higher EF. This resulted in a higher relative fat balance at medium EF (EB: +17%, OF: +14%) and high EF (EB: +23%, OF: +17%) compared to low EF (all p < 0.05). SEE during EB and OF was higher at medium (EB: +5 kcal/3h and OF: +12 kcal/3h) and high (EB: +7 kcal/3h and OF: +18 kcal/3h) EF compared to low EF (all, p < 0.05). In contrast, during CR 24-h fat oxidation was only higher at high EF compared to low EF and neither relative fat balance nor SEE differed between the EF levels. A higher EF might have beneficial effects on body weight regulation during short-term overfeeding and energy balance because it increased SEE and improved relative fat balance. However, during short-term caloric restriction, a higher EF had no impact on the regulation of energy or fat balance. Therefore, a high EF especially can attenuate the adverse effects of short-term overfeeding. Altogether, this thesis emphasizes the importance of physical activity in daily life and suggests that the adverse metabolic outcome of breakfast skipping (caused by a positive energy balance after lunch with a preceding prolonged fasting period) might be attenuated by a high EF.
... CHO loading, pre-exercise meal, additional ergogenic aids, maintaining hydration status, and so on), even if the latter does not conform to the participant's habitual nutritional practices. The specific issue of fasted or fed trials is particularly challenging given that feeding before and/or during exercise can significantly alter metabolic responses to exercise [45]. As a highlighted example, it is well documented that the effects of exercise on cell signalling [46] or CHO feeding [47] and mouth rinsing [48] on exercise performance are more pronounced when exercise is commenced with low muscle glycogen availability and in the absence of a pre-exercise meal. ...
Article
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https://link.springer.com/article/10.1007/s40279-018-1005-2 Sport nutrition is one of the fastest growing and evolving disciplines of sport and exercise science, demonstrated by a 4-fold increase in the number of research papers between 2012 and 2018. Indeed, the scope of contemporary nutrition-related research could range from discovery of novel nutrient-sensitive cell-signalling pathways to the assessment of the effects of sports drinks on exercise performance. For the sport nutrition practitioner, the goal is to translate innovations in research to develop and administer practical interventions that contribute to the delivery of winning performances. Accordingly, step one in the translation of research to practice should always be a well-structured critique of the translational potential of the existing scientific evidence. To this end, we present an operational framework (the “Paper-2-Podium Matrix”) that provides a checklist of criteria for which to prompt the critical evaluation of performance nutrition-related research papers. In considering the (1) research context, (2) participant characteristics, (3) research design, (4) dietary and exercise controls, (5) validity and reliability of exercise performance tests, (6) data analytics, (7) feasibility of application, (8) risk/reward and (9) timing of the intervention, we aimed to provide a time-efficient framework to aid practitioners in their scientific appraisal of research. Ultimately, it is the combination of boldness of reform (i.e. innovations in research) and quality of execution (i.e. ease of administration of practical solutions) that is most likely to deliver the transition from paper to podium.
... Substrate utilization during exercise is also dependent on the intensity of physical activity as CHOs are the preferred energy source in high-intensity exercise, whereas during low-to-moderate intensity physical activity, the energy comes mainly from the catabolism of FFA. Nevertheless, preexercise glucose ingestion suppresses lipolysis to a point at which it limits fat oxidation, even during low-intensity exercise [94]. It seems that preexercise CHO meal can affect the typical intensity-dependent substrate utilization, probably by the CHO-induced rise in INS that inhibits the mobilization and hence availability of circulating FFA. ...
... El consumo de alimentos de bajo índice glucémico antes del ejercicio permitiría una absorción lenta de la glucosa en sangre, lo que podría mejorar la salud de los atletas a largo plazo (14). La oxidación de grasas sería menor durante el ejercicio, después del consumo de una comida rica en HC (15), debido al aumento de la secreción de insulina e inhibición de la lipólisis y la β-oxidación de manera significativa. Algunos autores han concluido que el consumo de HC antes del ejercicio aumentaría significativamente la tasa de intercambio respiratorio en comparación a condiciones de ayuno (5). ...
Article
Introduction: The effect of exercise on fat-acid oxidation depends on its intensity and duration. Pre-training ingest of carbohydrates (CH) decreases the rate of fat oxidation. In contrast, the effect of pre-consumption of monounsaturated fatty acids (MUFA) is less known. Objective: the aim of this study was to compare the effect of pre-consumption of two isocaloric snacks in a standardized exercise session during a period of nine weeks and to quantify their impact in the fat oxidation and decrease of fat mass in healthy and physically active adults. Methods: randomized, placebo-control clinical trial study. A total of 19 subjects between 20 and 39 years old were randomly distributed in three groups: CH group, with snack of high content of complex CH; FAT group, with snack of high content of MUFA; and control group, with a minimum fast for three hours before the training session. The measurements were rate of fat oxidation, body composition, and endurance training with continuing and intervallic modalities. Results: the control group showed a tendency to fat mass decrease at the end of the intervention. The fat oxidation of group had a higher tendency than the CH and control group, before and after the intervention. Nevertheless, statistical differences of fat oxidation were not found between the groups. Conclusions: the fat oxidation and the decrease of fat mass may not be influenced by the type of food previously consumed before exercise.
... Higher carbohydrate intake was associated with a reduced MFO, which echoed controlled short-term dietary manipulation studies in which marked isoenergetic increases in dietary carbohydrate decreased FAT-OX (14,32,33). This result likely reflected a direct influence of carbohydrate intake on its subsequent availability for oxidation during exercise (32) or the related antilipolytic effect of insulin (34). An increase of glycolytic flux during exercise (e.g., with high exercise intensities or increased carbohydrate provision) can also directly downregulate mitochondrial long-chain FAT-OX (35,36). ...
Article
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Background: Substantial interindividual variability exists in the maximal rate of fat oxidation (MFO) during exercise with potential implications for metabolic health. Although the diet can affect the metabolic response to exercise, the contribution of a self-selected diet to the interindividual variability in the MFO requires further clarification. Objective: We sought to identify whether recent, self-selected dietary intake independently predicts the MFO in healthy men and women. Design: The MFO and maximal oxygen uptake (O2 max) were determined with the use of indirect calorimetry in 305 healthy volunteers [150 men and 155 women; mean ± SD age: 25 ± 6 y; body mass index (BMI; in kg/m²): 23 ± 2]. Dual-energy X-ray absorptiometry was used to assess body composition with the self-reported physical activity level (SRPAL) and dietary intake determined in the 4 d before exercise testing. To minimize potential confounding with typically observed sex-related differences (e.g., body composition), predictor variables were mean-centered by sex. In the analyses, hierarchical multiple linear regressions were used to quantify each variable’s influence on the MFO. Results: The mean absolute MFO was 0.55 ± 0.19 g/min (range: 0.19–1.13 g/min). A total of 44.4% of the interindividual variability in the MFO was explained by the O2 max, sex, and SRPAL with dietary carbohydrate (carbohydrate; negative association with the MFO) and fat intake (positive association) associated with an additional 3.2% of the variance. When expressed relative to fat-free mass (FFM), the MFO was 10.8 ± 3.2 mg · kg FFM⁻¹ · min⁻¹ (range: 3.5–20.7 mg · kg FFM⁻¹ · min⁻¹) with 16.6% of the variability explained by the O2 max, sex, and SRPAL; dietary carbohydrate and fat intakes together explained an additional 2.6% of the variability. Biological sex was an independent determinant of the MFO with women showing a higher MFO [men: 10.3 ± 3.1 mg · kg FFM⁻¹ · min⁻¹ (3.5–19.9 mg · kg FFM⁻¹ · min⁻¹); women: 11.2 ± 3.3 mg · kg FFM⁻¹ · min⁻¹ (4.6–20.7 mg · kg FFM⁻¹ · min⁻¹); P < 0.05]. Conclusion: Considered alongside other robust determinants, dietary carbohydrate and fat intake make modest but independent contributions to the interindividual variability in the capacity to oxidize fat during exercise. This trial was registered at clinicaltrials.gov as NCT02070055.
... The consumption of low-GI compared to moderate-or high-GI carbohydrates results in lower and more stable glucose and insulin response. Therefore, low-GI foods could be superior for stimulating fat oxidation and reducing carbohydrate oxidation during exercise because insulin inhibits fat oxidation ( Horowitz et al., 1997). The blood glucose response to the moderate-GI bar in our study, however, was not significantly different than the low-GI bar (Figure 2a), which differed from our previous determination of a significantly higher glucose response in the moderate-GI bar (Chilibeck et al., 2011). ...
Article
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Low-glycemic index carbohydrates are potentially better for endurance performance as they result in greater fat oxidation and lower carbohydrate oxidation due to lower insulin release. We compared the effects of pre-exercise feeding with a low-glycemic index lentil-based sports nutrition bar, a commercially-available sports nutrition bar with moderate-glycemic index, and a non-caloric placebo on metabolism and performance during endurance cycling (Trial 1). Using a randomized, counterbalanced, crossover design, endurance-trained individuals (n = 11; eight males; 26 ± 6y; VO2peak 51.4 ± 1.6 mL/kg/min) consumed 1.5 g/kg available carbohydrate from a lentil bar and a moderate-glycemic index bar, as well as a placebo, 1h before endurance cycling (75 min at 65% VO2peak, followed by a 7 km time trial). We also compared post-exercise consumption of the low-glycemic index bar with another moderate-glycemic index bar on next-day exercise performance as an assessment of recovery (Trial 2). In Trial 1, fat or carbohydrate oxidation rates were not different between the bar conditions (p > 0.05). Blood lactate was lower during the low-versus the moderate-glycemic index condition after 75 minutes of cycling (2.6 versus 4.0 mmol/L, p < 0.05) and at the end of the time trial (7.4 versus 9.1 mmol/L, p < 0.05). Time trial performance improved (p < 0.05) after consumption of the low-(574 ± 55 s) and moderate-glycemic index (583 ± 59 s) bars compared to the placebo (619 ± 81 s). In Trial 2 (next-day recovery), performance improved (p < 0.05) with the low-glycemic index bar (547 ± 42 s) compared to the moderate-glycemic index bar (569 ± 42 s) and the placebo (566 ± 34 s). Low-and moderate-2 glycemic index sports nutrition bars improved cycling exercise performance; however, only the low-glycemic index bar improved next day performance.
... In the evening, after the HCD dinner meal, there was also a decrease of the levels of several metabolites related primarily to lipid metabolism and to a lesser extent amino acid ( Figure 2I, Fig. S3C,D, and Table S5). The consumption of carbohydraterich meals and the associated rise in plasma insulin concentrations suppresses lipolysis for several hours post-ingestion [29], and explains why lipid metabolites were downregulated following the HCD. ...
Article
Objective Advances in the field of metabolomics and the concomitant development of bioinformatics tools constitute a promising avenue towards the development of precision medicine and personalized profiling for numerous disease states. Studies in animal models have strengthened this concept, but the application in human subjects is scarce. Methods Utilizing high-throughput metabolomics, we have analyzed the metabolome levels of human serum and skeletal muscle in the morning and evening in response to divergent nutritional challenges in order to identify unique signatures present in serum and muscle. Results We reveal dynamic daily variation of human metabolome unique to serum and muscle. The overall effect of nutritional challenges on the serum and muscle metabolome results in a profound rewiring of morning-evening metabolic profiles in human participants in response to the timing and type of dietary challenge. Conclusion We highlight time-of-day and meal-composition dependence of reprogramming of human metabolome by nutritional challenges.
