scholarly journals Effect of altering substrate availability on metabolism and performance during intense exercise

2000 ◽  
Vol 84 (6) ◽  
pp. 829-838 ◽  
Author(s):  
John A. Hawley ◽  
Louise M. Burke ◽  
Damien J. Angus ◽  
Kieran E. Fallon ◽  
David T. Martin ◽  
...  
Keyword(s):  
Saturated Fat ◽  
Time Trial ◽  
Random Order ◽  
Plasma Free Fatty Acid ◽  
Fat Oxidation ◽  
Carbohydrate Oxidation ◽  
Substrate Selection ◽  
Substrate Availability ◽  
Intense Exercise ◽  
And Performance

The purpose of this study was to determine the effect of altering substrate availability on metabolism and performance during intense cycling. Seven highly trained men ingested a random order of three isoenergetic meals 90 min before cycling at 80 % maximal oxygen uptake (VO2max) for 20 min (about 310 W), followed by a 600 kJ time trial lasting about 30 min. Meals consisted of either 1·2 g saturated fat/kg body mass (BM) with 3500 U heparin intravenously (HIFAT) to elevate circulating plasma free fatty acid (FA) concentration, 2·5 g carbohydrate/kg BM (CHO) to elevate plasma glucose and insulin concentrations or 2·5 g carbohydrate+20 mg nicotinic acid/kg BM (NA) to suppress lipolysis and reduce free FA concentration. HIFAT elevated free FA concentration (HIFAT 1·3 (SEM 0·2), CHO 0·2 (sem 0·1), NA 0·1 (sem 0·1) mm; P<0·001), lowered the RER (HIFAT 0·94 (sem 0·01), CHO 0·97 (sem 0·01), NA 0·98 (sem 0·01); P<0·01) and increased the rate of fat oxidation (HIFAT 24 (sem 3), CHO 12 (sem 2), NA 8 (sem 3) μmol/kg per min; P<0·01) during the 20 min ride. Marked differences in fat availability and fuel utilisation, however, had little effect on performance in the subsequent time trial (HIFAT 320 (sem 16), CHO 324 (sem 15), NA 315 (sem 13) W). We conclude: (1) increased fat availability during intense cycling increases the rate of fat oxidation; but (2) the reduction in the rate of carbohydrate oxidation in the presence of high circulating plasma free FA is unlikely to enhance intense exercise performance lasting about 1 h; (3) substrate selection during intense (about 80 % VO2max) exercise is dominated by carbohydrate oxidation.

No Effect of Pre-exercise Meal on Substrate Metabolism and Time Trial Performance during Intense Endurance Exercise

2003 ◽  
Vol 13 (4) ◽  
pp. 489-503 ◽  
Author(s):  
David Paul ◽  
Kevin A. Jacobs ◽  
Raymond J. Geor ◽  
Kenneth W. Hinchcliff
Keyword(s):  
Lactate Threshold ◽  
Energy Content ◽  
Time Trial ◽  
Fat Oxidation ◽  
Carbohydrate Oxidation ◽  
Whole Body ◽  
Macronutrient Composition ◽  
Glycogen Utilization ◽  
And Performance ◽  
Trial Performance

To determine the effect of macronutrient composition of pre-exercise meals on exercise metabolism and performance, 8 trained men exercised for 30 min above lactate threshold (30LT), followed by a 20-km time trial (TT). Approximately 3.5 h before exercise, subjects consumed a carbohydrate meal (C; 3 g carbohydrate/kg), an isoenergetic fat meal (F; 1.3 g fat/kg), or a placebo meal (P; no energy content) on 3 separate occasions in randomized order. Treatments had no effect on carbohydrate oxidation during exercise, but C decreased whole-body fat oxidation during the last 5 min of 30LT and TT, respectively (3.2 ± 1.6 and 4.8 ± 2.1 mmol · kg−1 · min−1, p < .05) when compared to F (13.3 ± 1.6 and 16.5 ± 2.7 mmol · kg−1 · min−1) and P (15.9 ± 2.7 and 17.0 ± 3.2 mmol · kg−1 · min−1). Glucose rate of appearance (Ra) and disappearance (Rd), and muscle glycogen utilization were not significantly different among treatments during exercise. TT performances were similar for C, F, and P (32.7 ± 0.5 vs. 33.1 ± 1.1 and 33.0 ± 0.8 min, p > .05). We conclude that the consumption of a pre-exercise meal has minor effects on fat oxidation during high-intensity exercise, and no effect on carbohydrate oxidation or TT performance.

