Leucine
Leucine is the essential amino acid that tells muscle to start building protein. Adults need about 39 mg per kilogram of body weight a day, which most protein foods cover easily.
39 mg per kg of body weight a day
2.7 g a day for a 70 kg adult
Upper limit · none set, for lack of studies
- Most per 100 g 3.1g Bacon
- In protein 59mg/g of protein, the WHO pattern
- Main sources Meat, fish and dairy then nuts, seeds and beans
- Type BCAA one of three branched-chain amino acids
Daily requirement: WHO, FAO and UNU 2007. Food figures per 100 g from USDA FoodData Central, only for foods with a Caltide calorie page.
Foods High in Leucine
Ranked per 100 g, with what a usual portion gives, limited to 3 foods per category. Foods with a Caltide calorie page link to it.
B
Bacon
Nutrition facts
3.1g / 100 g
G
Gruyère
3.1g / 100 g
S
Soy nuts
2.7 g in 1 cup
2.9g / 100 g
C
Cube steak
0.81 g in 1 piece/slice
2.7g / 100 g
F
Fontina
2.7g / 100 g
G
Gouda
2.6g / 100 g
T
Tilsit
0.54 g in 1 slice
2.5g / 100 g
B
Beef roast
1.5 g in 1 regular/thin slice
2.5g / 100 g
B
Beef sirloin steak
0.76 g in 1 piece/slice
2.5g / 100 g
M
Maitake mushroom
2.5g / 100 g
P
Pumpkin seeds
3.4 g in 1 cup
2.4g / 100 g
R
Rotisserie chicken breast
1.4 g in 1 medium slice
2.4g / 100 g
What Is Leucine?
Leucine is one of the nine essential amino acids, the ones the body cannot make and has to get from protein in food or from supplements. It is also the most common essential amino acid in most food proteins, so a meal with protein in it almost always brings leucine with it.
Leucine and Muscle Protein Building
Like every amino acid, leucine is built into the body's own proteins. Its second job is unusual: inside muscle cells, a rise in leucine switches on a signal called mTORC1, which starts the machinery that makes new muscle protein. That is why leucine gets more attention from sports nutrition than any other amino acid.
The signal is only a starter. Building muscle still takes all nine essential amino acids, including the other two branched-chain ones, isoleucine and valine. If they are missing, the switch is on but the materials run out.
Where the Body Breaks Down Leucine
Most amino acids are broken down in the liver, but leucine and the other branched-chain amino acids are broken down mainly in muscle. Leucine is also one of only two amino acids, with lysine, that the body cannot turn into glucose: its carbon ends up as ketone bodies or fat, or is burned for energy.
Leucine per Gram of Protein
Foods differ in how much leucine their protein carries, not only in how much protein they have. In the Caltide food library, mozzarella protein has about 113 mg of leucine per gram, cod about 83 mg and black beans about 80 mg, while peanuts have about 63 mg. The WHO pattern for adults is 59 mg per gram, so all of these meet it.
Leucine in a Day of Meals
One ordinary day built only from foods in the Caltide food library, in usual portions, added up per meal. No supplements.
| Meal | Foods | Leucine |
|---|---|---|
| Breakfast | Oats (40 g), Milk (250 g) | 1.2g |
| Lunch | Turkey (90 g), Chickpeas (180 g) | 2.9g |
| Snack | Pistachios (28 g) | 0.45g |
| Dinner | Cod (140 g), Potato (200 g), Broccoli (90 g) | 2.9g |
| Total | 7.5g |
That is 275% of what a 70 kg adult needs. Ordinary eating clears the total with room to spare, but the amount is uneven across meals: breakfast brings less than half of what lunch or dinner does.
Common Leucine Mistakes
Thinking leucine alone builds muscle. It starts the process. Without the other essential amino acids from a full protein, there is little to build with.
Believing plant eaters run short. Beans, lentils and nuts all carry leucine. A plant-based diet with enough total protein covers the requirement; the amino acid plants are more often low in is lysine.
Counting a BCAA drink as protein. A scoop of BCAAs supplies three amino acids out of the nine you need. It is not a substitute for a protein-rich meal.
Leucine Supplements
Supplements are a source of leucine too, sold alone, in blends and inside protein powders.
Leucine Supplement Forms
- L-leucinethe amino acid on its own, as a powder or capsules
- BCAA blendsleucine, isoleucine and valine, most often in a 2:1:1 ratio, so half the powder is leucine
- EAA blends and whey proteinall nine essential amino acids, leucine among them; the label lists its amount per scoop
- HMBa breakdown product of leucine sold on its own; the body makes only about 5% of broken-down leucine into it
What Studies Show About Leucine Supplements
Reviews of human studies find that BCAAs taken alone raise muscle protein building less than a complete protein does. People who already eat enough protein have little reason to add leucine on top.
Sources are listed at the end of this page. Not medical advice.
Tracking Leucine in Caltide
- Logged automaticallyCaltide adds up the leucine in every food you log and, once your weight is set, shows it in the Nutrition tab against the WHO amount for your body weight.
- Supplements count tooAdd your BCAA or protein powder once with its leucine per scoop. Each day you tick it off, it counts toward your total.
Leucine Sources and References
The figures and claims on this page are checked against these sources. Food amounts come from USDA FoodData Central.
Questions About Leucine
About 39 mg per kilogram of body weight, according to the WHO, FAO and UNU 2007 report. That is about 2.7 g a day for a 70 kg adult.
In the Caltide food library, bacon: 3.1 g per 100 g. Gruyère (3.1 g) and Soy nuts (2.9 g) come next.
Leucine switches on mTORC1, the signal inside muscle cells that starts building new protein. It can only start the process: the other eight essential amino acids still have to be there for the muscle to be built.
Not on their own. Reviews of human studies find that branched-chain amino acids alone give a weaker muscle building response than a complete protein such as whey, because the other essential amino acids run short.
HMB (beta-hydroxy beta-methylbutyrate) is a breakdown product of leucine. The body turns only about 5% of the leucine it breaks down into HMB, so it is sold as a separate supplement.
Yes, if you eat enough protein. Chickpeas have 0.63 g per 100 g and black beans 0.7 g, so a 180 g cup of either gives over 1 g, about 40% of what a 70 kg adult needs.
No upper limit has been set for leucine from food or supplements, because studies are too few. People with maple syrup urine disease, a rare inherited disorder, cannot break leucine down and must limit it.
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