The Library Brands All Products for Encyclopedia Health Concerns Vitamins, Minerals, etc. Leucine is an essential amino acid . Leucine inhibits the breakdown of muscle proteins that may occur after trauma or severe stress. 1 Leucine supplements or protein powders that contain leucine are used by some bodybuilders and other athletes to promote muscle recovery, although it has not produced significant changes in body composition. 2 Phenylketonuria should only be treated under the care of a nutritionally oriented physician.
Leucine is present in all protein foods, such as meat, fish, eggs, milk, and beans.
It is also found in soy protein, whey protein, and other protein supplements. Since all protein foods are good sources of leucine, only an individual deficient in protein would become deficient in leucine. A strict vegetarian or vegan diet, without adequate soy or other protein sources, might be inadequate in its content of leucine, though most American vegan diets are not leucine deficient. To influence protein metabolism and muscles, several grams of leucine are generally taken. No consistent evidence of toxicity has been linked to leucine supplements.