... This is likely explained by carbohydrate-induced insulinaemia, suppression of lipolysis, and suppression of fatty acid availability, which in turn might be expected to suppress whole-body fat oxidation in a manner similar to that seen at high exercise intensities ( Romijn et al., 1995). Indeed, triglyceride and heparin infusion has been shown to increase plasma NEFA concentration, whole-body lipolysis, and fat oxidation rate during exercise with pre- exercise glucose feeding toward values observed during exercise after an overnight fast, suggesting that part of the suppressive effect of pre-exercise carbohydrate feeding on whole-body fat oxidation is explained by reduced fatty acid availability ( Horowitz et al., 1997). Acute nutritional status is therefore a clear determinant of MFO and Fat max , and should be considered when comparing results between-studies as well as in serial intra-individual assessment. ...
Article
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Using a short-duration step protocol and continuous indirect calorimetry, whole-body rates of fat and carbohydrate oxidation can be estimated across a range of exercise workloads, along with the individual maximal rate of fat oxidation (MFO) and the exercise intensity at which MFO occurs (Fatmax). These variables appear to have implications both in sport and health contexts. After discussion of the key determinants of MFO and Fatmax that must be considered during laboratory measurement, the present review sought to synthesize existing data in order to contextualize individually measured fat oxidation values. Data collected in homogenous cohorts on cycle ergometers after an overnight fast was synthesized to produce normative values in given subject populations. These normative values might be used to contextualize individual measurements and define research cohorts according their capacity for fat oxidation during exercise. Pertinent directions for future research were identified.
... While there are situations in which the glucose-fatty acid cycle operates, a series of elegant studies conducted in the late 1990s clearly demonstrated that carbohydrate availability directly regulates fat oxidation at rest and during exercise Horowitz et al. 1997;Romijn et al. 1995). Coyle et al. (1997) demonstrated that a carbohydrate-rich meal that induced hyperglycemia and hyperinsulinemia increased glycolytic flux and directly reduced rates of FA oxidation during low-intensity exercise. ...
Chapter
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Exercise training-induced adaptations in human skeletal muscle are largely determined by the mode, volume, intensity and frequency of the training stimulus. However, a growing body of evidence demonstrates that the availability of endogenous and exogenous macronutrients can modify multiple intramuscular responses to both endurance- and resistance-based exercise. Acutely manipulating substrate availability (by altering diet composition and/or timing of meals) rapidly alters the concentration of blood-borne substrates and hormones that modulate several receptor-mediated signaling pathways. The release of cytokines and growth factors from contracting skeletal muscle also stimulates cell surface receptors and activates many intracellular signaling cascades. These local and systemic factors cause marked perturbations in the storage profile of skeletal muscle (and other insulin-sensitive tissues) that, in turn, exert pronounced effects on resting fuel metabolism and patterns of fuel utilization during exercise. When repeated over weeks and months, such nutrient-exercise interactions have the potential to alter numerous adaptive processes in skeletal muscle that ultimately drive the phenotype-specific variability observed between individuals. One strategy that augments endurance-training adaptation is commencing exercise with low muscle glycogen concentration (“train-low”). The amplified training response observed with low endogenous carbohydrate availability is likely regulated by enhanced activation of key cell signalling kinases (e.g., AMPK, p38MAPK), transcription factors (e.g., p53, PPARδ) and transcriptional co-activators (e.g., PGC-1α), such that a coordinated up-regulation of both the nuclear and mitochondrial genomes occurs. This chapter provides a contemporary perspective of our understanding of the molecular and cellular events that take place in skeletal muscle in response to exercise commenced after alterations in nutrient availability and discusses how the ensuing hormonal milieu interacts with specific contractile stimulus to modulate many of the acute responses to exercise, thereby potentially promoting or inhibiting subsequent training adaptation.
... Aç karnına yapılan egzersizde dolaşımda düşük insülin seviyesi ve yüksek plazma epinefrin seviyesi görülürken (Arkinstall et al., 2001;De Bock et al., 2005;Febbraio et al., 2000), adipoz dokudaki lipolizde ve periferal yağ oksidasyonunda artış olur (Horowitz et al, 1997). ...
... The slower rise in blood glucose after consumption of low-glycemic index (GI) carbohydrates results in a lower increase in insulin [2]. This is important for endurance athletes because high insulin levels inhibit fatty-acid oxidation [3] increasing the muscle's reliance on carbohydrate oxidation and potentially resulting in increased glycogen usage [2]. Consumption of low-GI carbohydrates may therefore provide enhancement of endurance exercise performance compared to high-GI carbohydrates [4]. ...
Poster
Tart cherry consumption may have a favorable impact on exercise performance in endurance athletes through its anti-inflammatory roles and low glycemic index (GI). Low GI foods may be of benefit for endurance athletes because of the slow release of glucose into the blood after digestion. However, no study has measured the GI of tart cherry juice to see if the low GI of tart cherries is affected by processing. The purpose of this study was to evaluate the GI of raw tart cherries and juice from tart cherries to see if the low GI is preserved when raw cherries are processed into juice. Seven participants (6 females, 1 male, 28±5 y, 62.6±13.2 kg, 165±6 cm) visited our lab on four different occasions with each visit separated by a week and preceded by a 10 hour fast. Participants consumed a glucose standard (250 mL water with 25 g glucose) during the first two visits and then 167 g raw cherries+250 mL water or 189 mL of cherry juice+89 mL of water for the last two conditions. Blood glucose was measured at baseline and at 15, 30, 45, 60, 90, and 120 minutes following consumption. Glycemic index was determined by dividing the incremental area under the curve (iAUC) of the blood glucose response of the cherries or juice by the iAUC for the glucose standard. The GI of the raw cherries (46±39) was not significantly different from the juice (45±27), p>0.05, with both being classified as “low” GI (i.e. GI≤55). The GI of raw cherries is low and a low GI can be maintained in cherry juice form. (Supported by the Canadian Cherry Producers Incorporated.)
... Therefore, it is likely that elevated plasma fatty acids during the first hour of recovery resulted in an increased uptake and oxidation of fatty acids within glycogen-depleted muscle. This is supported by the rapid decline in plasma fatty acid levels early in recovery, which can probably be attributed to both the rapid clearance by peripheral tissues, including skeletal muscle, as well as an insulin-mediated reduction in peripheral lipolysis (Horowitz et al. 1997;Mittendorfer et al. 2002) following the first high-CHO meal during recovery. It is paradoxical, though, that fat oxidation remained elevated in the presence of elevated insulin levels. ...
... The responses to fuel supply and oxidation during fasting are well documented [15]. For example, fasting before and during exercise is associated with low circulating insulin levels, elevated plasma epinephrine concentrations [17,18], increased rate of adipose tissue lipolysis, peripheral fat oxidation [19] and reduced availability of blood glucose [17]. Two recent studies using SIT and fasting [20,21] and previous studies using continuous cycling [22,23] have observed reductions in blood glucose (GLU) and triglyceride (TG) levels following acute bouts of exercise. ...
Article
Full-text available
Purpose The aim of this study was to investigate the effects of sprint interval training (SIT) and feeding state [fasted (FAST) or fed (FED)] on metabolic and cardiorespiratory parameters. Methods Twelve active men (age 23 ± 3 years; body mass 76.43 ± 4.06 kg; height 175.6 ± 4.98 cm; body mass index 24.78 ± 0.56 kg/m²; VO2peak 52.33 ± 4.87 mL/min/kg) volunteered to participate in this study. Participants completed a 2-week SIT intervention, comprising two randomized sessions (FAST, FED) of three bouts of 30-s Wingate anaerobic sprints on an electromagnetically braked cycle, with 4 min of rest interspersed between bouts. Metabolic and cardiorespiratory assessments were repeated every 10 min during the 1 h post-intervention time period. Results The rating of perceived exertion was higher in the FAST condition as compared to FED during bout 3 (20 ± 0.0 vs. 19.42 ± 0.51; p ≤ 0.05). There was no difference in peak power, mean power and minimum power during the SIT protocol in FAST and FED conditions. Glucose values were lower 10, 20, 30, 40 and 50 min following SIT than during bouts 1–3 in the FED condition, whereas glucose values remained stable during all time points in the FAST state. Triglycerides and cholesterol remained unchanged following SIT as compared to pre-exercise in both conditions. Compared to pre-exercise, respiratory exchange ratio was higher 10 and 20 min, and lower 40, 50 and 60 min post-exercise in the FAST condition and was higher at all time points in the FED condition. Conclusions SIT in the fasted state does not decrease muscle performance and increase fat oxidation 30 min post-exercise without optimizing energy expenditure in healthy active men.
... It is, of course, difficult to draw accurate conclusions on rates of lipolysis based on measurements of circulating glycerol and NEFA per se. Nonetheless, on the basis of statistical differences in plasma NEFA concentrations between trials immediately post PM HIT and consistent with the well-documented effects of CHO feeding (Horowitz et al. 1997), it is assumed that lipolysis was suppressed in the HCHO trial compared to both the LCAL and LCHF trials. The fact that plasma glycerol did not display statistical differences between trials may also be potentially reflective of greater glycerol uptake by the liver in both the LCAL and LCHF trials in order to provide a gluconeogenic substrate to maintain plasma glucose concentration (Ahlborg et al. 1974;Jensen et al. 2001). ...
Article
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Key points: Reduced carbohydrate (CHO) availability before and after exercise may augment endurance training-induced adaptations of human skeletal muscle, as mediated via modulation of cell signalling pathways. However, it is not known whether such responses are mediated by CHO restriction, energy restriction or a combination of both. In recovery from a twice per day training protocol where muscle glycogen concentration is maintained within 200-350 mmol.kg-1 dw, we demonstrate acute post-exercise CHO and energy restriction (i.e. <24 hours) does not potentiate potent cell signalling pathways that regulate hallmark adaptations associated with endurance training. In contrast, consuming CHO before, during and after an acute training session attenuated markers of bone resorption, effects that are independent of energy availability. Whilst the enhanced muscle adaptations associated with CHO restriction may be regulated by absolute muscle glycogen concentration, the acute within day fluctuations in CHO availability inherent to twice per day training may have chronic implications for bone turnover. Abstract: We examined the effects of post-exercise carbohydrate (CHO) and energy availability (EA) on potent skeletal muscle cell signalling pathways (regulating mitochondrial biogenesis and lipid metabolism) and indicators of bone metabolism. In a repeated measures design, nine males completed a morning (AM) and afternoon (PM) high-intensity interval (HIT) (8 × 5-min at 85% VO2peak ) running protocol (interspersed by 3.5 hours) under dietary conditions of 1) high CHO availability (HCHO: CHO ∼12 g.kg-1 , EA∼ 60 kcal.kg-1 FFM), 2) reduced CHO but high fat availability (LCHF: CHO ∼3 g.kg-1 , EA∼ 60 kcal.kg-1 FFM) or 3), reduced CHO and reduced energy availability (LCAL: CHO ∼3 g.kg-1 , EA∼ 20 kcal.kg-1 FFM). Muscle glycogen was reduced to ∼200 mmol.kg-1 dw in all trials immediately post PM-HIT (P < 0.01) and remained lower at 17-h (171, 194 and 316 mmol.kg-1 dw) post PM-HIT in LCHF and LCAL (P < 0.001) compared to HCHO. Exercise induced comparable p38MAPK phosphorylation (P < 0.05) immediately-post PM-HIT and similar mRNA expression (all P < 0.05) of PGC-1α, p53 and CPT1 mRNA in HCHO, LCHF and LCAL. Post-exercise circulating βCTX was lower in HCHO (P < 0.05) compared to LCHF and LCAL, whereas exercise-induced increases in IL-6 were larger in LCAL (P < 0.05) compared to LCHF and HCHO. In conditions where glycogen concentration is maintained within 200-350 mmol.kg-1 dw, we conclude post-exercise CHO and energy restriction (i.e. < 24 hours) does not potentiate cell signalling pathways that regulate hallmark adaptations associated with endurance training. In contrast, consuming CHO before, during and after HIT running attenuates bone resorption, effects that are independent of energy availability and circulating IL-6. This article is protected by copyright. All rights reserved.
