Concluding remarks

It is clear that exercise promotes degradation of BCAAs. Promotion of fatty acid oxidation appears to be associated with greater rates of BCAA oxidation, which suggests that fatty acids may be regulators of BCAA oxidation. Furthermore, muscle-protein synthesis is enhanced after exercise. From these findings, it may be concluded that the BCAA requirement is increased by exercise. BCAA supplementation before and after exercise has beneficial effects for decreasing exercise-induced muscle damage and promoting muscle-protein synthesis; this suggests that BCAAs may be a useful supplement in relation to exercise and sports. Although in many human exercise studies, a dose of >5 g of BCAA was used as a supplement, the minimum dose to produce the beneficial effects of BCAA supplementation remains to be established. Furthermore, the most effective ratio of the three BCAAs is unclear. Toxicity studies of BCAAs using animals showed that BCAAs are quite safe amino acids when the three BCAAs are provided in a ratio similar to that of animal protein (e.g., a 2:1:1 leucine:isoleucine:valine ratio).

Although leucine is the most potent amino acid among the BCAAs for stimulating protein synthesis, supplementation of leucine alone may cause BCAA imbalance via the activating effect of its keto acid on the BCKDH complex. A number of research groups examined whether BCAA supplementation might have a beneficial effect on endurance performance (32–36), but the results are inconsistent. Additional studies are required to clarify the appropriate amount of BCAA supplementation for beneficial effects and the responsible mechanisms.