A focus on leucine in the nutritional regulation of human skeletal muscle metabolism in ageing, exercise and unloading states.
Level 5 - mechanism / opinion, no new human data
Narrative review of physiology and mechanism without systematic review methodology
PubMed 37625315 · doi:10.1016/j.clnu.2023.08.010
What was done
Narrative review evaluating the mechanistic and metabolic effects of leucine supplementation—consumed alone or enriched in dietary protein or essential amino acid (EAA) mixtures—on muscle protein synthesis (MPS) and breakdown (MPB) during exercise, aging, and physical inactivity/unloading states.
What was found
Leucine is the most potent EAA stimulator of mechanistic target of rapamycin complex 1 (mTORC1) signaling, increasing phosphorylation of mTORC1 substrates approximately 3-fold more than all other EAAs combined. Exercise extends muscle sensitivity to EAAs and delays the "muscle full" set-point for ~48 hours, whereas aging and inactivity cause a premature muscle full state. Low doses of leucine-enriched protein/EAAs are reported to achieve maximal MPS stimulation without requiring larger total protein doses.
Why it matters
Highlights the mechanistic rationale for targeted leucine enrichment to maximize skeletal muscle anabolism and mitigate muscle wasting associated with aging and physical inactivity.
Limits
As a narrative review, it lacks systematic search criteria, quality appraisal of included studies, and quantitative meta-analytic pooling. Specific clinical outcome metrics (e.g., muscle mass, strength, or functional changes over time) are not reported in the abstract.
Cited by
- supports Consuming red meat, lamb, and eggs stimulates the mTOR pathway due to specific amino acids they contain.