... However, several studies have shown reduced rates of fat oxidation during exercise following ingestion of carbohydrates (see Wu et al. 2003). This is mainly due to hyperglycaemia and hyperinsulinaemia during the postprandial period, which exert inhibition of lipolysis and lipid oxidation within the muscles Horowitz et al. 1997). Wu et al. (2003) have shown that a carbohydrate meal three hours before exercise resulted in lower rates of fat oxidation during subsequent exercise than when exercise is performed in the fasting state. ...
... There are, of course, advantages and disadvantages to many of the common dietary standardization methods outlined above, including cost and ease of intervention but also the ecological validity to the research participants. Fasting is often utilized as a control for dietary intervention studies given that feeding around exercise can significantly alter metabolic responses pre-, during, and post-exercise (Bartlett et al., 2013;Horowitz et al., 1997;Lane et al., 2013;Widrick et al., 1993). However, it is unlikely that elite athletes would compete or, indeed, undertake consecutive aerobic and resistance training sessions in the fasted state or without energy intake between sessions; again, caution should be taken when translating research from studies on fasted participants to athletes intending to compete in the fed state. ...
Article
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• Sport nutrition is one of the fastest growing and evolving disciplines of sport and exercise science with research ranging from the discovery of novel nutrient sensitive cell signaling pathways to the effects of sports drinks on ratings of perceived effort. • Sport nutritionists often utilize both classic and contemporary literature to help guide their applied practice, ultimately hoping that the research can help to fuel winning performances. • Step one in the translation of research to practice should always be a well-structured critique of the translational potential of the existing scientific evidence. • We present an operational framework (the paper to podium matrix) providing a checklist of criteria to prompt the critical evaluation of performance nutrition related research papers. • It is the combination of boldness of reform (i.e., innovations in research) and quality of execution (i.e., ease of administration of practical solutions) that is most likely to deliver the transition from paper to podium.
... Furthermore, compared with 0.0 g·min −1 , 0.5-, 1.0-, and 1.5-g·min −1 PHY doses had similar and ∼10% lower whole-body fat oxidation rates (Table 2), demonstrating the preference of exercising muscle for exogenous CHO at least in these endurance-trained individuals. This could be due to differences in circulating insulin concentration (22) as insulin is a potent inhibitor of lipolysis (23). In addition, greater PHY oxidation resulted in a significantly lower (P < 0.05) endogenous CHO oxidation rate at the 1-g·min −1 dose compared with those of both 0.0-g·min −1 and 0.5-g·min −1 doses ( Table 2) Phytoglycogen Oxidation in Endurance-Trained Men 5 at 1 g·min −1 compared with 0.0 g·min −1 reduced endogenous CHO use by ∼43%. ...
Article
Full-text available
Background Phytoglycogen (PHY; PhytoSpherix; Mirexus Biotechnologies), a highly branched polysaccharide extracted from sweet corn, has considerable potential for exercise oxidation due to its low viscosity in water, high water retention, and exceptional stability. Objectives Using gas chromatography–isotope ratio mass spectrometry, we investigated dose–response oxidation of ingested PHY during prolonged, moderate-intensity exercise. Methods Thirteen men (≥1 y endurance-training experience, ≥6 d·wk−1, ∼1–1.5 h·d−1; age, 25.7 ± 5.5 y; mass, 79.3 ± 10.0 kg; V̇O2max, 59.9 ± 5.5 mL·kg−1·min−1; means ± SDs) cycled for 150 min (50% maximal watt output) while ingesting PHY concentrations of 0.0% (0.0 g·min−1), 3.6% (0.5 g·min−1), 7.2% (1.0 g·min−1), 10.8% (1.5 g·min−1), or 14.4% (2 g·min−1) in water (2100 mL) (n = 7–10/dose). Substrate oxidation was determined using stable-isotope methods and indirect calorimetry. Results PHY oxidation plateaued between 60 and 150 min of exercise and increased (P < 0.001) from 0.49 to 0.72 g·min−1 with 0.5- and 1.0-g·min−1 doses without further increases (0.76 and 0.73 g·min−1; P > 0.05) with 1.5 or 2 g·min−1. Peak PHY oxidation (0.84 ± 0.04 g·min−1) occurred in the final 30 min of exercise with 2 g·min−1. Exercise blood glucose was greater (5.1 mmol·L−1) with 1.0-, 1.5-, and 2-g·min−1 doses compared with that of 0.5 (4.7 mmol·L−1) or 0.0 g·min−1 (4.2 mmol·L−1) (P < 0.0001). Gastrointestinal distress was minimal except with 2 g·min−1 (P < 0.001). Conclusions In male endurance athletes, PHY oxidation plateaued at 0.72–0.76 g·min−1 during 150 min of cycling at 50% Wmax (peak oxidation of 0.84 g·min−1 occurred during the final 30 min). This trial was registered at clinicaltrials.gov as NCT02909881.
... Furthermore, the pre-exercise hyperinsulinemia and the accompanied drop of blood glucose have also been associated with an increased muscle glycogenolysis (9,15). This is accompanied by a depression of free fatty acids (FFA) (10,12,13,23,24,27,28,36,38) and lipolysis (17), and a premature onset of fatigue (12). On the other hand, the majority of studies have reported either no effect or an improvement in endurance performance as a result of pre-exercise CHO feeding (33). ...
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This study examined the phenomenon of transient hypoglycemia and metabolic responses to pre-exercise carbohydrate (CHO) maltodextrin ingestion in cycling and running on the same individuals. Eleven active males cycled or ran for 30 min at 80% maximal heart rate (HRmax) after ingestion of either 1g/kg body mass maltodextrin (CHO-Cycle and CHO-Run respectively) or placebo (PL-Cycle and PL-Run) solutions. Fluids were ingested 30min before exercise in a double-blind and random manner. Blood glucose and serum insulin were higher before exercise in CHO (mean CHO-Cycle+CHO-Run) (Glucose: 7.4 ± 0.3 mmol. l-1 ; Insulin: 59 ± 10 mU. l-1) compared to placebo (mean PL-Cycle+PL-Run) (Glucose: 4.7 ± 0.1 mmol. l-1 ; Insulin: 8 ± 1 mU. l-1) (p<0.01), but no differences were observed during exercise among the 4 conditions. Mean blood glucose did not drop below 4.1 mmol. l-1 in any trial. However, six volunteers in CHO-Cycle and seven in CHO-Run experienced blood glucose concentration < 3.5 mmol. l-1 at 20min of exercise and similar degree of transient hypoglycemia in both exercise modes. No association was found between insulin response to maltodextrin ingestion and drop in blood glucose during exercise. Blood lactate increased with exercise more in cycling compared to running, and plasma free fatty acids (FFA) concentrations were higher in placebo compared to CHO irrespective of exercise mode (p<0.01). The ingestion of maltodextrin 30min before exercise at about 80% HRmax produced similar glucose and insulin responses in cycling and running in active males. Lactate was higher in cycling, whereas maltodextrin reduced FFA concentrations independently of exercise mode.
... Here our emphasis will be placed on the applications of stable isotope tracer methodology owing mainly to (1) safety issues, particularly for humans and (2) the versatility of stable isotope tracers in assessing various aspects of metabolism [7,15,16,[29][30][31][32][33][34][35]. In addition, assessments of metabolic flux using stable isotope tracer methodology are typically accomplished in conjunction with the use of gas or liquid chromatography mass spectrometry (GC-or LC-MS) [36,37] or magnetic resonance spectroscopy [38,39] with essentially the same purpose: i.e., determining tracer enrichment (e.g., magnitude of labeling, expressed as various ways) [15,16], which will be briefly discussed below. ...
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Like other substrates, plasma glucose is in a dynamic state of constant turnover (i.e., rates of glucose appearance [Ra glucose] into and disappearance [Rd glucose] from the plasma) while staying within a narrow range of normal concentrations, a physiological priority. Persistent imbalance of glucose turnover leads to elevations (i.e., hyperglycemia, Ra>Rd) or falls (i.e., hypoglycemia, Ra<Rd) in the pool size, leading to clinical conditions such as diabetes. Endogenous Ra glucose is divided into hepatic glucose production via glycogenolysis and gluconeogenesis (GNG) and renal GNG. On the other hand, Rd glucose, the summed rate of glucose uptake by tissues/organs, involves various intracellular metabolic pathways including glycolysis, the tricarboxylic acid (TCA) cycle, and oxidation at varying rates depending on the metabolic status. Despite the dynamic nature of glucose metabolism, metabolic studies typically rely on measurements of static, snapshot information such as the abundance of mRNAs and proteins and (in)activation of implicated signaling networks without determining actual flux rates. In this review, we will discuss the importance of obtaining kinetic information, basic principles of stable isotope tracer methodology, calculations of in vivo glucose kinetics, and assessments of metabolic flux in experimental models in vivo and in vitro.
... While there are situations in which the glucose-fatty acid cycle operates, a series of elegant studies conducted in the late 1990s clearly demonstrated that carbohydrate availability directly regulates fat oxidation at rest and during exercise Horowitz et al. 1997;Romijn et al. 1995). Coyle et al. (1997) demonstrated that a carbohydrate-rich meal that induced hyperglycemia and hyperinsulinemia increased glycolytic flux and directly reduced rates of FA oxidation during low-intensity exercise. ...
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The world is faced with an epidemic of metabolic diseases such as obesity and type 2 diabetes. This is due to changes in dietary habits and the decrease in physical activity. Exercise is usually part of the prescription, the first line of defense, to prevent or treat metabolic disorders. However, we are still learning how and why exercise provides metabolic benefits in human health. This open access volume focuses on the cellular and molecular pathways that link exercise, muscle biology, hormones and metabolism. This will include novel “myokines” that might act as new therapeutic agents in the future.
... The slower rise in blood glucose after consumption of low-glycemic index (GI) carbohydrates results in a lower increase in insulin [2]. This is important for endurance athletes because high insulin levels inhibit fatty-acid oxidation [3] increasing the muscle's reliance on carbohydrate oxidation and potentially resulting in increased glycogen usage [2]. Consumption of low-GI carbohydrates may therefore provide enhancement of endurance exercise performance compared to high-GI carbohydrates [4]. ...
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Objective. — Endurance athletes may benefit from consuming foods low in glycemic index (GI) before sport performance. Foods such as lentils and tart cherries have a very low GI, but processing these ingredients into products that can easily be consumed before performance may affect their GI. The study determined whether processing lentils into a sports nutrition bar and tart cherries into a drink affected the glycemic index. Methods. — Using a randomized counterbalanced design, we compared the GI of a lentil-based sports nutrition bar (n = 10) to two versions of a popular sports nutrition bar (i.e. Power Bar Harvest and Power Bar Recovery, n = 9) in young, healthy individuals. We then evaluated the GI of raw tart cherries and juice from tart cherries in another group of young healthy individuals (n=7). Results. — The lentil-based sports nutrition bar had a lower GI than the other bars (i.e. 45 ± 17 versus 55 ± 13 and 55 ± 14 for the lentil bar, Power Bar Harvest and Power Bar Recovery, respec- tively; p < 0.05), and all were classified as having a low GI. The GI of raw cherries was also low (46 ± 39) and processing the cherries into a juice did not affect the GI (45 ± 27, p > 0.05). Conclusions. — A sports nutrition bar with lentils as a main ingredient or cherry juice offer low GI carbohydrate options for endurance athletes.
