Branched-Chain Amino Acid (BCAA)

A collective term for three essential amino acids that share a branched aliphatic side chain: L-Leucine, L-Isoleucine, and L-Valine. Unlike most amino acids, BCAAs are primarily catabolised in skeletal muscle rather than the liver. The 2:1:1 ratio (leucine:isoleucine:valine) is the most commonly used commercial blend in sports nutrition. The evidence for isolated BCAA supplementation as a standalone muscle-building intervention in well-nourished athletes is limited and contested; see Section 21 (BCAA 2:1:1) and Section 43 (Individual BCAAs) for detailed evidence discussion.