Leucine

Leucine is an essential branched-chain amino acid (BCAA) — one the body can't make, so it has to come from food. It matters because it's the primary molecular trigger for muscle protein synthesis: reaching roughly 2.5–3g of leucine in a meal (often called the "leucine threshold") is what most strongly switches on muscle building — which is why per-meal protein, not just the daily total, gets attention on a GLP-1.

Leucine is richest in animal proteins — whey and dairy, eggs, meat, and fish — and present in smaller amounts in soy and legumes. 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.

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