scholarly journals Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise

2001 ◽  
Vol 91 (1) ◽  
pp. 115-122 ◽  
Author(s):  
Andrew L. Carey ◽  
Heidi M. Staudacher ◽  
Nicola K. Cummings ◽  
Nigel K. Stepto ◽  
Vasilis Nikolopoulos ◽  
...  
Keyword(s):  
Endurance Exercise ◽  
Power Output ◽  
High Fat Diet ◽  
Respiratory Exchange Ratio ◽  
Time Trial ◽  
Fat Oxidation ◽  
Significant Benefit ◽  
High Fat ◽  
Competitive Athletes ◽  
And Performance

We determined the effect of fat adaptation on metabolism and performance during 5 h of cycling in seven competitive athletes who consumed a standard carbohydrate (CHO) diet for 1 day and then either a high-CHO diet (11 g · kg−1 · day−1 CHO, 1 g · kg−1 · day−1 fat; HCHO) or an isoenergetic high-fat diet (2.6 g · kg−1 · day−1 CHO, 4.6 g · kg−1 · day−1 fat; fat-adapt) for 6 days. On day 8, subjects consumed a high-CHO diet and rested. On day 9, subjects consumed a preexercise meal and then cycled for 4 h at 65% peak O2 uptake, followed by a 1-h time trial (TT). Compared with baseline, 6 days of fat-adapt reduced respiratory exchange ratio (RER) with cycling at 65% peak O2 uptake [0.78 ± 0.01 (SE) vs. 0.85 ± 0.02; P < 0.05]. However, RER was restored by 1 day of high-CHO diet, preexercise meal, and CHO ingestion (0.88 ± 0.01; P < 0.05). RER was higher after HCHO than fat-adapt (0.85 ± 0.01, 0.89 ± 0.01, and 0.93 ± 0.01 for days 2, 8, and 9, respectively; P < 0.05). Fat oxidation during the 4-h ride was greater (171 ± 32 vs. 119 ± 38 g; P < 0.05) and CHO oxidation lower (597 ± 41 vs. 719 ± 46 g; P < 0.05) after fat-adapt. Power output was 11% higher during the TT after fat-adapt than after HCHO (312 ± 15 vs. 279 ± 20 W; P = 0.11). In conclusion, compared with a high-CHO diet, fat oxidation during exercise increased after fat-adapt and remained elevated above baseline even after 1 day of a high-CHO diet and increased CHO availability. However, this study failed to detect a significant benefit of fat adaptation to performance of a 1-h TT undertaken after 4 h of cycling.

Relationship between fatty acid delivery and fatty acid oxidation during strenuous exercise

1995 ◽  
Vol 79 (6) ◽  
pp. 1939-1945 ◽  
Author(s):  
J. A. Romijn ◽  
E. F. Coyle ◽  
L. S. Sidossis ◽  
X. J. Zhang ◽  
R. R. Wolfe
Keyword(s):  
Fatty Acid ◽  
Plasma Free Fatty Acid ◽  
Fat Oxidation ◽  
Carbohydrate Oxidation ◽  
Strenuous Exercise ◽  
Constant Infusion ◽  
Acid Oxidation ◽  
Heparin Infusion ◽  
Plasma Ffa ◽  
Total Fat

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.

scholarly journals Probiotic supplementation increases carbohydrate metabolism in trained male cyclists: a randomized, double-blind, placebo-controlled crossover trial

2020 ◽  
Vol 318 (4) ◽  
pp. E504-E513 ◽  
Author(s):  
Jamie N. Pugh ◽  
Anton J. M. Wagenmakers ◽  
Dominic A. Doran ◽  
Simon C. Fleming ◽  
Barbara A. Fielding ◽  
...  
Keyword(s):  
Time Trial ◽  
Fat Oxidation ◽  
Carbohydrate Oxidation ◽  
Plasma Metabolites ◽  
Nonesterified Fatty Acid ◽  
Probiotic Supplementation ◽  
Time Trial Performance ◽  
Oxidation Rates ◽  
Subsequent Time ◽  
Trial Performance

