Nonessential Micronutrient



Isoleucine is an essential branched-chain amino acid (BCAA). A building block of protein (as are all amino acids), isoleucine plays a vital role in protein synthesis, muscle building, and preventing muscle loss.

Where to find Isoleucine

Isoleucine is found in most protein-rich foods, particularly meats, fish, cheese, and most seeds and nuts.
Popup: Foods highest in Isoleucine


Why athletes use Isoleucine

Isoleucine, like all BCAA’s, is used by athletes whose muscles are excessively stressed by overtraining to promote healing of injured tissues, speed recovery, protect against muscle-tissue breakdown, and possibly increase lean mass.

Ways that Isoleucine can enhance Muscle Gain & Recovery:
  • Maintain protein balance to promote muscle growth and healing
  • Prevent muscle breakdown and loss, and promote healing of tissues after trauma
Ways that Isoleucine can enhance Energy & Endurance:
  • Stabilize blood sugar to regulate energy levels


Signs of Isoleucine deficiency

Deficiency produces symptoms similar to hypoglycemia

Potential uses for Isoleucine

Research indicates that Isoleucine may be useful in the treatment of:

  • Overtraining
  • Wounds/injuries
  • Stress
  • Liver disorders
  • Catabolism (muscle wasting)
  • Tremors


More about Isoleucine

Isoleucine is an essential (meaning the body cannot make it) amino acid that, along with valine and leucine, is one of the branched-chain amino acids. These three amino acids account for one third of all the protein in muscle tissue, and this significant contribution makes them highly important for helping build muscle and increase energy in muscle cells. They are also converted to other amino acids when deficiencies arise.
The branched-chain amino acids are important for protein synthesis, muscle building, and preventing muscle loss. Quite simply, without branched-chain amino acids, your muscle cells won’t heal or grow.
Recent research has even shown that the three branch-chained amino acids together can reduce muscle wasting (at least slightly) even in people who are bed-ridden.

Why we need it

Found in proteins, isoleucine is needed for the formation of hemoglobin, which carries iron in the blood, and for the regulation of blood sugar, which is burned for energy in the muscles during exercise. In addition, isoleucine is used as fuel by muscle cells and may spare other amino acids from being burned. Researchers theorize that muscle wasting in the elderly is due partially to a deficiency in isoleucine.

In conclusion

While isoleucine is an important amino acid, it doesn’t quite rank up there with the other branched-chain amino acids. Nonetheless, it does have a prominent role in muscle metabolism.



Some athletes choose to get their isoleucine from a quality whey protein powder. Others supplement with between 200 and 2,000 mg per day.
The branched-chain amino acids (BCAA) are often supplemented together — 5 grams of leucine, 4 grams of valine, and 2 grams of isoleucine per day is common, although the amounts needed can vary depending on the person’s weight.


Isoleucine is supplemented on an empty stomach with the other branched-chain amino acids in two divided dosages — one a half hour before training and then another before sleep because of their potential to stimulate the release of growth hormone.

Synergists of Isoleucine

Valine, leucine, and isoleucine, the trio known as the “branched-chain amino acids,” support each others’ effects.

Toxicity of Isoleucine

No known toxicity.

Bans and restrictions

None reported.


  • Blomstrand, E., et al., “Influence of Ingesting a Solution of Branched-Chain Amino Acids on Perceived Exertion During Exercise,” Acta Physiol Scand 159.1 (1997) : 41-9.
  • MacLean, D.A., and Graham, T.E., “Branched-Chain Amino Acid Supplementation Augments Plasma Ammonia Responses During Exercise in Humans,” J Appl Physiol 74.6 (1993) : 2711-7.
  • Stein, T.P., “Branched-Chain Amino Acid Supplementation During Bed Rest: Effect on Recovery,” J Appl Physiol 94 (2003) : 1345-52.