... The inability to switch efficiently between fuel sources when transitioning between postabsorptive and postprandial stages (metabolic inflexibility) can be explained, in part by differences in glucose disposal rate (Galgani et al. 2008a) and the capacity to increase nonoxidative glucose disposal (Dube et al. 2014). Additionally, the capacity for insulin to suppress lipolysis, and thereby fat oxidation, in the postprandial period is critical for glucose uptake and MF (Horowitz et al. 1997;Galgani et al. 2008a;Sparks et al. 2009). Substrate transport in the postprandial state is, in large part, mediated by the vascular actions of insulin to increase microvascular blood flow (Baron et al. 2000). ...
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We assessed metabolic flexibility (MF) via a mixed meal in a group of young, healthy participants with a positive family history of maternal type 2 diabetes (T2D) (FH+) and those without a family history of T2D (FH−) under three distinct conditions; baseline (BL; no previous exercise), 1‐h post high intensity interval exercise (1H), and 48‐h post exercise recovery. On separate visits, participants completed a single bout of high intensity interval exercise (HIIE) and repeated the MMTT 1‐h (1H) and 48 h (48H) postexercise. FH+ participants were not able to suppress fat oxidation 1‐h post exercise (1H) as effectively as FH− participants were, however, this response was improved when measured at the 48H visit. Insulin AUC was significantly lowered at both 1H and 48H when compared to the BL visit. Serum NEFA AUC was elevated 1‐h post exercise, when compared to BL, but was significantly reduced at the 48H visit. Young, healthy participants with a maternal history of T2D demonstrate impaired MF (related to the inability to suppress fat oxidation) in response to acute HIIE (1H) that was improved 48H. The overall effect of HIIE showed improved insulin AUC and NEFA AUC up to 48H post that did not differ by FH. Young, healthy men and women with a positive maternal history of type 2 diabetes demonstrate an impaired postprandial reduction in fat oxidation after a bout of high‐intensity interval exercise. However, 48 h postexercise, this response is improved in conjunction with enhanced suppression of postprandial lipolysis.
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Fasting is defined as the abstinence from consuming food and/or beverages for different periods of time. Both traditional and modern healthcare systems recommend fasting as a therapeutic intervention for the management of several chronic, non-infectious diseases. Exercising during a fasting state increases lipolysis in adipose tissue while also stimulating peripheral fat oxidation, resulting in increased fat utilization and weight loss. A key focus of this review is to assess whether endurance training performed while fasting induces specific training adaptations, where increased fat oxidation improves long-term endurance levels. Fasting decreases body weight, lean body and fat content in both trained and untrained individuals. Several studies indicate a broader impact of fasting on metabolism, with effects on protein and glucose metabolism in sedentary and untrained subjects. However, there are conflicting data regarding the effects of fasting on glucose metabolism in highly trained athletes. The effects of fasting on physical performance indicators also remain unclear, with some reporting a decreased performance, while others found no significant effects. Differences in experimental design, severity of calorie restriction, duration, and participant characteristics could, at least in part, explain such discordant findings. Our review of the literature suggests that there is little evidence to support the notion of endurance training and fasting-mediated increases in fat oxidation, and we recommend that endurance athletes should avoid high intensity training while fasting.
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The primary variables influencing the adaptive response to a bout of endurance training are exercise duration and exercise intensity. However, altering the availability of nutrients before and during exercise can also impact the training response by modulating the exercise stimulus and/or the physiological and molecular responses to the exercise-induced perturbations. The purpose of this review is to highlight the current knowledge of the influence of pre-exercise nutrition ingestion on the metabolic, physiological, and performance responses to endurance training and suggest directions for future research. Acutely, carbohydrate ingestion reduces fat oxidation, but there is little evidence showing enhanced fat burning capacity following long-term fasted-state training. Performance is improved following pre-exercise carbohydrate ingestion for longer but not shorter duration exercise, while training-induced performance improvements following nutrition strategies that modulate carbohydrate availability vary based on the type of nutrition protocol used. Contrasting findings related to the influence of acute carbohydrate ingestion on mitochondrial signaling may be related to the amount of carbohydrate consumed and the intensity of exercise. This review can help to guide athletes, coaches, and nutritionists in personalizing pre-exercise nutrition strategies, and for designing research studies to further elucidate the role of nutrition in endurance training adaptations.
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Insulin resistance is a key etiological factor in promoting not only type 2 diabetes mellitus but also cardiovascular disease (CVD). Exercise is a first-line therapy for combating chronic disease by improving insulin action through, in part, reducing hepatic glucose production and lipolysis as well as increasing skeletal muscle glucose uptake and vasodilation. Just like a pharmaceutical agent, exercise can be viewed as a “drug” such that identifying an optimal prescription requires a determination of mode, intensity, and timing as well as consideration of how much exercise is done relative to sitting for prolonged periods (e.g., desk job at work). Furthermore, proximal nutrition (nutrient timing, carbohydrate intake, etc.), sleep (or lack thereof), as well as alcohol consumption are likely important considerations for enhancing adaptations to exercise. Thus, identifying the maximal exercise “drug” for reducing insulin resistance will require a multi-health behavior approach to optimize type 2 diabetes and CVD care.
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Til tross for at både lav endogen og eksogen karbohydrattilgjengelighet kan være negativt for å opprettholde spesielt høy treningsintensitet, har flere studier demonstrert en potent effekt av tilsiktede perioder med redusert karbohydrattilgang på akutte treningsinduserte cellulære tilpasninger. Mer spesifikt er det observert effekter på cellesignalisering og genekspresjon-responser som regulerer grunnleggende utholdenhetsadaptasjoner. Det er flere metoder og konsepter som benyttes for å indusere disse responsene, deriblant trening fastende, doble treningsøkter på samme dag, og restriksjon av karbohydrater før søvn etterfulgt av trening morgenen etter (såkalt «sleep low»). Denne artikkelen har derfor som mål å beskrive litteraturens nåværende status omkring karbohydratperiodisering, og basert på dette gi konkrete råd om hvordan strategier for dette kan gjennomføres på en vellykket måte. Ikke minst er et mål å vurdere om ulike former for karbohydratperiodisering faktisk leder til bedre idrettsprestasjon sammenlignet med et jevnlig høyt inntak av karbohydrater.
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Die Ernährung des Sportlers stellt neben dem Training eine wichtige Grundlage für die sportliche Leistungsfähigkeit dar. Dabei geht es nicht nur um eine ausreichende Versorgung des Sportlers hinsichtlich des Energie- bzw. Makro- und Mikronährstoffbedarfs, um das Funktionieren der normalen physiologischen Vorgänge zu gewährleisten, sondern vielmehr darum, Stoffwechselwege auf zellulärer Ebene und somit die Anpassungsmechanismen an verschiedene Trainingsreize zu optimieren. Bei ihrem Abbau liefern die Makronährstoffe dem Organismus zum einen Verbrennungsenergie und zum anderen Bausteine, welche dann entweder zur Energiegewinnung weiter zerlegt (kataboler Stoffwechsel) oder zum Aufbau neuer Moleküle (anaboler Stoffwechsel) verwendet werden können. Bezüglich der Sporternährung können Nahrungsergänzungsmittel unter bestimmten Umständen dazu beitragen, die Deckung des Nährstoffbedarfs zu erleichtern bzw. optimieren.
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Aims: Green tea extract (GTE) can exert anti-obesity and inflammatory effects. Our study determined whether the benefits of GTE are summative with exercise-induced changes in anthropometric indices, and the levels of inflammatory cytokines, adiponectin and irisin in inactive overweight women. Methods: Thirty overweight female participants were randomized to three groups: endurance training + placebo (ET+P); endurance training + GTE (ET +GTE); and Control (no exercise) + placebo (Control, N=10). The exercise intervention consisted of an eight-week endurance-training program of three sessions per week [aerobics, aerobic circuit training, and fast walking or jogging at a moderate intensity of 40-59% of the heart rate reserve]. The dose of GTE used was 500 mg/d in the form of a green tea capsule. Results: Body weight, body mass index (BMI), waist to hip ratio (WHR), and body fat percentage (BFP) were decreased in both ET+P and ET+GTE interventions (P<0.001 for both interventions). The reduction of anthropometric values in the ET+GTE group was significantly higher than ET+P interventions (P<0.001). Both exercise interventions also significantly (P< 0.001) increased adiponectin [ET +GTE= 5.28 mg/ml (95% CI, 4.48 to 6.08) and ET+P= 3.34 mg/ml (95% CI, 2.76 to 3.92)] and decreased hs-CRP [ET +GTE= -0.95 mg/l (95% CI, -1.15 to -0.75) and ET+P= -0.35 mg/l (95% CI, -0.46 to -0.24)]. Changes in adiponectin and hs-CRP were greater (P< 0.05) in ET+GTE compared to ET+P. There were no significant differences in irisin, IL-6, and TNF-α between the three groups (P>0.05). Conclusions: GTE improves exercise-induced body composition by further decreasing exercise-induced changes in weight, BMI, WHR, and BFP. The combination of GTE and exercise also produced greater changes in anti-inflammatory (increases in adiponectin) and metabolic (decreases in hs-CRP) markers than exercise alone.
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Exercise training performed at the maximal fat oxidation intensity (FMT) stands out as a potential treatment of overweight and obesity. This work is a meta-analysis of randomized clinical trials of studies about the effect of FMT on fat mass and maximal oxygen consumption using PubMed, SCOPUS, EBSCOhost, and ScienceDirect as databases. Two independent reviewers selected 11 trials from 356 publications identified by the following keywords: fatmax, lipoxmax, maximal fat oxidation, peak of fat oxidation, physical training, physical exercise, body fat (BF), fat mass, overweight, and obesity. The risk of bias was assessed following the Cochrane Guidelines. The pooled mean difference was computed for each outcome with the random-effects model and the inverse-variance method. The meta-analysis was performed with the RevMan software v 5.3, and the heterogeneity across studies by the I2. The statistical significance was accepted at p < 0.05. Results showed that the FMT reduced body weight (MD = −4.30 kg, p < 0.01, I2 = 0%), fat mass (MD = −4.03 kg, p < 0.01, I2 = 0%), and waist circumference (MD = −3.34 cm, p < 0.01). Fat-free mass remains unchanged (MD = 0.08 kg, p = 0.85), but maximal oxygen consumption increased (MD = 2.96 mL∙kg−1∙min−1, p < 0.01, I2 = 0%). We conclude that FMT at short and medium-term (eight to twenty weeks) reduces body weight and BF, increasing cardiovascular fitness in low physical fitness people with obesity.
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Introducción: el efecto del ejercicio sobre la oxidación de los ácidos grasos depende de la intensidad y la duración. La ingesta de hidratos de carbono (HC) previo a una rutina de entrenamiento disminuye la tasa de oxidación de los ácidos grasos (FATmax). En contraste, el efecto del consumo de ácidos grasos monoinsaturados (AGMI) es poco concluyente. Objetivos: comparar el efecto de dos colaciones isocalóricas consumidas una hora antes de una sesión de ejercicio físico estandarizado durante nueve semanas sobre FATmax y la disminución de la masa grasa en adultos sanos físicamente activos. Metodología: ensayo clínico aleatorizado controlado. Un total de 19 sujetos entre 20 y 39 años fueron distribuidos al azar en tres grupos: grupo HC, con una colación alta en HC complejos; grupo lípidos, con una colación alta en AGMI; y grupo control, con ayuno mínimo de tres horas previo a la sesión de ejercicio. Se realizaron mediciones de FATmax, análisis de composición corporal y entrenamiento de resistencia aeróbica, con modalidades continuas e interválicas. Resultados: el grupo control mostró una tendencia a la disminución de masa grasa después de nueve semanas de entrenamiento. El FATmax fue mayor en los grupos HC y control en condiciones de pre y postintervención. Sin embargo, no se observaron diferencias significativas para FATmax entre los grupos. Conclusiones: el FATmax y la disminución de masa grasa podrían no estar influenciados por el tipo de alimentos previamente consumidos antes del ejercicio.
