Leucine

Description

Leucine is an essential amino acid. This means it must be obtained through the diet in adequate quantities to meet the body's needs.

Leucine is a member of the branched-chain amino acid family, along with valine and isoleucine. The three branched-chain amino acids constitute approximately 70 percent of the amino acids in the body proteins. As such, their value in the formation and maintenance of structural and functional integrity in humans is unmeasured.

During times of starvation, stress, infection, or recovery from trauma, the body mobilizes leucine as a source for gluconeogenesis (the synthesis of blood sugar in the liver) to aid in the healing process.

It has recently been suggested leucine may have beneficial therapeutic effects on the prevention of protein wasting, as it occurs during starvation, semi-starvation, trauma, or recovery after surgery. Insulin deficiency is known to result in poor utilization of leucine; therefore, individuals who suffer from glucose intolerance may require higher levels of leucine intake. It has also been recently suggested leucine has anabolic effects, thereby preventing muscle protein breakdown and stimulating muscle protein synthesis. Therapeutic use of leucine occurs at doses between 500 and 1,000mg per day.

Recommended Dietary Allowances

The RDA level of leucine has been established as 62mg per day for women and 110mg per day for men.

Food Sources

Foods high in leucine include:

Cottage cheese - dry	4,500 mg/cup
Cottage cheese - creamed	3,294 mg/cup
Fish and other seafoods	1,000-10,000 mg/lb.
Meats	2,000-8,500 mg/lb.
Poultry	3,500-8,500 mg/lb.
Peanuts, roasted with skin	4,500 mg/cup
Sesame seeds	3,500 mg/cup
Dry, whole lentils	3,500 mg/cup

Method of Action

Faulty leucine metabolism can lead to maple syrup urine disease. This is generally seen in infants and can result in retardation. This is a very rare condition, however, and is not a general concern as it relates to leucine supplementation. Leucine supplementation should not be employed in these individuals.

Degradation of the branched-chain amino acids creates a series of branched fatty acid starter pieces, whose utilization leads to the formation of fatty acids that can be incorporated into complex phospholipids. The branched-chain amino acids have a unique muscle-sparing ability due to their gluconeogenic activity.

Abstracts

References

Adibi, S.A., Peterson, J.A. & Kryzysik, B.A. Modulation of Leucine Transaminase Activity by Dietary Means. Am. J. Physiol., 228:432-5, 1975.

Blackburn, G.L., Grant, J.P., Young, V.R., ed. Amino Acids Metabolism and Medical Applications.

Meikle, A.W. & Klain, G.J. Effect of Fasting and Fasting-Refeeding on Conversion of Leucine into Co2 and Lipis in Rat. Am. J. Physiol., 222:1246-50, 1972.

Munro, H.N. & Crim, M.C. The Proteins and Amino Acids. Modern Nutrition in Health and Disease, eds. R.S. Goodhart & M.E. Shils, 6 ed. Philadelphia: Lea and Febiger, 1980.

Swendseid, M.E., Villalobos, J., Figueroa, W.S., and Drenick, E.J., "The Effects of Test Doses of Leucine, Isoleucine or Valine on Plasma Amino Acid Levels--The Unique Effect of Leucine. Am. J. Clin. Nutr., 17:317-21, 1965.

Young, V.R., Meguid, M., Meredith, D.E. & Bier, D.M. Recent Developments in Knowledge of Human Amino Acid Requirements. Nitrogen Metabolism in Man. eds: J.C. Waterlow & J.M.L. Stephen. London: Applied Science Pubs. 1981.