Isoleucine
Isoleucine is an essential branched-chain amino acid that muscle can burn for fuel. Adults need about 20 mg per kilogram of body weight a day, 1.4 g for someone weighing 70 kg.
20 mg per kg of body weight a day
1.4 g a day for a 70 kg adult
Upper limit · none set, for lack of studies
- Most per 100 g 1.8g Bacon
- In protein 30mg/g of protein, the WHO pattern
- Main sources Meat, fish and cheese then eggs, nuts 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 Isoleucine
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
1.8g / 100 g
S
Soy nuts
1.6 g in 1 cup
1.7g / 100 g
G
Gruyère
1.6g / 100 g
M
Maitake mushroom
1.6g / 100 g
T
Tilsit
0.31 g in 1 slice
1.5g / 100 g
C
Colby cheese
1.5g / 100 g
C
Cube steak
0.44 g in 1 piece/slice
1.5g / 100 g
V
Veal chop
1.3 g in 1 chop
1.5g / 100 g
C
Colby Jack cheese
1.4g / 100 g
B
Beef sirloin steak
0.42 g in 1 piece/slice
1.4g / 100 g
P
Pumpkin seeds
1.8 g in 1 cup
1.3g / 100 g
P
Pioppini mushroom
1.3g / 100 g
What Is Isoleucine?
Isoleucine is one of the nine essential amino acids and one of the three branched-chain amino acids (BCAAs), with leucine and valine. The body cannot make it, so every gram has to come from protein in food or from supplements.
Isoleucine vs. Leucine
Isoleucine and leucine are isomers: the same atoms, arranged differently, so they have exactly the same weight. The difference shows up when the body breaks them down. Leucine ends up only as material for ketone bodies and fat, while isoleucine splits into two parts, one that can become glucose and one that cannot. That makes isoleucine both a fuel for muscle and, in part, a raw material for glucose.
Like the other branched-chain amino acids, isoleucine is broken down mainly in muscle rather than in the liver. Its main job, though, is the ordinary one: being built into the body's proteins, from muscle fibers to enzymes.
BCAA Ratios in Food
Most BCAA supplements mix leucine, isoleucine and valine 2:1:1. Food protein has its own ratio, with less leucine for each part of isoleucine. The table shows the three in five library foods, per 100 g, with the ratio set to isoleucine as 1.
| Food | Leucine | Isoleucine | Valine | Ratio |
|---|---|---|---|---|
| Egg, boiled | 1.1g | 0.69g | 0.77g | 1.6 : 1 : 1.1 |
| Cod, baked | 1.9g | 1.1g | 1.2g | 1.8 : 1 : 1.1 |
| Mozzarella | 1.8g | 1.1g | 1.3g | 1.6 : 1 : 1.2 |
| Chickpeas, cooked | 0.63g | 0.38g | 0.37g | 1.7 : 1 : 1.0 |
| Oats, dry | 0.98g | 0.5g | 0.69g | 1.9 : 1 : 1.4 |
| Typical BCAA powder | 2 : 1 : 1 |
Across these foods leucine runs 1.6 to 1.9 times isoleucine, and valine runs from level with isoleucine to 1.4 times it in oats. A 2:1:1 powder is not a copy of food protein; it is a choice to weight the mix toward leucine.
How Much Food Gives 1.4 g of Isoleucine
A 70 kg adult needs about 1.4 g of isoleucine a day. One boiled egg of 50 g gives about 0.34 g, a 180 g cup of cooked lentils about 0.7 g, and a 125 g ball of mozzarella about 1.4 g on its own. Anyone eating enough protein from varied foods meets the figure without trying.
When Isoleucine Is a Problem
Shortage from food is rare outside of severe protein malnutrition. The opposite problem is maple syrup urine disease (MSUD), a rare inherited disorder in which the enzyme that breaks down all three branched-chain amino acids does not work. They build up in the blood, the urine smells sweet like maple syrup, and the condition is managed with a special diet low in leucine, isoleucine and valine. A related compound, alloisoleucine, appears in the blood in MSUD and is used to diagnose it.
Isoleucine in Supplements
Supplements are also a source, though isoleucine is almost never sold on its own.
Supplements That Contain Isoleucine
- BCAA blendsusually a quarter of the powder by weight in a 2:1:1 mix, so 5 g of BCAAs carries about 1.25 g of isoleucine
- Essential amino acid blendsall nine essential amino acids; the label lists isoleucine per serving
- Protein powderswhey, casein, soy and pea protein all contain it as part of their protein
What to Know About Isoleucine Supplements
There is no good human evidence for taking isoleucine alone. The three branched-chain amino acids share the same carriers into cells and the same enzymes for breakdown, so a large dose of leucine can lower blood levels of isoleucine and valine.
Sources are listed at the end of this page. Not medical advice.
Tracking Isoleucine in Caltide
- Logged automaticallyCaltide adds up the isoleucine in the foods you log and the supplements you tick off, and once your weight is set shows the day against 20 mg per kilogram in the Nutrition tab.
Isoleucine Sources and References
The figures and claims on this page are checked against these sources. Food amounts come from USDA FoodData Central.
Questions About Isoleucine
About 20 mg per kilogram of body weight, in the WHO, FAO and UNU 2007 report: 1.4 g a day for a 70 kg adult. In protein terms, that is 30 mg of isoleucine per gram of protein.
In the Caltide food library, bacon: 1.8 g per 100 g. Soy nuts (1.7 g) and Gruyère (1.6 g) come next.
No. They have the same atoms in a different arrangement, so they weigh exactly the same, but the body handles them differently. Leucine cannot be turned into glucose; isoleucine can be, in part.
A boiled egg has 0.69 g of isoleucine per 100 g, so one 50 g egg gives about a third of a gram, roughly a quarter of what a 70 kg adult needs in a day.
Almost never. Isoleucine is rarely sold alone; it comes inside BCAA and essential amino acid blends, and protein foods cover the requirement for anyone eating enough protein.
Two parts leucine to one part isoleucine and one part valine, the most common mix in BCAA supplements. Food protein has less leucine relative to the other two, closer to 1.6:1:1.1 in eggs.
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