Nutrient glossary
What is leucine?
Leucine is the amino acid that flips the muscle-building switch (mTOR), making it the most watched of the nine essentials.
Reviewed 20 July 2026. General information, not medical advice.
The short version
Leucine does something the other amino acids do not: beyond being a building block, it directly signals muscle cells to start synthesising protein. Research on doses suggests roughly 2 to 3 g of leucine in a meal maximises that signal, which a chicken breast, a tin of tuna or a big serving of Greek yogurt reaches.
Dairy is especially rich (whey earned its gym reputation honestly), with meat, fish, eggs, soy and lentils behind it.
Daily reference
2.9 g a day
The adult requirement is about 39 mg per kg of body weight a day; people training for muscle often aim to hit a 2 to 3 g leucine threshold in main meals.
This is the fixed adult reference used across these pages. In the app, your amount adjusts to your body and way of eating.
Best food sources of leucine
| Food | Per serving | Per 100g |
|---|---|---|
| Chicken Breast | 4.16 g | 2.45 g |
| Ribeye Steak | 3.66 g | 2.44 g |
| Sirloin Steak | 3.51 g | 2.34 g |
| Duck Breast | 3.23 g | 2.31 g |
| Roast Chicken | 3.04 g | 2.17 g |
| Tuna Steak | 2.95 g | 2.27 g |
| Halibut | 2.88 g | 2.06 g |
| Pork Chop | 2.86 g | 2.2 g |
Common questions
- How much leucine triggers muscle protein synthesis?
- Around 2 to 3 g in one sitting maximises the signal in most research, roughly the leucine in 25 to 30 g of quality protein.
- What plant foods are high in leucine?
- Soybeans, tofu, tempeh, lentils, peanuts and pumpkin seeds carry the most; larger portions close the gap with animal protein.