Best Leucine for Muscle
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Last reviewed May 2026
Clinical dose: 2000–5000 mg
Why Leucine for Muscle
Leucine plays a supporting role in muscle. Essential branched-chain amino acid (BCAA). Primary activator of mTOR signaling and muscle protein synthesis. In clinical studies, leucine triggers muscle protein synthesis via mTOR activation.
What dose to look for
Clinical studies typically use 2000–5000 mg of leucine. 2–3 g is the 'leucine threshold' for triggering muscle protein synthesis; 5 g common in BCAA blends. Products below this range may not deliver meaningful results.
What the research says
Leucine has strong clinical evidence for muscle benefits. Primary trigger for mTOR-dependent muscle protein synthesis; 2-3g is the threshold for maximal activation Learn more
Clinical research on L-Leucine / BCAAs
MODERATE — Leucine is the key mTOR trigger, but BCAA supplements are redundant if protein intake is adequate · 2.5–5 g leucine/serving; BCAAs typically dosed at 5–10 g (2:1:1 ratio)
- •2017 meta-analysis found BCAA supplementation reduced exercise-induced muscle damage (lower CK levels) and delayed-onset muscle soreness, particularly when taken before resistance exercise. PubMed
- •Leucine is the primary activator of the mTOR pathway — the master regulator of muscle protein synthesis. A leucine threshold of ~2–3 g per meal is required for maximal MPS stimulation.
- •Critical nuance: a 2017 study showed BCAAs alone (without other essential amino acids) cannot sustain muscle protein synthesis — they only stimulate it transiently. Whole protein sources (whey, food) are superior because they provide all EAAs needed for actual muscle building. PubMed
- •BCAAs may have a niche use case: during fasted training or when total protein intake is very low. For anyone consuming adequate protein (1.6+ g/kg/day), BCAA supplementation is likely redundant.