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Christopher C. Webster, Jeroen Swart, Timothy D. Noakes, and James A. Smith

Low-carbohydrate high-fat (LCHF) diets have gained in popularity among some ultraendurance athletes because they increase rates of fat oxidation during exercise and “spare” muscle glycogen. 1 However, prevailing opinion holds that carbohydrate restriction would compromise exercise performance at

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Joanne G. Mirtschin, Sara F. Forbes, Louise E. Cato, Ida A. Heikura, Nicki Strobel, Rebecca Hall, and Louise M. Burke

nutrition practices and food choices of three different sports nutrition philosophies (high carbohydrate [CHO] availability [HCHO], periodized CHO availability [PCHO], and the ketogenic low-CHO, high-fat [LCHF] diet), noting that these seem to be misunderstood across the scientific literature, social media

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Iñigo Mujika

). Although trained endurance athletes exhibit an enhanced capacity for fat mobilization, transport, and oxidation, it can be further upregulated by short-term (∼5 days) exposure to a low-CHO, high-fat diet (LCHF; <20% energy from CHO and >60% energy from fat), even after acute restoration of high CHO

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Christopher C. Webster, Kathryn M. van Boom, Nur Armino, Kate Larmuth, Timothy D. Noakes, James A. Smith, and Tertius A. Kohn

There is growing interest in low-carbohydrate, high-fat (LCHF) diets (∼50 g/day of carbohydrate) for their potential to improve insulin resistance and type 2 diabetes (T2D) ( Bueno et al., 2013 ; Feinman et al., 2015 ; Hallberg et al., 2019 ). Within athletic populations, an increasing number of

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Victoria L. Bowden and Robert G. McMurray

The purpose of this study was to determine if there is a difference between the way in which aerobically trained and untrained women metabolize fats and carbohydrates at rest in response to either a high-fat or high-carbohydrate meal. Subjects, 6 per group, were fed a high CHO meal (2068 kJ, 76% CHO. 23% fat, 5% protein) and a high fat meal (2093 kJ, 21% CHO, 72% fat, 8% protein) in counterbalanced order. Resting metabolic rate (RMR) was measured every half-hour for 5 hours. RMR was similar between groups. Training status had no overall effect on postprandial metabolic rate or total energy expenditure. The high fat meal resulted in no significant differences in RMR or respiratory exchange ratio (RER) between groups. However, after ingesting a high CHO meal, trained subjects had a peak in metabolism at minute 60, not evident in the untrained subjects. In addition, postprandial RER from minutes 120-300 were lower and fat use was greater after the high CHO meal for the trained subjects. These results suggest that aerobically trained women have an accelerated CHO uptake and overall lower CHO oxidation following the ingestion of a high CHO meal.

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Soo Hyun Park, Eun Sun Yoon, Yong Hee Lee, Chul-Ho Kim, Kanokwan Bunsawat, Kevin S. Heffernan, Bo Fernhall, and Sae Young Jae

Background:

We tested the hypothesis that an active video game following a high-fat meal would partially prevent the unfavorable effect of a high-fat meal on vascular function in overweight adolescents.

Methods:

Twenty-four overweight adolescents were randomized to either a 60-minute active video game (AVG) group (n = 12) or seated rest (SR) as a control group (n = 12) after a high-fat meal. Blood parameters were measured, and vascular function was measured using brachial artery flow-mediated dilation (FMD) at baseline and 3 hours after a high-fat meal.

Results:

No significant interaction was found in any blood parameter. A high-fat meal significantly increased blood triglyceride and glucose concentrations in both groups in a similar manner. Brachial artery FMD significantly decreased in the SR group (13.8 ± 3.2% to 11.8 ± 2.5), but increased in the AVG group (11.4 ± 4.0% to 13.3 ± 3.5), with a significant interaction (P = .034).

Conclusion:

These findings show that an active video game attenuated high-fat meal-induced endothelial dysfunction. This suggests that an active video game may have a cardioprotective effect on endothelial function in overweight adolescents when exposed to a high-fat meal.

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Jesse Fleming, Matthew J. Sharman, Neva G. Avery, Dawn M. Love, Ana L. Gómez, Timothy P. Scheett, William J. Kraemer, and Jeff S. Volek

The effects of adaptation to a high-fat diet on endurance performance are equivocal, and there is little data regarding the effects on high-intensity exercise performance. This study examined the effects of a high-fat/moderate protein diet on submaximal, maximal, and supramaximal performance. Twenty non-highly trained men were assigned to either a high-fat/moderate-protein (HFMP; 61% fat) diet (n = 12) or a control (C; 25% fat) group (n = 8). A maximal oxygen consumption test, two 30-s Wingate anaerobic tests, and a 45-min timed ride were performed before and after 6 weeks of diet and training. Body mass decreased significantly (–2.2 kg; p ≤ .05) in HFMP subjects. Maximal oxygen consumption significantly decreased in the HFMP group (3.5 ± 0.14 to 3.27 ± 0.09 L · min−1) but was unaffected when corrected for body mass. Perceived exertion was significantly higher during this test in the HFMP group. Main time effects indicated that peak and mean power decreased significantly during bout 1 of the Wingate sprints in the HFMP (–10 and –20%, respectively) group but not the C (–8 and –16%, respectively) group. Only peak power was lower during bout 1 in the HFMP group when corrected for body mass. Despite significantly reduced RER values in the HFMP group during the 45-min cycling bout, work output was significantly decreased (–18%). Adaptation to a 6-week HFMP diet in non-highly trained men resulted in increased fat oxidation during exercise and small decrements in peak power output and endurance performance. These deleterious effects on exercise performance may be accounted for in part by a reduction in body mass and/or increased ratings of perceived exertion.

