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Nutrition

Leucine

An essential amino acid that is the main dietary trigger of muscle protein synthesis.

By the glp1.how editorial teamReviewed

Leucine is an essential branched-chain amino acid (BCAA), so your body can't make it and it has to come from food. It's the main molecular trigger for muscle protein synthesis. A commonly cited target is roughly 2.5–3g of leucine in a meal (the "leucine threshold"), though the evidence for a fixed threshold is mixed. That's why per-meal protein, and not only the daily total, gets attention on a GLP-1.

Animal proteins are the richest sources: whey and dairy, eggs, meat, and fish. Soy and legumes have smaller amounts. When appetite is suppressed and meals are small, hitting the leucine threshold at each meal (through protein-rich foods or a whey supplement) is a practical way to protect lean mass during weight loss. See protein, fat, and carbohydrates on a GLP-1 and the "30g of protein per meal" myth.

A 2021 systematic review found that the leucine-trigger idea best explains muscle-building responses in older adults and after isolated proteins such as whey, and less so in younger adults eating whole foods (Frontiers in Nutrition (external link)).

nutritionproteinamino-acidleucinemuscle-protein-synthesis

Revision history

Updated 2 times since Sep 2, 2026 · show changes
  1. v3

    Body revised

  2. v2

    Body revised

  3. v1

    Change tracking began

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Related terms

  • Muscle protein synthesis · The biological process of building new muscle protein, stimulated by resistance exercise and dietary protein intake.
  • GLP-1 · A gut hormone (glucagon-like peptide-1) that stimulates insulin release, slows digestion, and reduces appetite; the target of drugs like semaglutide and liraglutide.
  • Lean mass · Body weight from everything other than fat: mostly muscle, plus organs and water, and in the broad sense bone. On a DXA report, lean mass usually leaves bone out.

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