The effects of branched-chain amino acids on muscle protein synthesis, muscle protein breakdown and associated molecular signalling responses in humans: an update.
Level 5 - mechanism / opinion, no new human data
Narrative review without systematic search or meta-analysis
PubMed 37681443 · doi:10.1017/S0954422423000197
What was done
This narrative review evaluated human studies examining the effects of branched-chain amino acid (BCAA: leucine, isoleucine, valine) ingestion on mechanistic target of rapamycin (mTOR) signaling pathways, muscle protein breakdown (MPB), and muscle protein synthesis (MPS) both at rest and during recovery from resistance exercise.
What was found
No quantitative effect sizes or numerical values were reported in the abstract. Qualitatively, BCAA provision (especially leucine) increases phosphorylation of proteins in the mTOR signaling pathway and suppresses whole-body protein breakdown and MPB. While early research showed no standalone effect on MPS, recent trials demonstrate that BCAAs can stimulate resting postprandial MPS and enhance exercise-induced MPS. However, the MPS response to BCAAs alone remains inferior to the response seen with intact, complete protein sources supplying all indispensable amino acids.
Why it matters
It clarifies that standalone BCAA supplementation is suboptimal compared to whole protein sources for stimulating skeletal muscle protein synthesis, despite activating upstream anabolic signaling pathways.
Limits
The abstract provides no numerical data, effect sizes, or study count. As a narrative review, it lacks predefined systematic search criteria and formal quality appraisal. The reviewed literature focuses primarily on acute metabolic and molecular surrogate endpoints rather than long-term gains in muscle mass or strength.
Cited by
- supports Leucine triggers muscle growth signaling.