Leucine

ID: leucine

Aliases: L-leucine, branched-chain amino acid, BCAA

Type: compound

Route/form: oral food amino acid or supplement

Status: food_or_supplement

Evidence level: human RCT

Best data tier: human controlled/review

Support scope: human, review/regulatory

Source types: meta_analysis, review, systematic_review

Linked sources: 4

Broad outcomes: Muscle growth / performance / recovery, mTORC / autophagy / nutrient signaling

Reading note: These are curation notes anchored to linked sources, not a clinical recommendation or protocol.

Targets / mechanism

• amino-acid sensing and mTORC1 activation
• muscle protein synthesis trigger hypothesis
• essential amino acid substrate signaling

Optimization domains

• mTORC1
• muscle
• muscle protein synthesis
• sarcopenia
• nutrition
• exercise performance
• recovery

Research basis

• Leucine is the cleanest nutrient-side mTORC1 entry: it is a direct amino-acid signal for post-prandial muscle protein synthesis rather than a drug-like endocrine intervention.
• Systematic reviews support a real leucine-trigger/MPS rationale, especially in older adults and lower-quality protein contexts.
• It helps interpret protein, HMB, EAA, and resistance-training entries because many ?mTOR activation? supplement claims reduce back to leucine/EAA sufficiency.

Limits, risks, and missing evidence

• Isolated leucine is not equivalent to adequate total protein, essential amino acids, training stimulus, sleep, or energy balance.
• Lean-mass and strength effects are context dependent and often modest, especially when total protein is already adequate.
• Chasing mTORC1 activation as a standalone goal can conflict with longevity/autophagy narratives; timing and context matter.

Risk flags

• context dependent
• protein intake ceiling
• not drug like
• mTORC context specific

Linked papers, labels, and reviews

1. Evaluating the Leucine Trigger Hypothesis to Explain the Post-prandial Regulation of Muscle Protein Synthesis in Young and Older Adults: A Systematic Review
   systematic_review / pubmed_leucine_trigger_review_2021
   Systematic review of the leucine-trigger hypothesis for post-prandial muscle protein synthesis; important for mTORC1 activation claims.
2. The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: a systematic review and meta-analysis
   meta_analysis / pubmed_leucine_older_meta_2015
   Older-adult meta-analysis separating acute MPS effects from lean-mass accretion; useful for why leucine is plausible but bounded.
3. Effects of leucine-rich protein supplements in older adults with sarcopenia: A systematic review and meta-analysis of randomized controlled trials
   meta_analysis / pubmed_leucine_sarcopenia_meta_2022
   RCT meta-analysis in sarcopenic older adults; relevant to leucine-rich protein rather than isolated leucine as a drug-like anabolic.
4. International Society of Sports Nutrition Position Stand: protein and exercise
   review / pubmed_issn_protein_position_2017
   ISSN position stand summarizing protein intake, timing, quality, and exercise-adaptation evidence.