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Pulses (i.e., lentils, chickpeas, beans, peas) are low-glycemic index, high-fiber foods that are beneficial for improving blood lipids. Young soccer players typically have low dietary fiber intake, perhaps because of concerns regarding gastro-intestinal problems during exercise performance. Twenty-seven (17 females) soccer players were randomized to receive a pulse-based diet or their regular diet for four weeks in a cross-over study and evaluated for changes in blood lipids and athletic performance, with 19 (22 ± 6y; 12 females) completing the study (eight participants withdrew because of lack of time). Women increased high density lipoproteins (+0.5 ± 0.7 vs. −0.6 ± 0.3 mmol/L; p < 0.01) and reduced total cholesterol to high density lipoprotein ratio (−2.4 ± 2.9 vs. +2.6 ± 2.2; p < 0.01) on the pulse-based vs. regular diet, respectively, while there were no differences between diet phases in men. Athletic performance assessed by distance covered during games by a global positioning system was not significantly different during the pulse-based vs. regular diet (9180 ± 1618 vs. 8987 ± 1808 m per game; p = 0.35). It is concluded that a pulse-based diet can improve blood lipid profile without affecting athletic performance in soccer players.
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The aim of this study was to compare of different timing effect of carbohydrate intake before exercise on maximal fat oxidation (MFO) and Fatmax in endurance runners. Eight professional endurance runners (age 21.6±2.61 years, VO2max 63.0±8.7 ml.kg.min, body fat percentage 9.1±1.92, Background 7±3 years) participated as the subject in four separate trials. In the first session, the participants performed a graded exercise tests at 8 a.m. in fasted condition on treadmill to exhaustion in order to determine the amount of Fatmax and MFO. In the second, third and fourth session, with an interval of seven to ten days, participants in fasted condition, consumed 1 gr carbohydrate per kg body weight, with 500 ml water five minutes, one and three hours before the beginning of graded exercise tests. The amount of MFO and Fatmax were measured through indirect calorimetry method using the gas analysis system with aim of stoichiometric equation. The analysis of variance tests with repeated measures was used for data analysis. When carbohydrate is consumed five minutes and one hour prior to physical activity, MFO and Fatmax depict the lowest and highest decline respectively. MFO and Fatmax, in fasted condition, was significantly higher than the consumption of carbohydrate five minutes, one hour and three hours before the exercise (P<0.05). But no significant difference was seen in MFO and fatmax between different conditions of carbohydrate consumption. In general, the results indicated that consumption of carbohydrate in different timings before exercise cause the decrease in MFO and transferring of Fatmax to lower intensity of exercise. This means that the start of fat oxidation reduction occurs in lower intensity and participants depend more on carbohydrate sources.
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Introduction: The aim of this study was to compare maximal fat oxidation and the exercise intensity that elicit maximal fat oxidation (Fatmax) between active and inactive elderly men. Methods: 10 healthy elderly men that had regular exercise (at least 10 past years, VO2max 44.64±4.52 ml.kg.min) and 10 healthy elderly men that hadn’t any regular exercise (at least 10 past years, VO2max 30.92±3.25 ml.kg.min), were selected as the subjects of this study. Then, the participants performed an incremental exercise test at 8 to 10 am in the fasting state, including activity with 3 minutes stages on a treadmill to exhaustion. The amount of maximal fat oxidation and Fatmax were measured through the indirect calorimetry method using the gas analysis system with the aim of the stoichiometric equation. To compare the variables, the independent t-test (p>0.05) was used. Results: Fat oxidation rate in the range of intensities, maximal fat oxidation and Fatmax in active elderly men was significantly higher than inactive elderly men (p<0/05). But, the Carbohydrate oxidation rate in the range of intensities was significantly lower in the active compared to inactive elderly (p<0/05). Conclusion: In general, it was found that a better state of fitness in active elderly associated with higher fat oxidation and lower carbohydrate oxidation in the range of intensities. Moreover the amount of maximal fat oxidation and Fatmax decrease in the elderly, but this decrease can partly be prevented with regular exercise.
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Repeated periodization of carbohydrate (CHO) intake using a diet-exercise strategy called the sleep-low model can potentially induce mitochondrial biogenesis and improve endurance performance in endurance-trained individuals. However, more studies are needed to confirm the performance-related effects and to investigate the sustained effects on maximal fat oxidation (MFO) rate and proteins involved in intramuscular lipid metabolism. Thirteen endurance-trained males (age 23-44 years; V ˙ O2 -max, 63.9 ± 4.6 mL·kg-1 ·min-1 ) were randomized into two groups: sleep-low (LOW-CHO) or high CHO availability (HIGH-CHO) in three weekly training blocks over 4 weeks. The acute metabolic response was investigated during 60 minutes of exercise within the last 3 weeks of the intervention. Pre- and post-intervention, 30-minute time-trial performance was investigated after a 90-minute pre-load, which as a novel approach included nine intense intervals (and estimation of MFO). Additionally, muscle biopsies (v. lateralis) were obtained to investigate expression of proteins involved in intramuscular lipid metabolism using Western blotting. During acute exercise, average fat oxidation rate was ~36% higher in LOW-CHO compared to HIGH-CHO (P = .03). This did not translate into sustained effects on MFO. Time-trial performance increased equally in both groups (overall time effect: P = .005). We observed no effect on intramuscular proteins involved in lipolysis (ATGL, G0S2, CGI-58, HSL) or fatty acid transport and β-oxidation (CD-36 and HAD, respectively). In conclusion, the sleep-low model did not induce sustained effects on MFO, endurance performance, or proteins involved in intramuscular lipid metabolism when compared to HIGH-CHO. Our study therefore questions the transferability of acute effects of the sleep-low model to superior sustained adaptations.
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New findings: What is the central question of this study? Females rely to a greater extent than males on fat oxidation during exercise. Whether any difference in skeletal muscle mitochondrial phenotype and oxidative capacity contributes to this sexual dimorphism remains incompletely explored. What is the main finding and its importance? Female prioritization of fat during exercise occurs in parallel to augmented mitochondrial volume density and intrinsic fatty acid and lactate oxidation in skeletal muscle fibres compared with males, independently of aerobic exercise capacity. The enlarged metabolic machinery in skeletal muscle of females is associated with lower body size and leg mass. Abstract: Fat oxidation during exercise is greater in females than in males. We sought to determine whether sex differences in substrate metabolism are paralleled by distinct skeletal muscle mitochondrial volume density and oxidative capacity. Whole-body substrate (fat and carbohydrate) utilization during submaximal treadmill running was assessed, and skeletal muscle biopsies were taken to determine mitochondrial volume density and function in healthy young females (n = 12) and males (n = 12) matched by aerobic exercise capacity and exercise performance. Females presented a lower respiratory exchange ratio (0.87 ± 0.04 versus 0.91 ± 0.04, P = 0.023) and whole-body carbohydrate oxidation (27.8 ± 8.3 versus 35.8 ± 6.5 mg kg-1 min-1 , P = 0.027), whereas fat oxidation was higher (8.7 ± 2.8 versus 5.9 ± 2.6 mg kg-1 min-1 , P = 0.034) during submaximal exercise compared with males. In skeletal muscle biopsies, females demonstrated augmented mitochondrial volume density (7.51 ± 1.77 versus 5.90 ± 1.72%, P = 0.035) and oxidative capacity for fatty acid [36.6 ± 12.8 versus 24.5 ± 7.3 pmol O2 s-1 (mg wet weight)-1 , P = 0.009] and lactate [71.1 ± 24.4 versus 53.2 ± 14.6 pmol O2 s-1 (mg wet weight)-1 , P = 0.040]. No sex differences in respiratory exchange ratio, whole-body fat oxidation and skeletal muscle variables were detected when adjusted for anthropometric variables including body mass or leg mass, which were lower in females. In conclusion, female prioritization of fat over carbohydrate oxidation during exercise is underpinned by augmented body size-related mitochondrial volume density, fatty acid and lactate oxidative capacity in skeletal muscle fibres.
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Anthocyanin supplements are receiving attention due to purported benefits to physiological, metabolic, and exercise responses in trained individuals. However, the efficacy of anthocyanin intake over multiple testing days is not known. We compared a placebo and two doses of anthocyanin-rich New Zealand blackcurrant (NZBC) extract (300 and 600 mg·day−1) on plasma lactate, substrate oxidation, and 16.1 km time trial (TT) performance on three occasions over 7-days in a fed state (day 1 (D1), D4, and D7). Thirteen male cyclists participated in a randomized, crossover, placebo-controlled double-blind design. There was no difference in plasma lactate and substrate oxidation between conditions and between days. A time difference was observed between D1 (1701 ± 163 s) and D4 (1682 ± 162 s) for 600 mg (p = 0.05), with an increment in average speed (D1 = 34.3 ± 3.4 vs. D4 = 34.8 ± 3.4 km·h−1, p = 0.04). However, there was no difference between the other days and between conditions. Overall, one week of intake of NZBC extract did not affect physiological and metabolic responses. Intake of 600 mg of NZBC extract showed inconsistent benefits in improving 16.1 km time trial performance over a week period in trained fed cyclists.
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Purpose: Ingesting readily oxidized carbohydrates (CHO) such as sucrose during exercise can improve endurance performance. Whether lactose can be utilized as a fuel source during exercise is unknown. The purpose of this study was to investigate the metabolic response to lactose ingestion during exercise, compared to sucrose or water. Methods: 11 participants (age, 22 ± 4 years; V[Combining Dot Above]O2peak, 50.9 ± 4.7 ml·min·kg) cycled at 50% Wmax for 150 min on 5 occasions. Participants ingested CHO beverages (lactose or sucrose; 48 g·h, 0.8 gmin) or water throughout exercise. Total substrate and exogenous CHO oxidation was estimated using indirect calorimetry and stable isotope techniques (naturally high C-abundance CHO ingestion). Naturally low C-abundance CHO trials were conducted to correct background shifts in breath CO2 production. Venous blood samples were taken to determine plasma glucose, lactate and non-esterified fatty acids (NEFA) concentrations. Results: Mean exogenous CHO oxidation rates were comparable with lactose (0.56 ± 0.19 g·min) and sucrose (0.61 ± 0.10 g·min; P=0.49) ingestion. Endogenous CHO oxidation contributed less to energy expenditure in Lactose (38 ± 14 %) versus Water (50 ± 11 %, P=0.01) and Sucrose (50 ± 7 %, P≤0.05). Fat oxidation was higher in Lactose (42 ± 8 %) than Sucrose (28 ± 6 %, P≤0.01); CHO conditions were lower than Water (50 ± 11 %; P≤0.05). Plasma glucose was higher in Lactose and Sucrose than Water (P≤0.01); plasma lactate was higher in Sucrose than Water (P≤0.01); plasma NEFA were higher in Water than Sucrose (P≤0.01). Conclusions: Lactose and sucrose exhibited similar exogenous CHO oxidation rates during exercise at moderate ingestion rates. Compared to sucrose ingestion, lactose resulted in higher fat and lower endogenous CHO oxidation.
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It has been suggested that glycogen functions not only in carbohydrate energy storage, but also as molecular sensors capable of activating lipolysis. This study aimed to compare the variation in liver and muscle glycogen during the day due to different timing of exercise. Nine healthy young men participated in two trials in which they performed a single bout of exercise at 70% of their individual maximal oxygen uptake for 60 min in the post-absorptive (morning) or post-prandial (afternoon) state. Liver and muscles glycogen levels were measured using carbon magnetic resonance spectroscopy ( ¹³ C MRS). Diurnal variations in liver and muscle glycogen compared to baseline levels were significantly different depending on the timing of exercise. The effect of the timing of exercise on glycogen fluctuation is known to be related to a variety of metabolic signals, and the results of this study will be useful for future research on energy metabolism.
