The branched-chain amino acids (BCAA) – leucine, isoleucine, and valine – are unique among amino acids in that they are primarily metabolized extrahepatically in skeletal muscle. In muscle, the BCAA serve as both an important energy substrate during exercise and periods of stress, and as a precursor for the synthesis of other amino acids and proteins. Initial research into BCAA focused on both their anabolic effects in particular in catabolic disease states,

BCAA exert significant influences on glutamine metabolism. Glutamine is recognized as an important nutrient to many rapidly dividing cells in the body, especially in the gut and the immune system.

The BCAA serve as an oxidative substrate for skeletal muscle during periods of prolonged exercise. In a study of runners in the Brussel’s marathon, the plasma concentrations of glutamine, alanine and BCAA were found to be decreased immediately after the marathon, but had returned to pre-exercise levels within 16 hour

BCAAs (leucine, isoleucine, and valine), particularly leucine, have anabolic effects on protein metabolism by increasing the rate of protein synthesis and decreasing the rate of protein degradation in resting human muscle. Also, during recovery from endurance exercise, BCAAs were found to have anabolic effects in human muscle.

The fatty acids may be one of the regulators of BCAA catabolism and that the BCAA requirement is increased by exercise. Furthermore, BCAA supplementation before and after exercise has beneficial effects for decreasing exercise-induced muscle damage and promoting muscle-protein synthesis; this suggests the possibility that BCAAs are a useful supplement in relation to exercise and sports.