BCAAs

Useful only when total protein intake is suboptimal. For most people eating adequate protein, standalone BCAAs offer little additional benefit over food.

A rough internal score reflecting quantity, quality, and consistency of human evidence. Not a clinical recommendation.

Leucine is a validated mTOR activator. However, meta-analyses show BCAAs alone are inferior to complete protein for muscle protein synthesis because the other EAAs become rate-limiting.

• Leucine stimulates mTOR signalling
• May reduce perceived exertion during endurance exercise
• Useful when whole-protein intake is impractical

5–10 g peri-workout in a 2:1:1 leucine:isoleucine:valine ratio. Less relevant if protein intake exceeds 1.6 g/kg/day.

• Nausea at high doses
• Theoretical serotonin interference

Excessive BCAA intake may impair serotonin synthesis (competes with tryptophan at the BBB). Caution in maple syrup urine disease.

The supplement industry has overstated BCAA benefits relative to whey or EAAs. Context of total diet matters enormously.

• Muscle42
• Recovery40
• Energy30