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Seven men were studied during 30 min of treadmill exercise (approximately 70% VO2 max) to determine the effects of increased availability of plasma free fatty acids (FFA) and elevated plasma insulin on the utilization of muscle glycogen. This elevation of plasma FFA (1.01 mmol/1) with heparin (2,000 units) decreased the rate of muscle glycogen depletion by 40% as compared to the control experiment (FFA = 0.21 mmol/1). The ingestion of 75 g of glucose 45 min before exercise produced a 3.3-fold increase in plasma insulin and a 38% rise in plasma glucose at 0 min of exercise. Subsequent exercise increased muscle glycogen utilization and total carbohydrate (CHO) oxidation 17 and 13%, respectively, when compared to the control trial. This elevation of plasma insulin produced hypoglycemia (less than 3.5 mmol/1) in most subjects throughout the exercise. These data illustrate the regulatory influence of both plasma insulin and FFA on the rate of CHO usage during prolonged severe muscular activity.
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We have investigated the role of triglyceride-fatty acid cycling in amplifying control of the net flux of fatty acids in response to exercise and in recovery from exercise. Five normal volunteers were infused with [1-13C]palmitate and D-5-glycerol throughout rest, 4 h of treadmill exercise at 40% maximum O2 consumption, and 2 h of recovery. Total fat oxidation was quantified by indirect calorimetry. Lipolysis (rate of appearance of glycerol) increased from 2.1 +/- 0.3 to 6.0 +/- 1.2 mumol.kg-1.min-1 after 30 min of exercise and progressively increased thereafter to a value of 10.5 +/- 0.8 mumol.kg-1.min-1 after 4 h. Lipolysis decreased rapidly during the first 20 min of recovery, but it was still significantly elevated after 2 h of recovery. The rate of appearance of free fatty acids followed the same pattern of response. Seventy percent of released fatty acids were reesterified at rest, and this value decreased to 25% within the first 30 min of exercise. Reesterification remained less than 35% of lipolysis until the start of recovery, at which time the value rose to 90%. In exercise, more than one-half the increase in fat oxidation could be attributed to the reduction in the percent reesterification. Most of the change in percent reesterification during exercise and recovery was caused by changes in extracellular cycling of fatty acids released into plasma. We conclude that triglyceride-fatty acid cycling plays an important role in enabling a rapid response of fatty acid metabolism to major changes in energy metabolism.
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Lipoprotein lipase (LPL) catalyzes the flux-generating step in transport of fatty acids from lipoprotein triacylglycerols into tissues for use in metabolic reactions. In vitro studies have shown that fatty acids can bind to the enzyme and impede its other interactions. In this study we have searched for evidence of fatty acid control of LPL in vivo by rapid infusion of a triacylglycerol emulsion to healthy volunteers. During infusion the activity of LPL but not of hepatic lipase increased in plasma, but to different degrees in different individuals. The time course for the increase in LPL activity differed from that for triacylglycerols but followed the plasma levels of free fatty acids. This was true during infusions and when the emulsion was given as a bolus injection. In particular there were several instances when plasma triacylglycerol levels were very high but free fatty acids and LPL activity remained low. Model studies with bovine LPL showed that fatty acids displace the enzyme from heparin-agarose. We suggest that in situations when fatty acids are generated more rapidly by LPL than they are used by the local tissue, they cause dissociation of the enzyme from its binding to endothelial heparin sulfate and are themselves released into circulation.
Article
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Six men were studied to compare the effects of pre-exercise carbohydrate feedings on endurance performance and muscle glycogen utilization during prolonged exercise. Trials consisted of a cycling ride to exhaustion at 75% maximal oxygen uptake preceded by the ingestion of either 75 g of glucose in 350 ml of water (GLU), 75 g of fructose in 350 ml of water (FRU), or 350 ml of an artificially sweetened and flavored placebo (CON). No differences were observed between trials for oxygen uptake, respiratory exchange ratio, heart rate, or exercise time to exhaustion (CON = 92.7 +/- 5.2 min, FRU = 90.6 +/- 12.4, and GLU = 92.8 +/- 11.3, mean +/- SE). Blood glucose was elevated as a result of the GLU feeding, but fell rapidly with the onset of exercise, reaching a low of 4.02 +/- 0.34 mmol X l-1 at 15 min of exercise. Serum insulin also increased following the GLU feeding but had returned to pre-drink levels by 30 min of exercise. No differences in blood glucose and insulin were observed between FRU and CON. Muscle glycogen utilization during the first 30 min of exercise (CON = 46.3 +/- 8.2 mmol X kg-1 wet weight, FRU = 56.3 +/- 3.0 mmol X kg-1 wet weight, GLU = 50.0 +/- 4.9 mmol X kg-1 wet weight) and total glycogen use (CON = 93.4 +/- 11.1, FRU = 118.8 +/- 10.9, and GLU = 99.5 +/- 4.3) were similar in the three trials.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
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Stable isotope tracers and indirect calorimetry were used to evaluate the regulation of endogenous fat and glucose metabolism in relation to exercise intensity and duration. Five trained subjects were studied during exercise intensities of 25, 65, and 85% of maximal oxygen consumption (VO2max). Plasma glucose tissue uptake and muscle glycogen oxidation increased in relation to exercise intensity. In contrast, peripheral lipolysis was stimulated maximally at the lowest exercise intensity, and fatty acid release into plasma decreased with increasing exercise intensity. Muscle triglyceride lipolysis was stimulated only at higher intensities. During 2 h of exercise at 65% VO2max plasma-derived substrate oxidation progressively increased over time, whereas muscle glycogen and triglyceride oxidation decreased. In recovery from high-intensity exercise, although the rate of lipolysis immediately decreased, the rate of release of fatty acids into plasma increased, indicating release of fatty acids from previously hydrolyzed triglycerides. We conclude that, whereas carbohydrate availability is regulated directly in relation to exercise intensity, the regulation of lipid metabolism seems to be more complex.
Article
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Six male subjects received either a saline (control) or Intralipid infusion during 30 min rest and 15 min cycling at 85% maximal O2 uptake (VO2max) to examine the regulation of fat-carbohydrate interaction (glucose-fatty acid cycle) in skeletal muscle. Muscle biopsies were sampled immediately before and at 3 and 15 min of exercise in both trials. A muscle biopsy was also taken at -30 min rest in the Intralipid trial. Intralipid infusion significantly elevated plasma free fatty acids above control during rest (0.21 +/- 0.04 to 0.94 +/- 0.09 mM) and exercise (5 min: 1.27 +/- 0.15 mM; 15 min: 1.42 +/- 0.13 mM). Muscle glycogen degradation was significantly lower in the Intralipid trial (109.7 +/- 29.3 vs. 194.7 +/- 32.1 mmol/kg dry muscle). Muscle lactate accumulation after 15 min was similar in both trials (control, 60.7 +/- 12.2 and Intralipid, 60.9 +/- 12.4 mmol/kg dry muscle). Muscle citrate increased at rest during Intralipid (0.32 +/- 0.06 to 0.58 +/- 0.06 mmol/kg dry muscle) but was not different between trials at 3 min (control, 0.73 +/- 0.07 and Intralipid, 0.68 +/- 0.06 mmol/kg dry muscle) and 15 min of cycling. Resting acetyl-CoA was unaffected by Intralipid and increased similarly in both trials at 3 min of cycling (control, 59.0 +/- 10.3 and Intralipid, 50.7 +/- 13.6 mumol/kg dry muscle) and remained unchanged at 15 min. Pyruvate dehydrogenase activity increased five- to sevenfold during exercise and was similar in both trials (15 min: control, 2.42 +/- 0.30 and Intralipid, 2.79 +/- 0.41 mmol.min-1 x kg wet wt-1).(ABSTRACT TRUNCATED AT 250 WORDS)
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This study examined muscle glycogenolysis and the regulation of glycogen phosphorylase (Phos) activity during 15 min of cycling at 85% of maximal O2 consumption (VO2max) in control and high free fatty acid (FFA; Intralipid-heparin) conditions in 11 subjects. Muscle biopsies were sampled at rest and 1, 5, and 15 min of exercise, and glycogen Phos transformation state (%Phos alpha), substrate (Pi, glycogen), and allosteric regulator (ADP, AMP, IMP) contents were measured. Infusion of intralipid elevated plasma FFA from 0.32 +/- 0.04 mM at rest to 1.00 +/- 0.04 mM just before exercise and 1.12 +/- 0.10 mM at 14 min of exercise. In the control trial, plasma FFA were 0.36 +/- 0.04 mM at rest and unchanged at the end of exercise (0.34 +/- 0.03 mM). Seven subjects used less muscle glycogen (46.7 +/- 7.6%, mean +/- SE) during the Intralipid trial, and four did not respond. In subjects who spared glycogen, glycogen Phos transformation into the active (alpha) form was unaffected by high FFA except for a nonsignificant reduction during the initial 5 min of exercise. Total AMP and IMP contents were not significantly different during exercise between trials, but total ADP was significantly lower with Intralipid only at 15 min. The calculated free ADP, AMP, and Pi contents were lower with Intralipid but not significantly different. However, when the present results were pooled with the data from a previous study using the same protocol [Dyck et al., Am. J. Physiol. 265 (Endocrinol, Metab. 28): E852-E859, 1993], the free ADP, AMP, and Pi contents of all subjects who spared glycogen (n = 13) were significantly lower at 15 min in the Intralipid trial. The findings suggest that the elevation of plasma FFA during intense cycling spares muscle glycogen by posttransformational regulation of Phos. This may be due to blunted increases in the contents of AMP, an allosteric activator of Phos alpha, and Pi, a substrate for Phos.
Article
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To evaluate the extent to which decreased plasma free fatty acid (FFA) concentration contributes to the relatively low rates of fat oxidation during high-intensity exercise, we studied FFA metabolism in six endurance-trained cyclists during 20-30 min of exercise [85% of maximal O2 uptake (VO2max)]. They were studied on two occasions: once during a control trial when plasma FFA concentration is normally low and again when plasma FFA concentration was maintained between 1 and 2 mM by intravenous infusion of lipid (Intralipid) and heparin. During the 20-30 min of exercise, fat and carbohydrate oxidation were measured by indirect calorimetry, and the rates of appearance (Ra) of plasma FFA and glucose were determined by the constant infusion of [6,6-2H2]glucose and [2H2]palmitate. Lipid-heparin infusion did not influence the Ra or rate of disappearance of glucose. During exercise in the control trial, Ra FFA failed to increase above resting levels (11.0 +/- 1.2 and 12.4 +/- 1.7 mumol.kg-1.min-1 for rest and exercise, respectively) and plasma FFA concentration dropped from a resting value of 0.53 +/- 0.08 to 0.29 +/- 0.02 mM. The restoration of plasma FFA concentration resulted in a 27% increase in total fat oxidation (26.7 +/- 2.6 vs. 34.0 +/- 4.4 mumol.kg-1.min-1, P < 0.05) with a concomitant reduction in carbohydrate oxidation, apparently due to a 15% (P < 0.05) reduction in muscle glycogen utilization. However, the elevation of plasma FFA concentration during exercise at 85% VO2max only partially restored fat oxidation compared with the levels observed during exercise at 65% VO2max. These findings indicate that fat oxidation is normally impaired during exercise at 85% VO2max because of the failure of FFA mobilization to increase above resting levels, but this explains only part of the decline in fat oxidation when exercise intensity is increased from 65 to 85% VO2max.
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Previously described colorimetric ultramicro methods for the determination of serum and tissue fatty acids have been improved in sensitivity and selectivity by extracting cobalt rather than copper soaps by means of a solvent lighter than water instead of chloroform. The complex of Co⁺⁺ with α-nitroso-Β-naphthol is measured at 500 mμ.
