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What is leucine? Why do we need it?

Leucine 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. Leucine also helps prevent muscle proteins from breaking down during exercise.

While there is still some question as to whether leucine 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 leucine 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 leucine 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 leucine should I take?

The recommended daily dosage of leucine 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 five grams of leucine (and 11 grams of BCAAs overall) per day.

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

All protein-containing foods have some amount of leucine 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. Leucine is usually sold in conjunction with other amino acids.

What can happen if I take too much leucine? 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 leucine. However, since most Western diets provide more than enough protein, leucine deficiency is extremely rare. High intake of leucine 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 leucine or other BCAAs without first contacting a qualified health care practitioner. At the time of this writing, there are no known drug interactions with leucine. As always, make sure to consult with a licensed health care provider before taking leucine or any other dietary supplement or herbal remedy.


  • Blomstrand E, Hassmen P, Ek S, et al. Influence of ingesting a solution of branched-chain amino acids on perceived exertion during exercise. Acta Physiol Scand 1997;159:41-9.
  • 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.
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