nutrition
Leucine Threshold
The amount of the amino acid leucine per meal (~2–3 g) needed to maximally trigger muscle protein synthesis.
Leucine is the branched-chain amino acid that acts as the primary "on switch" for muscle protein synthesis via the mTOR pathway. Research points to a per-meal leucine threshold of roughly 2–3 g (3–4 g for older adults, who show anabolic resistance) to maximally stimulate the response — equivalent to about 25–35 g of high-quality protein from whey, meat, eggs, or dairy. This is why protein distribution across meals, not just the daily total, matters for muscle retention in a calorie deficit.
Primary Sources
- Norton LE, Layman DK. "Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise." J Nutr. 2006.
- Moore DR et al. "Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men." Am J Clin Nutr. 2009.