Chapter
Triglycerides with the phosphatides, and the free and esterified cholesterol, make up the quantitatively most important lipid fractions of blood. Adipose tissue has the highest triglyceride content, between 60 and 85 %. The measurements of neutral fat by the determination of glycerol by chemical or fluorimetric methods require extraction and careful isolation of triglycerides followed by hydrolysis. In the enzymatic determination of triglycerides in blood serum or plasma, the isolation or purification of the triglycerides or the extraction of fat can be omitted. The glycerol present in serum, plasma, or Folch extracts of tissues before and after ethanolic-alkaline hydrolysis is converted to glycerophosphate and adenosine diphosphate (ADP) with ATPand glycerokinase. The ADP reacts with pyruvate kinase and added phosphoenolpyruvate to give that is reduced to lactate with NADH and lactate dehydrogenase.
Article
Six men performed two-legged cycle ergometer exercise at loads demanding 2–4 and 3–4 litres O2 min-1 (62 and 84% of Vo2 max) for 20 min each or to exhaustion twice with 1 h rest between. An initial glycogen difference of 28 mmol glucose units kg-1 of thigh muscle between the two legs was produced by one-legged exercise on a previous day followed by the consumption of a low carbohydrate diet. During the 1 h rest nicotinic acid (NA) was administered to inhibit lipolysis. Total body Fo2 was unchanged by the NA administration. Work done by each leg, indicated by force on the pedals, was equal. RQ indicated a larger oxidation of fat in the leg with low glycogen. Muscle glycogen was 15 and 10 mmol kg-1 in the normal and low glycogen leg at the end of the first exercise bouts and 3–8 mmol kg-1 in both legs at exhaustion. The low glycogen leg extracted lactate from the blood whereas the normal leg released lactate and the uptake of glucose from the blood was greater by the low glycogen leg. These differences between the low glycogen and control legs did not persist during the NA condition when muscle glycogen content was equal in both legs. Further, the leg glucose uptake in the control and the NA conditions was positively related to the percentage of glycogen-empty muscle fibres and inversely to the glucose-6-P04 concentration. Thus the magnitude of the local glycogen stores of muscle influences the uptake and use of blood-borne substrates as well as determining endurance capacity during moderate to high intensity exercise.
Article
The regulation of lipolysis, free fatty acid appearance into plasma (FFA R(a)), an FFA reesterification and oxidation were examined in seven healthy humans infused intravenously with insulin at rates of 4, 8, 25, and 400 mU.m-2.min-1. Glycerol and FFA R(a) were determined by isotope dilution methods, and FFA oxidation was calculated by indirect calorimetry or by measurement of expired 14CO2 from infused [1-14C]palmitate. These measurements were used to calculate total FFA reesterification, primary FFA reesterification occurring within the adipocyte, and secondary reesterification of circulating FFA molecules. Lipolysis, FFA R(a), and secondary FFA reesterification were exquisitely insulin sensitive [the insulin concentrations that produced half-maximal suppression (EC50), 106 +/- 26, 91 +/- 20 vs. 80 +/- 16 pM, P = not significant] in contrast to insulin suppression of FFA oxidation (EC50, 324 +/- 60, all P < 0.01). The absolute rate of primary FFA reesterification was not affected by the increase in insulin concentration, but the proportion of FFA molecules undergoing primary reesterification doubled over the physiological portion of the insulin dose-response curve (from 0.23 +/- 0.06 to 0.44 +/- 0.07, P < 0.05). This served to magnify insulin suppression of FFA R(a) twofold. In conclusion, insulin regulates FFA R(a) by inhibition of lipolysis while maintaining a constant rate of primary FFA reesterification.
Article
To determine how long a meal will affect the metabolic response to exercise, nine endurance-trained and nine untrained subjects cycled for 30 min at 70% of peak O2 consumption (VO2 peak) 2, 4, 6, 8, and 12 h after eating 2 g carbohydrate/kg body wt. In addition, each subject completed 30 min of cycling 4 h after the meal at an intensity that elicited a respiratory exchange ratio (RER) of 0.94-0.95. During exercise after 2 and 4 h of fasting, carbohydrate oxidation was elevated 13-15% compared with the response to exercise after an 8- and 12-h fast (P less than 0.01). The increase in blood glycerol concentration during exercise (30 to 0 min) was linearly related to the length of fasting (r = 0.99; P less than 0.01). In all subjects, plasma glucose concentration declined 17-21% during exercise after 2 h of fasting (P less than 0.01). Plasma glucose concentration also declined (15-25%) during exercise in the trained subjects after 4 and 6 h of fasting (P less than 0.05) but did not change in the untrained subjects. However, the decline in plasma glucose concentration was similar (14%) in the two groups when the exercise intensity was increased in the trained subjects (i.e., 78 +/- 1% VO2 peak) and decreased in the untrained subjects (i.e., 65 +/- 3% VO2 peak) to elicit a similar RER.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
To assess the effects of endurance training on plasma glucose kinetics during moderate-intensity exercise in men, seven men were studied before and after 12 wk of strenuous exercise training (3 days/wk running, 3 days/wk cycling). After priming of the glucose and bicarbonate pools, [U-13C] glucose was infused continuously during 2 h of cycle ergometer exercise at 60% of pretraining peak O2 uptake (VO2) to determine glucose turnover and oxidation. Training increased cycle ergometer peak VO2 by 23% and decreased the respiratory exchange ratio during the final 30 min of exercise from 0.89 +/- 0.01 to 0.85 +/- 0.01 (SE) (P less than 0.001). Plasma glucose turnover during exercise decreased from 44.6 +/- 3.5 mumol.kg fat-free mass (FFM)-1.min-1 before training to 31.5 +/- 4.3 after training (P less than 0.001), whereas plasma glucose clearance (i.e., rate of disappearance/plasma glucose concentration) fell from 9.5 +/- 0.6 to 6.4 +/- 0.8 ml.kg FFM-1.min-1 (P less than 0.001). Oxidation of plasma-derived glucose, which accounted for approximately 90% of plasma glucose disappearance in both the untrained and trained states, decreased from 41.1 +/- 3.4 mumol.kg FFM-1.min-1 before training to 27.7 +/- 4.8 after training (P less than 0.001). This decrease could account for roughly one-half of the total reduction in the amount of carbohydrate utilized during the final 30 min of exercise in the trained compared with the untrained state.
Article
Methodology for measuring plasma free fatty acid (FFA) turnover/oxidation with [1-14C]palmitate was tested in normal subjects. In study 1, two different approaches (720-min tracer infusion without prime vs. 150-min infusion with NaH14CO3 prime) to achieve steady-state conditions of 14CO2 yielded equivalent rates of plasma FFA turnover/oxidation. In study 2, during staircase NaH14CO3 infusion, calculated rates of 14CO2 appearance agreed closely with NaH14CO3 infusion rates. In study 3, 300-min euglycemic insulin clamp documented that full biological effect of insulin on plasma FFA turnover/oxidation was established within 60-120 min. In study 4, plasma insulin concentration was raised to 14 +/- 2, 23 +/- 2, 38 +/- 2, 72 +/- 5, and 215 +/- 10 microU/ml. A dose-dependent insulin suppression of plasma FFA turnover/oxidation was observed. Plasma FFA concentration correlated positively with plasma FFA turnover/oxidation in basal and insulinized states. Total lipid oxidation (indirect calorimetry) was significantly higher than plasma FFA oxidation in the basal state, suggesting that intracellular lipid stores contributed to whole body lipid oxidation. Hepatic glucose production and total glucose disposal showed the expected dose-dependent suppression and stimulation, respectively, by insulin. In conclusion, insulin regulation of plasma FFA turnover/oxidation is maximally manifest at low physiological plasma insulin concentrations, and in the basal state a significant contribution to whole body lipid oxidation originates from lipid pool(s) that are different from plasma FFA.
Article
The effect on exercising muscle metabolism of prior ingestion of 200 g glucose was examined in six healthy subjects during 40 min leg exercise at 30% of maximal oxygen uptake. Leg glucose uptake during exercise was on average two- to three-fold higher after glucose (E + G) compared to exercise without glucose (E) and could account for 44-48% of the oxidative leg metabolism (control value: 19%, P less than 0.05-0.01). In contrast to E, which was associated with a significant release of leg lactate, pyruvate and alanine, E + G gave no leg production of lactate or alanine and an uptake of pyruvate. The respiratory exchange ratios (R) were higher during G + E and corresponded to a carbohydrate oxidation of 54-69% as against 46-49% (P less than 0.05-0.01) during E. Estimated from R-values and leg oxygen and glucose uptakes, carbohydrate oxidation during G less than E was almost completely accounted for by blood glucose. During E, on the other hand, carbohydrate oxidation exceeded leg glucose uptake, indicating a small but significant muscle glycogen breakdown (P less than 0.01). The rate of glycogen utilization during E or G + E was too small to be detected by direct measurements of muscle glycogen content. The results demonstrate that glucose ingestion prior to light exercise is followed by increased uptake and more efficient oxidation of glucose, as well as by insignificant muscle glycogen degradation by exercising muscle. Although the present findings suggest a glycogen-conserving effect of glucose ingestion under these conditions, the main fuel shift is from fat to glucose oxidation.
Article
1. Glycerol kinase (EC 2.7.1.30) activity was measured in crude extracts of skeletal muscles by a radiochemical method. The properties of the enzyme from a number of different muscles are very similar to those of the enzyme from rat liver. Glycerol kinase from locust flight muscle was inhibited competitively by l-3-glycerophosphate with a K(i) of 4.0x10(-4)m. 2. The activity of glycerol kinase was measured in a variety of muscles from vertebrates and invertebrates in an attempt to explain the large variation in the activity of this enzyme in different muscles. 3. In vertebrates glycerol kinase activities were generally higher in red muscle than in white muscle; the highest activities (approx. 0.2mumole/min./g. fresh wt.) were found in the red breast muscle of some birds (e.g. pigeon, duck, blue tit) whereas the activities in the white breast muscle of the pheasant and domestic fowl were very low (approx. 0.02mumole/min./g.). 4. On the basis of glycerol kinase activities, muscles from insects can be classified into three groups: muscles that have a low enzyme activity, i.e. <0.3mumole/min./g. (leg muscles of all insects studied and the flight muscles of cockroaches and the tsetse fly); muscles that have an intermediate enzyme activity, i.e. 0.3-1.5mumoles/min./g. (e.g. locusts, cockchafers, moths, water-bugs); and muscles that have a high enzyme activity, i.e. >1.5mumoles/min./g. (e.g. bees, wasps, some blowflies). 5. The function of glycerol kinase in vertebrate and insect muscles that possess a low or intermediate activity is considered to be the removal of glycerol that is produced from lipolysis of triglyceride or diglyceride by the muscle. Therefore in these muscles the activity of glycerol kinase is related to the metabolism of fat, which is used to support sustained muscular activity. A possible regulatory role of glycerol kinase in the initiation of triglyceride or diglyceride lipolysis is discussed. 6. The function of glycerol kinase in the insect muscles that possess a high activity of the enzyme is considered to be related to the high rates of glycolysis that these muscles can perform. The oxidation of extramitochondrial NADH, and therefore the maintenance of glycolysis, is dependent on the functioning of the glycerophosphate cycle; if at any stage of flight (e.g. at the start) the rate of mitochondrial oxidation of l-3-glycerophosphate was less than the activity of the extramitochondrial glycerophosphate dehydrogenase, this compound would accumulate, inhibit the latter enzyme and inhibit glycolysis. It is suggested that such excessive accumulation of l-3-glycerophosphate is prevented by hydrolysis of this compound to glycerol; the latter would have to be removed from the muscle when the accumulation of l-3-glycerophosphate had stopped, and this would explain the presence of glycerol kinase in these muscles and its inhibition by l-3-glycerophosphate.