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Matthew Erlenbusch, Mark Haub, Kathy Munoz, Susan MacConnie, and Belinda Stillwell

The purpose of this investigation was to clarify, via a meta-analysis, whether the literature favors a high-fat or a high-carbohydrate diet to yield superior endurance exercise performance. Twenty published trials were analyzed to compare exercise performance under different diets. The average effect size of −0.60 indicated that subjects following a high-carbohydrate diet exercised longer until exhaustion. The training status of subjects (trained vs. untrained) was significantly related to effect size (r = −0.576, P < 0.01) and effect sizes separated between trained and untrained subjects were −0.05 and −2.84 respectively. The test for homogeneity revealed significant heterogeneity among effect sizes (χ2 [19] = 43.30, P < 0.05), indicating all of the trials are not describing the same effect. Given this significant heterogeneity, a conclusive endorsement of a high-carbohydrate diet based on the literature is difficult to make. Highly dissimilar trial protocols are the primary reason for heterogeneity.

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David S. Rowlands and Will G. Hopkins

The effect of pre-exercise meal composition on metabolism and performance in cycling were investigated in a crossover study. Twelve competitive cyclists ingested high-fat, high-carbohydrate, or high-protein meals 90 min before a weekly exercise test. The test consisted of a 1-hour pre-load at 55% peak power, five 10-min incremental loads from 55 to 82% peak power (to measure the peak fat-oxidation rate), and a 50-km time trial that included three 1-km and 4-km sprints. A carbohydrate supplement was ingested throughout the exercise. Relative to the high-protein and high-fat meals, the high-carbohydrate meal halved the peak fat-oxidation rate and reduced the fat oxidation across all workloads by a factor of 0.20 to 0.58 (p = .002–.0001). Reduced fat availability may have accounted for this reduction, as indicated by lower plasma fatty acid, lower glycerol, and higher pre-exercise insulin concentrations relative to the other meals (p = .04–.0001). In contrast, fat oxidation following the high-protein meal was similar to that following the high-fat meal. This similarity was linked to evidence suggesting greater lipolysis and plasma fat availability following high-protein relative to high-carbohydrate meals. Despite these substantial effects on metabolism, meal composition had no clear effect on sprint or 50-km performance.

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Heidi M. Staudacher, Andrew L. Carey, Nicola K. Cummings, John A. Hawley, and Louise M. Burke

We determined the effect of a high-fat diet and carbohydrate (CHO) restoration on substrate oxidation and glucose tolerance in 7 competitive ultra-endurance athletes (peak oxygen uptake [V̇O2peak] 68 ± 1 ml · kg−1 · min−1; mean±SEM). For 6 days, subjects consumed a random order of a high-fat (69% fat; FAT-adapt) or a high-CHO (70% CHO; HCHO) diet, each followed by 1 day of a high-CHO diet. Treatments were separated by an 18-day wash out. Substrate oxidation was determined during submaximal cycling (20 min at 65% V̇O2peak) prior to and following the 6 day dietary interventions. Fat oxidation at baseline was not different between treatments (17.4 ± 2.1 vs. 16.1 ± 1.3 g · 20 min−1 for FAT-adapt and HCHO, respectively) but increased 34% after 6 days of FAT-adapt (to 23.3 ± 0.9 g · 20 min−1, p < .05) and decreased 30% after HCHO (to 11.3±1.4 g · 20 min−1, p < .05). Glucose tolerance, determined by the area under the plasma [glucose] versus time curve during an oral glucose tolerance (OGTT) test, was similar at baseline (545±21 vs. 520±28 mmol · L−1 · 90 min−1), after 5-d of dietary intervention (563 ± 26 vs. 520 ± 18 mmol · L−1 · 90 min−1) and after 1 d of high-CHO (491 ± 28 vs. 489 ± 22 mmol · L−1 · 90min−1 for FAT- adapt and HCHO, respectively). An index of whole-body insulin sensitivity (SI 10000/÷fasting [glucose] × fasting [insulin] × mean [glucose] during OGTT × mean [insulin] during OGTT) was similar at baseline (15 ± 2 vs. 17 ± 5 arbitrary units), after 5-d of dietary intervention (15 ± 2 vs. 15 ± 2) and after 24 h of CHO loading (17 ± 3 vs. 18 ± 2 for FAT- adapt and HCHO, respectively). We conclude that despite marked changes in the pattern of substrate oxidation during submaximal exercise, short-term adaptation to a high-fat diet does not alter whole-body glucose tolerance or an index of insulin sensitivity in highly-trained individuals.