A Protein-Leucine Supplement Increases Branched-Chain Amino Acid and Nitrogen Turnover But Not Performance

NELSON, A. R., S. M. PHILLIPS, T. STELLINGWERFF, S. REZZI, S. J. BRUCE, I. BRETON, A. THORIMBERT, P. A. GUY, J. CLARKE, S. BROADBENT, and D. S. ROWLANDS. A Protein-Leucine Supplement Increases Branched-Chain Amino Acid and Nitrogen Turnover But Not Performance. Med. Sci. Sports Exerc., Vol. 44, No. 1, pp. 57-68, 2012. Purpose: This study aimed to determine the effect of postexercise protein-leucine coingestion with CHO-lipid on subsequent high-intensity endurance performance and to investigate candidate mechanisms using stable isotope methods and metabolomics. Methods: In this double-blind, randomized, crossover study, 12 male cyclists ingested a leucine/protein/CHO/fat supplement (LEUPRO 7.5/20/89/22 g center dot h(-1), respectively) or isocaloric CHO/fat control (119/22 g center dot h(-1)) 1-3 h after exercise during a 6-d training block (intense intervals, recovery, repeated-sprint performance rides). Daily protein intake was clamped at 1.9 g center dot kg(-1)center dot d(-1) (LEUPRO) and 1.5 g center dot kg(-1)center dot d(-1) (control). Stable isotope infusions (1-C-13-leucine and 6,6-H-2(2)-glucose), mass spectrometry-based metabolomics, and nitrogen balance methods were used to determine the effects of LEUPRO on whole-body branched-chain amino acid (BCAA) and glucose metabolism and protein turnover. Results: After exercise, LEUPRO increased BCAA levels in plasma (2.6-fold; 90% confidence limits = x/(sic)1.1) and urine (2.8-fold; x/(sic)1.2) and increased products of BCAA metabolism plasma acylcarnitine C5 (3.0-fold; x/(sic)0.9) and urinary leucine (3.6-fold; x/(sic)1.3) and A-aminoisobutyrate (3.4-fold; x/(sic)1.4), indicating that ingesting similar to 10 g leucine per hour during recovery exceeds the capacity to metabolize BCAA. Furthermore, LEUPRO increased leucine oxidation (5.6-fold; x/(sic)1.1) and nonoxidative disposal (4.8-fold; x/(sic)1.1) and left leucine balance positive relative to control. With the exception of day 1 (LEUPRO = 17 +/- 20 mg N center dot kg(-1), control = -90 +/- 44 mg N center dot kg(-1)), subsequent (days 2-5) nitrogen balance was positive for both conditions (LEUPRO = 130 +/- 110 mg N center dot kg(-1), control = 111 +/- 86 mg N center dot kg(-1)). Compared with control feeding, LEUPRO lowered the serum creatine kinase concentration by 21%-25% (90% confidence limits = +/- 14%), but the effect on sprint power was trivial (day 4 = 0.4% +/- 1.0%, day 6 = -0.3% +/- 1.0%). Conclusions: Postexercise protein-leucine supplementation saturates BCAA metabolism and attenuates tissue damage, but effects on subsequent intense endurance performance may be inconsequential under conditions of positive daily nitrogen balance.