BCAAs (Branched-Chain Amino Acids - leucine, isoleucine, and valine) were one of the most popular supplements of the 2000s and 2010s. Recent research has significantly tempered their claims and shifted expert consensus toward EAAs (Essential Amino Acids, which include all 9 amino acids the body cannot produce). The reality is nuanced and depends heavily on your overall protein intake.
BCAAs: the case for. During fasted training (training before eating), BCAAs can reduce muscle breakdown. Leucine specifically is the key trigger for muscle protein synthesis. A BCAA drink during training may reduce muscle soreness. The case against: if you're eating adequate protein (1.6-2.2g per kg body weight daily), the additional BCAAs provide minimal benefit. Research consistently shows that whole food protein and whey protein outperform isolated BCAAs for muscle growth because they contain all essential amino acids, not just three.
EAAs are a better choice than BCAAs because they contain all amino acids required for complete muscle protein synthesis. However, if you're consuming adequate total protein, even EAAs provide minimal additional benefit. The practical conclusion: if you eat enough protein from food and supplements, skip the BCAAs and EAAs - the money is better spent on protein powder or creatine. If you train fasted, consume a small protein dose (10-20g whey or EAA) pre-workout to prevent muscle catabolism. The expensive flavoured BCAA drinks in fancy bottles are largely a marketing success story rather than a performance enhancement necessity.