Article
To estimate "true" rate of glucose production, as well as glucose carbon recycling in humans, a mass spectrometric method with [U-13C]glucose as tracer was developed. Because the opportunity for the uniformly labeled glucose, [13C6]glucose, to recycle back as [13C6]glucose is negligible, the true glucose production rate was obtained by measuring the plasma isotope enrichment of [13C6]glucose with chemical ionization mass spectrometry. In contrast, when the isotopic enrichment of C-1 of glucose was measured by enzymatic decarboxylation and ratio mass spectrometry, the "apparent" glucose production including carbon recycling was obtained. The difference between the two rates was the extent of glucose carbon recycling. [U-13C]glucose was administered as primed constant-rate infusion to six normal healthy adult subjects. Rates of glucose turnover were calculated from tracer dilution by applying steady-state kinetics. The true rate of glucose production estimated by the present method was 2.02 +/- 0.19 mg X kg-1 X min-1 (mean +/- SD). After an overnight fast, glucose carbon recycling contributed from 3 to 26% of the total glucose production rate. Use of stable isotopes and mass spectrometric technique permits estimation of important parameters of glucose metabolism without resorting to multiple tracers and at the same time preventing the risk of radiation.
Article
The effect of a bout of exercise on glucose uptake and glycogen synthesis in skeletal muscle was examined using a perfused rat hindlimb preparation. Rats were subjected to a bout of swimming. The exercise stress was moderate as reflected in a reduction of muscle glycogen concentration of only 50%. Glucose uptake and glycogen synthesis were measured in perfused hindlimb muscles for a 30-min period beginning approximately 60 min following the exercise. The rate of glucose uptake in the absence of insulin was 10-fold higher in hindlimbs of exercised animals than in the controls. The rate of glucose uptake was also higher in exercised than in control muscles in the presence of 50 microunits/ml or 10 mU/ml of insulin, but these differences were smaller than that found in the absence of insulin. Conversion to glycogen was the major pathway for disposal of the glucose taken up by muscle. The rate of glycogen accumulation in the exercised plantaris muscles was greater than in the control muscles both in the absence and presence of insulin.
Article
1. The effect of infusion of noradrenaline (0.42 μmol min−1 kg−1) on the exchange of non-esterified fatty acids, glycerol and other metabolites across subcutaneous abdominal adipose tissue was investigated in five healthy subjects using an arteriovenous catheterization technique and measurement of adipose tissue blood flow using the 133Xe clearance technique. At the same time, the net rate of fat oxidation in the whole body was assessed by indirect calorimetry, and the turnover of glycerol in the whole body and in subcutaneous adipose tissue was estimated using [5-2H]glycerol, which was administered as a primed constant infusion for 1 h before (basal turnover) noradrenaline administration and continued during the 1 h of noradrenaline infusion. 2. The noradrenaline infusion increased the plasma noradrenaline concentration from a basal value of 0.9 ± 0.1 to 12.6 ± 1.2 nmol/(mean ± SEM) at 60 min. It also increased the arterialized concentration of glycerol by 50% (basal value 81 ± 11/μmol/l−1) and that of plasma non-esterified fatty acids three-fold (basal value 357 ± 86 μmol/l). 3. Noradrenaline increased the net release of glycerol by adipose tissue three-fold and that of non-esterified fatty acids three- to four-fold. Although the ratio of non-esterified fatty acid to glycerol release by adipose tissue increased in all subjects from a mean value of 2.7 in the basal period to 3.6 and 3.9 at 50 and 60 min of the noradrenaline infusion, respectively (P < 0.02), at no time point did the ratio differ significantly from 3.0 4. Noradrenaline increased the estimated rate of appearance of glycerol in the whole body from a basal value of 1.5 ± 0.3 to 2.6 ± 0.3 μmol min−1 kg−1 body weight, and the net rate of triacylglycerol oxidation from 1.2 ± 0.1 to 1.7 ± 0.13 μmol min−1 kg−1. The enrichment of glycerol in venous blood draining adipose tissue was two-fold lower than that predicted from the net addition of glycerol to the blood in the basal period (P < 0.02). 5. This study provides a direct demonstration of a ‘hormone’ stimulating lipolysis in human adipose tissue in viva The effect of noradrenaline in significantly increasing the ratio of non-esterified fatty acid to glycerol release by adipose tissue may be partly explained by accumulation in adipose tissue of diacylglycerol, which is associated with release of non-esterified fatty acids but not glycerol. Finally, since the low enrichment of glycerol in venous blood draining adipose tissue cannot be entirely explained by the net addition of glycerol in adipose tissue, there must be exchange between enriched glycerol in blood and unenriched glycerol in adipose tissue. This raises questions about the accuracy of glycerol turnover studies, which are typically carried out over 1 h.
Article
To examine whether hyperglycemia is an independent regulator of adipose tissue lipolysis, we measured palmitate flux ([3H]palmitate) on two occasions in eight volunteers with insulin-dependent diabetes. On one. occasion, euglycemia was maintained for 4 h continuously; on a different occasion, hyperglycemia (plasma glucose, 12 mmol/l) was induced after 2 h of euglycemia. Palmitate flux decreased from 1.39 +/- 0.22 to 1.25 +/- 0.18 mumol.kg-1 x min-1 during sustained euglycemia and from 1.43 +/- 0.24 to 1.13 +/- 0.19 mumol.kg-1 x min-1 during the transition from the euglycemic to the hyperglycemic study intervals. There were no significant differences between the changes in palmitate flux from the first to the second study interval on the control (euglycemia-euglycemia) and experimental (euglycemia-hyperglycemia) study days and no difference between palmitate flux on different study days. Thus, in the face of euinsulinemia, euglucagonemia, and the absence of somatostatin, no effect of hyperglycemia on free fatty acid metabolism could be detected in humans.
Article
To determine the metabolic effects of a single bout of exercise performed after a meal or in the fasting state, nine healthy subjects were studied over two 8-h periods during which net substrate oxidation was monitored by indirect calorimetry. On one occasion, exercise was performed 90 min after ingestion of a meal labeled with [U-13C]glucose [protocol meal-exercise (M-E)]. On the second occasion, exercise was performed after an overnight fast and was followed 30 min later by ingestion of an identical meal [protocol exercise-meal (E-M)]. Energy balances were similar in both protocols, but carbohydrate balance was positive (42.2 +/- 5.1 g), and lipid balance was negative (-11.1 +/- 2.0) during E-M, whereas they were nearly even during M-E. Total glycogen synthesis was calculated as carbohydrate intake minus oxidation of exogenous 13C-labeled carbohydrate (calculated from 13CO2 production). Total glycogen synthesis was increased by 90% (from 47.6 +/- 3.8 to 90.7 +/- 5.4 g, P < 0.0001) during E-M vs. M-E. Endogenous glycogen breakdown was calculated as net carbohydrate oxidation minus oxidation of exogenous carbohydrate and was increased by 44% (from 35.8 +/- 5.6 to 51.7 +/- 6.6 g, P < 0.004) during E-M. It is concluded that exercise performed in the fasting state stimulates glycogen turnover and fat oxidation.
Article
The present study was undertaken to examine the effects of glucose ingestion before exercise on liver glucose output and muscle glucose uptake during exercise. On two occasions, at least 1 wk apart, six trained men (peak pulmonary O2 uptake = 5.11 +/- 0.17 l/min) ingested 400 ml of a solution containing either 75 g glucose [carbohydrate (CHO)] or a sweet placebo [control (Con)] 30 min before 60 min of exercise at 71 +/- 1% peak pulmonary O2 uptake. Glucose kinetics (rates of appearance and disappearance) were measured by a primed continuous infusion of [6,6-2H2]glucose. Liver glucose output was derived from total glucose appearance and the appearance of ingested glucose from the gut. After glucose ingestion, plasma glucose increased to 6.4 +/- 0.4 mmol/l immediately before exercise, fell to 4.2 +/- 0.5 mmol/l after 20 min of exercise, and then increased to a higher value than in the Con group (5.4 +/- 0.3 vs. 4.7 +/- 0.1 mmol/l; P < 0.05) after 60 min of exercise. In the CHO group, plasma insulin was higher immediately before exercise (P < 0.05) and, despite falling during exercise, remained higher than in the Con group after 60 min of exercise (57.0 +/- 11.4 vs. 24.8 +/- 1.7 pmol/l; P < 0.05). The rapid fall in plasma glucose in the CHO group was the result of a higher muscle glucose uptake with the onset of exercise (P < 0.05), which could not be matched by the glucose rate of appearance. Liver glucose output was decreased by glucose ingestion, and although it increased during the early stages of exercise in the CHO group, it did not rise above the basal values and was reduced by 62% over the 60 min of exercise compared with the Con group. In summary, preexercise glucose ingestion results in increased muscle glucose uptake and reduced liver glucose output during exercise.
Article
We determined whether increased glycolytic flux from hyperglycemia and hyperinsulinemia directly reduces fatty acid oxidation during exercise. Fatty acid oxidation rates were measured during constant-rate intravenous infusion of trace amounts of a long-chain fatty acid ([1-13C]palmitate; Pal) vs. a medium-chain fatty acid ([1-13C]octanoate; Oct). Six endurance-trained men cycled for 40 min at 50% of maximal O2 uptake 1) after an overnight fast ("fasting") and 2) after ingestion of 1.4 g/kg of glucose at 60 min and again 10 min before exercise (Glc). Glc caused hyperinsulinemia, a preexercise blood glucose of 6 mM, and a 34% reduction in total fat oxidation during exercise due to an approximately equal reduction in oxidation of plasma-free fatty acids (FFA) and intramuscular triglycerides (all P < 0.05). Oxidation of Pal was significantly reduced during Glc compared with fast (i.e., 70.0 +/- 4.1 vs. 86.0 +/- 1.9% of tracer infusion rate; P < 0.05). However, Glc had no effect on Oct oxidation, which is apparently not limited by mitochondrial transport. Furthermore, Glc reduced plasma FFA appearance 36% (P < 0.05), indicating a coordination of effects on adipose tissue and muscle. In summary, substrate oxidation during exercise can be regulated by increased glycolytic flux that is accompanied by a direct inhibition of long-chain fatty acid oxidation. These observations indicate that carbohydrate availability can directly regulate fat oxidation during exercise.
Exercise: Regulation and Integration of Multiple Systems
  • G J Van Der Vusse
  • R S Reneman
Van der Vusse, G. J., and R. S. Reneman. Lipid metabolism in muscle. In: Handbook of Physiology. Exercise: Regulation and Integration of Multiple Systems. Bethesda, MD: Am. Physiol. Soc., 1996, sect. 12, chapt. 21, p. 952-994.
Arbeithypoglykamie nach glukoseeingabe
  • O Bøje
Bøje, O. Arbeithypoglykamie nach glukoseeingabe. Skand. Arch. Physiol. 83: 308-312, 1940.
Influences of glucose loading and of injected insulin on hepatic glucose output
  • R Steele
Steele, R. Influences of glucose loading and of injected insulin on hepatic glucose output. Ann. NY Acad. Sci. 82: 420–430, 1959.
Radioactive and Stable Isotope Tracers in Biomedicine: Principles and Practice of Kinetic Analysis
  • R R Wolfe
Wolfe, R. R. Radioactive and Stable Isotope Tracers in Biomedicine: Principles and Practice of Kinetic Analysis (1st ed.). New York: Wiley-Liss, 1992.
The Elements of the Science of Nutrition
  • G Lusk
Lusk, G. The Elements of the Science of Nutrition. Philadelphia, PA: Saunders, 1928.