Leucine-enriched nutrients and the regulation of mammalian target of rapamycin signalling and human skeletal muscle protein synthesis.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing mechanistic and clinical studies without systematic review methodology.
PubMed 18403916 · doi:10.1097/MCO.0b013e3282fa17fb
What was done
This narrative review synthesized recent literature evaluating the cellular signaling pathways—particularly mammalian target of rapamycin (mTOR)—through which leucine and essential amino acids stimulate skeletal muscle protein synthesis in humans, both at rest, with aging, and after resistance exercise.
What was found
The abstract reports no numerical values or statistical effect sizes. It qualitatively reports that leucine-enriched essential amino acid ingestion rapidly activates mTOR signaling and muscle protein synthesis in humans, that post-exercise ingestion enhances this response, and that adding leucine to meals may improve protein synthesis responsiveness in older muscle. It also notes potential involvement of upstream kinases such as hVps34 and MAP43K in leucine sensing.
Why it matters
It outlines the physiological and molecular framework supporting leucine supplementation as a targeted nutritional strategy to preserve muscle mass in conditions characterized by muscle wasting or anabolic resistance.
Limits
As an unsystematic narrative review, study selection and reporting are subject to author bias. The abstract provides no primary data, effect sizes, or participant numbers, and notes that the exact sensing mechanisms linking leucine to mTOR activation in human muscle cells were not yet fully resolved.
Cited by
- supports Leucine activates mTOR more strongly than other amino acids.