We hypothesized that probiotic supplementation (PRO) increases the absorption and oxidation of orally ingested maltodextrin during 2 h endurance cycling, thereby sparing muscle glycogen for a subsequent time trial (simulating a road race). Measurements were made of lipid and carbohydrate oxidation, plasma metabolites and insulin, gastrointestinal (GI) permeability, and subjective symptoms of discomfort. Seven male cyclists were randomized to PRO (bacterial composition given in methods) or placebo for 4 wk, separated by a 14-day washout period. After each period, cyclists consumed a 10% maltodextrin solution (initial 8 mL/kg bolus and 2 mL/kg every 15 min) while exercising for 2 h at 55% maximal aerobic power output, followed by a 100-kJ time trial. PRO resulted in small increases in peak oxidation rates of the ingested maltodextrin (0.84 ± 0.10 vs. 0.77 ± 0.09 g/min; P = 0.016) and mean total carbohydrate oxidation (2.20 ± 0.25 vs. 1.87 ± 0.39 g/min; P = 0.038), whereas fat oxidation was reduced (0.40 ± 0.11 vs. 0.55 ± 0.10 g/min; P = 0.021). During PRO, small but significant increases were seen in glucose absorption, plasma glucose, and insulin concentration and decreases in nonesterified fatty acid and glycerol. Differences between markers of GI damage and permeability and time-trial performance were not significant ( P > 0.05). In contrast to the hypothesis, PRO led to minimal increases in absorption and oxidation of the ingested maltodextrin and small reductions in fat oxidation, whereas having no effect on subsequent time-trial performance.

Effect of High-Fat, High-Carbohydrate, and High-Protein Meals on Metabolism and Performance during Endurance Cycling

2002 ◽  
Vol 12 (3) ◽  
pp. 318-335 ◽  
Author(s):  
David S. Rowlands ◽  
Will G. Hopkins
Keyword(s):  
Oxidation Rate ◽  
Peak Power ◽  
Time Trial ◽  
Fat Oxidation ◽  
High Protein ◽  
High Fat ◽  
High Carbohydrate ◽  
Competitive Cyclists ◽  
And Performance ◽  
Meal Composition

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.

scholarly journals The Effects of Acute Ingestion of a High-fat Solution, compared to a High-Carbohydrate Solution, on Skeletal Muscle Oxygenation, Fat Oxidation and Performance During a 2-hour Cycling Effort Followed by a Short Time Trial in Cyclists and Triathletes

2021 ◽  
Vol 3 (122) ◽  
pp. 42-58
Author(s):  
Antoine Jolicoeur Desroches ◽  
Frédéric Domingue ◽  
Louis Laurencelle ◽  
Claude Lajoie
Keyword(s):  
Skeletal Muscle ◽  
Perceived Exertion ◽  
Near Infrared ◽  
Time Trial ◽  
Fat Oxidation ◽  
Muscle Oxygenation ◽  
Skeletal Muscle Oxygenation ◽  
And Performance ◽  
Maximal Effort ◽  
Carbohydrate Solution

This study aimed to determine the effects of consuming a high fat solution (HFS) compared to a high carbohydrate solution (HCS) during a cycling effort on substrate oxidation, muscle oxygenation and performance with cyclists and triathletes. Thirteen men participated in this study (age: 30.4 ± 6.3 y; height: 178.7 ± 6.1 cm; weight: 74.9 ± 6.5 kg; V̇O2 peak: 60.5 ± 7.9 mlO2×kg-1×min-1). The solutions were isocaloric (total of 720 kcal) and were consumed every 20 minutes. Each solution of HFS contained 12.78 g of lipids, 1.33 g of carbohydrates and 0.67 g of proteins, and each solution of HCS contained 28 g of carbohydrates. We measured pulmonary oxygen consumption and skeletal muscle oxygenation, using a Near Infrared Spectrometer (NIRS) during a cycling effort consisting of 2 hours at 65 % of maximal aerobic power (MAP) followed immediately by a 3-minute time-trial (TT). We observed that the consumption of the HFS increased the rate of fat oxidation at the end of the sub-maximal effort (0.61 ± 0.14 vs 0.53 ± 0.17 g×min-1, p < 0.05). We have also shown that the HFS negatively affected the performance in the TT (mean Watts: HCS: 347.0 ± 77.4 vs HFS: 326.5 ± 88.8 W; p < 0.05) and the rating of perceived exertions during the sub-maximal effort (modified Borg Perceived Exertion scale: 1–10) (mean: 3.62 ± 0.58 for HCS vs 4.16 ± 0.62 for HFS; p < 0.05). We did not observe a significant effect of the acute consumption of the HFS compared to the HCS on muscle oxygenation during the cycling effort. Finally, we observed that cyclists who demonstrated a high skeletal muscle deoxygenation relative to their pulmonary oxygen consumption (DHHb/V̇O2) had a higher fat oxidation capacity (higher Fatmax). In conclusion, even though the consumption of HFS increased the rate of fat oxidation at the end of a sub-maximal effort, it did not affect muscle oxygenation and it negatively affected performance and perceived exertion during a time-trial and caused gastro-intestinal distress in some participants. Keywords: Fat oxidation, Skeletal muscle oxygenation, Lipid supplementation, Carbohydrate supplementation, Near Infrared Spectroscopy (NIRS), Cycling, Triathlon.

Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling

2000 ◽  
Vol 89 (6) ◽  
pp. 2413-2421 ◽  
Author(s):  
Louise M. Burke ◽  
Damien J. Angus ◽  
Gregory R. Cox ◽  
Nicola K. Cummings ◽  
Mark A. Febbraio ◽  
...  
Keyword(s):  
Muscle Glycogen ◽  
High Fat Diet ◽  
Performance Testing ◽  
Time Trial ◽  
Random Order ◽  
Cycling Performance ◽  
High Fat ◽  
Glycogen Utilization ◽  
And Performance ◽  
Glycogen Sparing

For 5 days, eight well-trained cyclists consumed a random order of a high-carbohydrate (CHO) diet (9.6 g · kg−1 · day−1 CHO, 0.7 g · kg−1 · day−1 fat; HCHO) or an isoenergetic high-fat diet (2.4 g · kg−1 · day−1 CHO, 4 g · kg−1 · day−1 fat; Fat-adapt) while undertaking supervised training. On day 6,subjects ingested high CHO and rested before performance testing on day 7 [2 h cycling at 70% maximal O2consumption (SS) + 7 kJ/kg time trial (TT)]. With Fat-adapt, 5 days of high-fat diet reduced respiratory exchange ratio (RER) during cycling at 70% maximal O2 consumption; this was partially restored by 1 day of high CHO [0.90 ± 0.01 vs. 0.82 ± 0.01 ( P < 0.05) vs. 0.87 ± 0.01 ( P < 0.05), for day 1, day 6, and day 7, respectively]. Corresponding RER values on HCHO trial were [0.91 ± 0.01 vs. 0.88 ± 0.01 ( P < 0.05) vs. 0.93 ± 0.01 ( P < 0.05)]. During SS, estimated fat oxidation increased [94 ± 6 vs. 61 ± 5 g ( P < 0.05)], whereas CHO oxidation decreased [271 ± 16 vs. 342 ± 14 g ( P < 0.05)] for Fat-adapt compared with HCHO. Tracer-derived estimates of plasma glucose uptake revealed no differences between treatments, suggesting muscle glycogen sparing accounted for reduced CHO oxidation. Direct assessment of muscle glycogen utilization showed a similar order of sparing (260 ± 26 vs. 360 ± 43 mmol/kg dry wt; P = 0.06). TT performance was 30.73 ± 1.12 vs. 34.17 ± 2.48 min for Fat-adapt and HCHO ( P = 0.21). These data show significant metabolic adaptations with a brief period of high-fat intake, which persist even after restoration of CHO availability. However, there was no evidence of a clear benefit of fat adaptation to cycling performance.

scholarly journals Nutrient Oxidation during Moderately Intense Exercise in Obese Prepubertal Boys

2005 ◽  
Vol 90 (1) ◽  
pp. 231-236 ◽  
Author(s):  
C. Maffeis ◽  
M. Zaffanello ◽  
M. Pellegrino ◽  
C. Banzato ◽  
G. Bogoni ◽  
...  
Keyword(s):  
Body Mass Index ◽  
Oxygen Uptake ◽  
Oxidation Rate ◽  
Walking Speed ◽  
Fat Oxidation ◽  
Carbohydrate Oxidation ◽  
Intense Exercise ◽  
Prepubertal Boys ◽  
Oxidation Ratio ◽  
Different Levels

Abstract The aim of this study was to measure the nutrient oxidation rate during walking at different speeds and to identify the walking speed associated with the highest fat oxidation rate in a group of prepubertal boys with different levels of adiposity. Twenty-four prepubertal boys (age, 10 ± 1 yr) with different levels of overweight (body mass index, 25.5 ± 3.5 kg/m2; sd score of body mass index, 3.4 ± 1.1) performed a treadmill test. We measured by indirect calorimetry their respiratory exchange while they walked at speeds of 4, 5, and 6 km/h as well as their maximal oxygen uptake. The fat oxidation rate did not change significantly when the speed of walking was increased, whereas carbohydrate oxidation increased significantly (P &lt; 0.001). A significant (P &lt; 0.05) association was found between adiposity (percent fat mass) and the fat to carbohydrate oxidation ratio during walking at 4, 5, and 6 km/h (r = 0.37, r = 0.37, and r = 0.36, respectively), adjusting for exercise intensity (maximal oxygen uptake, percentage). The lowest fat to carbohydrate oxidation ratio, i.e. the highest fat oxidation/carbohydrate oxidation rate, was found at a walking speed of 4 km/h. Moderately intense exercise promoted the highest fat to carbohydrate oxidation ratio. Increasing the exercise intensity did not promote fat oxidation. Therefore, walking at a speed of 4 km/h is recommended as practicable exercise for obese boys and, consequently, for the treatment of childhood obesity.

