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Annual Meeting Abstracts: G-46 – Free Communication/Slide: Protein Metabolism

Effect of Diet on Whole-Body Leucine Oxidation at Rest and During Prolonged Exercise and Recovery in Humans

Howarth, Krista R.; Phillips, Stuart M.; MacDonald, Maureen J.; Richards, Douglas L.; Moreau, Natalie A.; Gibala, Martin J.

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Medicine & Science in Sports & Exercise: May 2004 - Volume 36 - Issue 5 - p S322-S323
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There are data to suggest that pre-exercise diet and/or resting muscle glycogen availability can influence whole-body protein utilization during and following exercise (e.g., Lemon and Mullin, J. Appl. Physiol. 48:624–629, 1980). However, the few previous studies that investigated this topic were limited by the use of indirect markers to assess protein kinetics and/or the lack of rigorous experimental controls. PURPOSE: We employed stable isotope tracer methodology and strict diet and physical activity controls in order to examine the effect of carbohydrate (CHO) availability on whole-body protein turnover at rest and during prolonged exercise and recovery in humans. METHODS: Six men (24 ± 1yr) performed cycle exercise at ∼75% VO2peak to exhaustion in order to reduce body CHO stores, and then consumed either a high- (HC; 6837 ± 518 kcal; 71 ± 2% CHO; 19 ± 3 fat; 10 ± 1% protein) or low- CHO diet (LC; 6172 ± 739; 11 ± 1% CHO; 63 ± 2% fat, 25 ± 2% protein) for ∼2 d. Subjects completed both trials in random order, separated by 2–4 wks. Following each dietary intervention, subjects received a primed constant infusion of 1-13C-leucine (Leu) and whole-body protein kinetics were determined from blood and breath samples obtained at rest, during 2 h of two-legged kicking exercise (Ex) and 1 h of recovery (Recov). Ex was performed on a custom-built ergometer at ∼45% of Wmax. RESULTS: Biopsy samples confirmed that muscle [glycogen] was lower in LC vs HC at rest (430 ± 29 vs 292 ± 30 mmol.kg−1 dry wt) and after Ex and Recov (main effect, P<0.05). Leu oxidation (all values are μmol.kg−1.hr−1.hr) was similar at rest (HC: 32 ± 5 vs LC: 32 ± 3). During Ex, Leu oxidation increased (P<0.05) above rest in the LC trial only (44 ± 3) and was higher (P<0.05) vs HC (32 ± 3). Leu oxidation decreased during Recov in both trials (HC: 13 ± 2, LC: 16 ± 2) and was lower compared to rest and Ex (main effect, P<0.05). CONCLUSION: Whole body Leu oxidation was increased during moderate exercise in humans following ingestion of a LC diet for ∼2 days. There was no exercise-induced increase in Leu oxidation after a HC diet. Finally, Leu oxidation decreased during recovery compared to both rest and exercise, regardless of pre-exercise CHO intake. Supported by NSERC Canada.

©2004The American College of Sports Medicine