Leucine
Also known as L-leucine, Leu
Leucine is an essential amino acid and the most anabolic of the three branched-chain amino acids. The body cannot make it, so it must come from food, and it is the key signal that switches on muscle protein synthesis.
Why it matters
What it does in your body
- Muscle protein synthesis
- Triggers the mTOR pathway that builds muscle
- Branched-chain amino acid used for energy
- Supports recovery and tissue repair
Intake guidance
How much you need
The IOM sets the requirement at 42 mg/kg/day, about 2.9 g/day for a 70 kg adult. Any diet with enough total protein provides plenty.
What affects it
What affects your intake
Total protein intake
Meeting protein needs covers leucine easily, as it is one of the most common amino acids in food protein.
Resistance training and aging
Older adults and lifters may benefit from getting enough leucine per meal to maximize muscle building, roughly 2 to 3 g.
Protein source and distribution
Animal proteins and whey are especially leucine-rich, and spreading protein across meals helps hit the per-meal threshold.
In practice
Good to know
Deficiency is essentially unheard of in people eating enough protein. Leucine and BCAA supplements are popular with athletes because leucine strongly triggers muscle building, and getting about 2 to 3 g of leucine per meal may help older adults counter age-related muscle loss. That said, a complete protein food or shake usually delivers this without a separate supplement.
Where to get it
Best food sources
The bottom line
Leucine is the muscle-building trigger, and a protein-rich meal already supplies plenty. Focus on hitting your total protein rather than buying isolated leucine.
Track leucine automatically
Leucine is one of the 92 nutrients Vora reads from a photo of your meal, so you can see where you stand without weighing or logging by hand.
Sources and method
The classification, roles, and guidance on this page come from the references below, drawing on the Institute of Medicine (now the National Academies) Dietary Reference Intakes and reputable nutrition science.
- Institute of Medicine (2005), Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids
This page is for general education, not medical advice. Reference intakes are population averages for healthy people and do not replace guidance from your doctor or a registered dietitian, especially if you are pregnant, managing a health condition, or considering supplements.