Nighttime feeding likely alters morning metabolism but not exercise performance in female athletes

2016 ◽  
Vol 41 (7) ◽  
pp. 719-727 ◽  
Author(s):  
Michael J. Ormsbee ◽  
Katherine A. Gorman ◽  
Elizabeth A. Miller ◽  
Daniel A. Baur ◽  
Lisa A. Eckel ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Female Athletes ◽  
Resting Metabolic Rate ◽  
Time Trial ◽  
Early Morning ◽  
Carbohydrate Oxidation ◽  
Peak Oxygen Consumption ◽  
Hydration Status ◽  
Total Carbohydrate ◽  
Running Performance

The timing of morning endurance competition may limit proper pre-race fueling and resulting performance. A nighttime, pre-sleep nutritional strategy could be an alternative method to target the metabolic and hydrating needs of the early morning athlete without compromising sleep or gastrointestinal comfort during exercise. Therefore, the purpose of this investigation was to examine the acute effects of pre-sleep chocolate milk (CM) ingestion on next-morning running performance, metabolism, and hydration status. Twelve competitive female runners and triathletes (age, 30 ± 7 years; peak oxygen consumption, 53 ± 4 mL·kg−1·min−1) randomly ingested either pre-sleep CM or non-nutritive placebo (PL) ∼30 min before sleep and 7–9 h before a morning exercise trial. Resting metabolic rate (RMR) was assessed prior to exercise. The exercise trial included a warm-up, three 5-min incremental workloads at 55%, 65%, and 75% peak oxygen consumption, and a 10-km treadmill time trial (TT). Physiological responses were assessed prior, during (incremental and TT), and postexercise. Paired t tests and magnitude-based inferences were used to determine treatment differences. TT performances were not different (“most likely trivial” improvement with CM) between conditions (PL: 52.8 ± 8.4 min vs CM: 52.8 ± 8.0 min). RMR was “likely” increased (4.8%) and total carbohydrate oxidation (g·min−1) during exercise was “possibly” or likely increased (18.8%, 10.1%, 9.1% for stage 1–3, respectively) with CM versus PL. There were no consistent changes to hydration indices. In conclusion, pre-sleep CM may alter next-morning resting and exercise metabolism to favor carbohydrate oxidation, but effects did not translate to 10-km running performance improvements.

Changes in 24-h substrate oxidation in older and younger men in response to exercise

2007 ◽  
Vol 103 (5) ◽  
pp. 1576-1582 ◽  
Author(s):  
Edward L. Melanson ◽  
William T. Donahoo ◽  
Gary K. Grunwald ◽  
Robert Schwartz
Keyword(s):  
Fatty Acids ◽  
Energy Expenditure ◽  
Free Fatty Acids ◽  
Plasma Free Fatty Acid ◽  
Fat Oxidation ◽  
Substrate Oxidation ◽  
Net Energy ◽  
Younger Men ◽  
Response To Exercise ◽  
Time Point

The purpose of this study was to compare 24-h substrate oxidation in older (OM; 60–75 yr, n = 7) and younger (YM; 20–30 yr, n = 7) men studied on sedentary day (Con) and on a day with exercise (Ex; net energy expenditure = 300 kcal). Plasma glucose and free fatty acids were also measured at several time points during the 24-h measurement. Weight was not different in OM and YM (means ± SD; 84.8 ± 16.9 vs. 81.4 ± 10.4 kg, respectively), although percent body fat was slightly higher in OM (25.9 ± 3.5 vs. 21.9 ± 9.7%; P = 0.17).Values of 24-h energy expenditure did not differ in OM and YM on the Con (means ± SE; 2,449 ± 162 vs. 2,484 ± 104 kcal/day, respectively) or Ex (2,902 ± 154 vs. 2,978 ± 122 kcal/day) days. Under both conditions, 24-h respiratory quotient was significantly lower and fat oxidation significantly higher in OM. Glucose concentrations were not different at any time point, but plasma free fatty acid concentrations were higher in OM, particularly following meals. Thus, under these controlled conditions, 24-h fat oxidation was not reduced and was in fact greater in OM. We speculate that differences in the availability of circulating free fatty acids in the postprandial state contributed to the observed differences in 24-h fat oxidation in OM and YM.

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