Leucine

Strong mechanistic evidence as the key mTOR activator. Supplementation may benefit elderly or those with low protein intake, but adds little for those consuming adequate protein.

A rough internal score reflecting quantity, quality, and consistency of human evidence. Not a clinical recommendation.

Leucine activates mTORC1 signaling, the primary switch for muscle protein synthesis. A leucine threshold (~2-3 g per meal) maximizes MPS. Studies in elderly show leucine-enriched meals improve MPS rates. In well-fed athletes consuming adequate protein, additional leucine provides minimal extra benefit.

• Primary dietary activator of muscle protein synthesis via mTOR
• Can enhance anabolic response to suboptimal protein meals
• May help preserve muscle mass in elderly populations

2-5 g per meal to maximize muscle protein synthesis. Total daily intake of 8-14 g from diet plus supplements. Most effective with meals containing at least 20 g total protein.

• Generally well-tolerated
• May deplete isoleucine and valine at very high isolated doses
• Rare GI discomfort

High doses may deplete other BCAAs. Not appropriate as sole therapy for sarcopenia without adequate total protein.

Benefits are primarily for those not meeting the leucine threshold per meal (elderly, low-protein diets). Athletes consuming 1.6+ g/kg protein likely get sufficient leucine.

• Muscle60
• Recovery50