Leucine Threshold Calculator
Leucine is the primary amino acid responsible for triggering muscle protein synthesis (MPS) via the mTORC1 signalling pathway. A meal must exceed the leucine threshold - the minimum leucine dose that maximally activates MPS - to produce a full anabolic response. Meals containing less than the threshold amount of leucine still contribute amino acids for repair but fail to fully stimulate new muscle protein synthesis. This calculator estimates the leucine threshold dose per meal based on body weight and age group, and then calculates the amount of various common protein sources needed to meet that threshold, helping you plan meals that consistently reach the leucine threshold for optimal muscle building and maintenance.
Leucine threshold formula
Leucine threshold (g) = Body weight (kg) x Leucine factor (0.05 young / 0.07 older)
Whey needed (g) = Leucine threshold / 0.107 (leucine fraction in whey protein)
Chicken breast (g cooked) = Leucine threshold / 0.024 (leucine per g cooked chicken)
Eggs (whole large) = Leucine threshold / 0.54 (leucine per whole egg approx 0.54g)
Frequently asked questions
What is the leucine threshold?
The leucine threshold is the minimum amount of leucine needed in a single meal to maximally stimulate muscle protein synthesis (MPS). Below this threshold, MPS is sub-maximally activated. Research suggests approximately 0.05 to 0.06 g of leucine per kg body weight per meal maximally stimulates MPS in younger adults.
Why is leucine the key amino acid for MPS?
Leucine is a branched-chain amino acid (BCAA) that acts as a nutrient-signalling molecule, activating the mTORC1 pathway that drives muscle protein synthesis. It is the primary amino acid regulating anabolic signalling, not merely a building block.
How much leucine is in common protein sources?
Per 100g of protein: whey protein contains approximately 10 to 11g leucine; chicken breast 7.5g; beef 8g; eggs 8.5g; milk protein 9.5g; soy protein 7.8g. This means 25g of whey provides approximately 2.5 to 2.75g of leucine.
Does leucine requirement increase with age?
Yes. Older adults (above 65) have anabolic resistance: the muscle protein synthesis response to a given leucine dose is blunted. Research suggests older adults may need 40 to 60% more leucine per meal to achieve the same MPS response as younger adults.
Can I take leucine supplements on top of food?
Leucine supplements (or BCAA supplements) added to a meal can help older adults or those eating lower-quality proteins exceed the leucine threshold. However, if meals already contain sufficient high-quality protein with adequate leucine, supplemental leucine does not provide additional benefit.
Official sources
- National Institutes of Health - Office of Dietary Supplements: NIH Dietary Supplements Fact Sheets.
- USDA FoodData Central: USDA Nutrient Database.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.