Essential Amino Acids, Leucine, and BCAAs
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The 9 essential amino acids — especially leucine — drive muscle protein synthesis; whole protein beats isolated BCAAs when total protein is adequate.
Detail
Proteins are built from 20 amino acids; 9 are essential (EAAs) and must come from the diet (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine). The EAAs — not the non-essential ones — are what trigger muscle protein synthesis (MPS) (see Muscle Hypertrophy). The ISSN notes that roughly 10 g of EAAs, whether free-form or within a 20–40 g protein bolus, maximally stimulates MPS.
Leucine is the key signaling amino acid: it activates the mTOR pathway that switches on MPS. An effective dose contains about 700–3000 mg of leucine (see Protein — Functions, Quality, and Requirements, Protein Distribution Across the Day). This is why leucine content is a marker of protein quality and why whey (leucine-rich) is effective post-workout (see Protein Powder and Whey).
BCAAs (branched-chain amino acids) — leucine, isoleucine, valine — are sold as a standalone supplement. The evidence is underwhelming: when total protein intake is already adequate, BCAA supplements add little or nothing, because building muscle requires the full set of EAAs, not just three. Leucine alone or BCAAs can transiently raise MPS signaling but cannot sustain net muscle building without the other EAAs. Whole protein or complete EAA blends are superior and usually cheaper per useful gram (see Supplements — A Skeptical Note on Ineffective and Risky Products). BCAAs are largely a redundant product for anyone eating sufficient quality protein.
Key facts
- 9 essential amino acids; EAAs (not non-essential) drive MPS.
- ~10 g EAAs or a 20–40 g protein bolus maximally stimulates MPS.
- Leucine is the trigger (mTOR); effective dose ~700–3000 mg leucine.
- BCAAs (leu/ile/val) add little when total protein is adequate.
- Full EAAs/whole protein beat isolated BCAAs for building muscle.
Connections
- Protein — Functions, Quality, and Requirements — EAAs within total protein needs.
- Protein Distribution Across the Day — leucine threshold per dose.
- Protein Powder and Whey — leucine-rich complete protein.
- Supplements — A Skeptical Note on Ineffective and Risky Products — why BCAAs are usually redundant.
Sources
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Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.