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What is isoleucine? Why do we need it?

Isoleucine is an essential amino acid. It belongs to a special group of amino acids called branched-chain amino acids (BCAAs), which are needed to help maintain and repair muscle tissue. Isoleucine also helps prevent muscle proteins from breaking down during exercise.

While there is still some question as to whether isoleucine and other branched-chain amino acids improve exercise performance or enhance the effects of physical training, supplements may be beneficial under certain conditions. Some studies have shown that isoleucine and other BCAAs prevent muscle loss at high altitudes and may prolong physical endurance under extreme heat. People with liver and kidney failure may also benefit from isoleucine supplementation. In addition, a trial published in 1988 found that BCAA supplements help patients with Lou Gehrig’s disease maintain muscle strength; other studies have refuted these findings, however.

How much isoleucine should I take?

The recommended daily dosage of isoleucine and other branched-chain amino acids is 25-65 mg four every 2.2 pounds of body weight. Most diets provide an adequate amount of BCAAs. Competitive athletes sometimes take larger amounts — up to two grams of isoleucine (and 11 grams of BCAAs overall) per day.

What are some good sources of isoleucine? What forms are available?

All protein-containing foods have some amount of isoleucine and other BCAAs. The best sources include red meat and dairy products such as eggs, milk and cheese. Whey protein and egg protein supplements are other good sources. Isoleucine is usually sold in conjunction with other amino acids.

What can happen if I take too much isoleucine? Are there any interactions I should be aware of? What precautions should I take?

Only individuals who are deficient in protein would become deficient in isoleucine. However, since most Western diets provide more than enough protein, isoleucine deficiency is extremely rare. High intake of isoleucine and other BCAAs could cause these substances to be converted into other amino acids (or to fat for storage). Individuals with kidney or liver disease should not consume large amounts of isoleucine or other BCAAs without first contacting a qualified health care practitioner.

At the time of this writing, there are no known drug interactions with isoleucine. As always, make sure to consult with a licensed health care provider before taking isoleucine or any other dietary supplement or herbal remedy.


  • Blomstrand E, Hassmen P, Ekblom B, et al. Administration of branched-chain amino acids during sustained exercise—effects on performance and on plasma concentration of some amino acids. Eur J Appl Physiol 1991;63:83-8.
  • Kelly GS. Sports nutrition: a review of selected nutritional supplements for bodybuilders and strength athletes. Med Rev 1997;2:184-201.
  • Mittleman KD, Ricci MR, Bailey SP. Branched-chain amino acids prolong exercise during heat stress in men and women. Med Sci Sports Exerc 1998;30:83-91.
  • Plaitakis A, Smith J, Mandeli J, et al. Pilot trial of branched-chain amino acids in amyotrophic lateral sclerosis. Lancet 1988;1:1015-8.
  • Schena F, Guerrini F, Tregnaghi P, et al. Branched-chain amino acid supplementation during trekking at high altitude. The effects on loss of body mass, body composition, and muscle power. Eur J Appl Physiol 1992;65:394-8.
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