Endurance Exercise Attenuates Postprandial Whole-Body Leucine Balance in Trained Men

Purpose: Endurance exercise increases indices of small intestinal damage and leucine oxidation, which may attenuate dietary amino acid appearance and postprandial leucine balance during postexercise recovery. Therefore, the purpose of this study was to examine the effect of an acute bout of endurance exercise on postprandial leucine kinetics and net leucine balance. Methods: In a crossover design, seven trained young men (age = 25.6 2.3 yr; (V) over dotO(2peak) = 61.4 2.9 mL.kg(-1).min(-1); mean +/- SEM) received a primed constant infusion of L-[1-C-13]leucine before and after ingesting a mixed macronutrient meal containing 18 g whole egg protein intrinsically labeled with L-[5,5,5-H-2(3)]leucine, 17 g fat, and 60 g carbohydrate at rest and after 60 min of treadmill running at 70% (V) over dotO(2peak). Results: Plasma intestinal fatty acid binding protein concentrations and leucine oxidation both increased (P < 0.01) to peaks that were similar to 2.5-fold above baseline values during exercise with a concomitant decrease (P < 0.01) in nonoxidative leucine disposal. Meal ingestion attenuated (P < 0.01) endogenous leucine rates of appearance at rest and after exercise. There were no differences (both, P > 0.05) in dietary leucine appearance rates or in the amount of dietary protein-derived leucine that appeared into circulation over the 5-h postprandial period at rest and after exercise (62% +/- 2% and 63% +/- 2%, respectively). Leucine balance over the 5-h postprandial period was positive (P < 0.01) in both conditions but was negative (P < 0.01) during the exercise trial after accounting for exercise-induced leucine oxidation. Conclusions: We demonstrate that endurance exercise does not modulate dietary leucine availability from a mixed meal but attenuates postprandial whole-body leucine balance in trained young men.