Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?
Wolfe RR
Evidence is still building up
Summary
The claim that dietary BCAA intake alone stimulates muscle protein synthesis is unwarranted. While leucine activates mTOR signaling, the absence of other essential amino acids (EAAs) means the body must catabolize existing muscle to obtain missing substrates. Maximal MPS requires the full complement of EAAs.
Key findings
- 1
BCAA alone can theoretically stimulate MPS by up to ~30%, but missing EAAs limit actual anabolic impact
- 2
Intravenous BCAA infusion studies showed decreases in both MPS and muscle protein breakdown — no net anabolic effect
- 3
Maximal MPS requires all essential amino acids, not just BCAAs
- 4
When dietary protein intake is adequate, additional BCAA supplementation shows no meaningful additive benefit
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