Leucine Threshold Calculator (Protein per Meal for Muscle Growth)
Find how much protein you need per meal to reach the leucine threshold (about 2.5–3 g) for muscle protein synthesis, by protein source — whey, milk, egg, meat, soy, pea, rice and more.
How it works
Protein per meal (g) = leucine target (g) ÷ leucine fraction of the protein · e.g. 2.5 g ÷ 0.11 = 23 g whey protein
Leucine is the branched-chain amino acid that switches on muscle protein synthesis through the mTOR pathway. Studies feeding graded doses of protein found that about 20–25 g of high-quality protein — roughly 2–2.5 g of leucine — maximally stimulates synthesis in young adults at rest, while older adults need about 0.4 g/kg or ~3 g of leucine per meal because of “anabolic resistance”. Proteins differ in leucine content (dairy is richest, wheat and most plant proteins lower), so the protein dose needed to hit the threshold varies by source. Leucine percentages here are typical values from published amino-acid analyses and food-composition data; branded products vary.
Worked example
With whey protein (≈ 11% leucine) and a 2.5 g leucine target: 2.5 ÷ 0.11 = 22.7, so about 23 g of protein per meal. Over 4 meals that is 91 g of protein and 10 g of leucine per day. Wheat protein would need 2.5 ÷ 0.068 = 37 g per meal.
Sources: Moore DR et al. (2009) Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr 89:161–168 · Gorissen SHM et al. (2018) Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids 50:1685–1695 · Bauer J et al. (2013) PROT-AGE recommendations on optimal dietary protein intake in older people. J Am Med Dir Assoc 14:542–559
Frequently asked questions
What is the leucine threshold?
The amount of leucine in a meal that appears to maximally trigger muscle protein synthesis — about 2–2.5 g for young adults and closer to 3 g for older adults. Below it, the anabolic response to a meal is smaller.
How much protein per meal is that?
About 20–25 g of whey or dairy protein, 25–30 g from eggs, meat or fish, and 30–40 g from most plant proteins. Mixing plant sources, or adding a little extra protein, closes the gap.
Should I take leucine supplements?
Usually not needed. Getting enough total protein spread over 3–5 meals matters more. Free leucine added to a low-protein meal raises synthesis briefly but cannot replace the other essential amino acids.
Does the leucine threshold matter for older adults?
Yes, arguably more. Ageing muscle responds less to small protein doses, so guidelines such as the PROT-AGE group suggest 25–30 g of protein per meal with about 2.5–2.8 g of leucine.
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This calculator gives general nutrition estimates for healthy adults and is not medical advice. People with diabetes, kidney disease, pregnancy or other conditions — and anyone using medication that affects blood sugar — should follow their doctor or dietitian.