L-Leucine (standalone)

Tier 1 — strong evidence · Muscle protein synthesis · mTOR · Sarcopenia · Leucine threshold

The principal nutritional activator of mTORC1, the kinase that triggers skeletal muscle protein synthesis (MPS). A leucine threshold of approximately 2-3 g per meal must be reached to maximally stimulate MPS — protein meals providing less fail to fully activate muscle building regardless of total protein content. Adding 2.5-3 g L-leucine to a low-protein meal in older adults brings MPS to the level of a high-protein meal, a finding replicated in multiple isotope-tracer studies. Particularly important for plant-based eaters (plant proteins contain 30-50% less leucine per gram than animal…

Dose: 2-3 g added to each protein-containing meal or shake; older adults and vegans should target 3-4 g per meal to overcome anabolic resistance and lower plant-protein leucine density.