Carbohydrate, protein and fat metabolism during exercise after oral carnitine supplementation in humans

Abstract

Twenty non-vegetarian active males were pair-matched and randomly assigned to receive 2 g L-Carnitine L-tartrate (LC).d-1 or placebo for 2 weeks. Subjects exercised for 90 min at 70% O2max following 2 days of a prescribed diet (mean ± SD: 13.6 ± 1.6 MJ, 57% carbohydrate, 15% protein, 26% fat, 2% alcohol) before and after supplementation. Results indicated no change in carbohydrate oxidation, nitrogen excretion, branched-chain amino acid oxidation, or plasma urea during exercise between the beginning and end of supplementation in either group. Following 2 weeks LC supplementation the plasma ammonia response to exercise tended to be suppressed (0 vs. 2wk at 60 min exercise: 97 ± 26 vs. 80 ± 9; and 90 min exercise: 116 ± 47 vs. 87 ± 25 µmol.L-1), with no change in the placebo group. The data indicate that 2 weeks of LC supplementation does not affect fat, carbohydrate and protein contribution to metabolism during prolonged moderate intensity cycling exercise. However, the tendency towards suppressed ammonia accumulation indicates that oral LC supplementation may have the potential to reduce the metabolic stress of exercise or alter ammonia production/removal which warrants further investigation.