Isoleucine is an essential amino acid. This means it must be obtained through the diet in adequate quantities to meet the body's needs.
Isoleucine is a member of the branched-chain amino acid family. The three branched-chain amino acids--isoleucine, leucine, and valine--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.
Therapeutic doses of isoleucine may be very helpful in preventing muscle wasting and promoting tissue repair after surgery or trauma. Substantial evidence in the literature supports the anabolic effects of branched-chain amino acids on muscle protein synthesis.
Supplementation with isoleucine may, therefore, have a positive effect on increasing muscle protein in those who are suffering from muscle protein loss.
Amen and Yoshumira have presented evidence which indicates isoleucine, leucine, and valine are important for stimulating anabolic function in humans.
Isoleucine is also converted in the liver to blood sugar; therefore, it can be helpful in maintaining proper blood glucose levels. Therapeutic doses of isoleucine range between 200 and 2,000mg per day.
Recommended Dietary Allowances
The RDA level of isoleucine has been established as 45mg per day for women and 70mg per day for men.
Foods high in isoleucine include:
Cottage cheese - dry 2,475 mg/cup Cottage cheese - creamed 1,769 mg/cup Fish and other seafoods 4,000-6,000 mg/lb. Meats 1,500-6,000 mg/lb. Poultry 2,000-4,500 mg/lb. Peanuts, roasted with skin 3,000 mg/cup Sesame seeds 2,000 mg/cup Dry, whole lentils 2,500 mg/cup
Method of Action
An inborn error in isoleucine metabolism effecting a very small percentage of people can result in the buildup of metabolites in the urine, resulting in what is called "maple syrup urine disease". This condition can be evaluated in infants who may be susceptible to this genetic metabolism disorder. Isoleucine supplementation should not be applied to 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.
Blackburn, G.L., Grant, J.P., Young, V.R., ed. Amino Acids Metabolism and Medical Applications.
Johnson, D.J. & Anderson, G.H. The Prediction of Plasma Amino Acid Concentration from Diet Amino Acid Content. Am J Physiol, 1982.
Morgan, M.Y. Milson, J.P. & Sherlock, S. Plasma Ratio of Valine, Leucine and Isoleucine to Phenylalanine and Tyrosine in Liver Disease. Gut, 19:1068-73, 1978.
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.
Pardridge, W.M. & Oldendorf, W.H. Kinetic Analysis of Blood-Brain Barrier Transport of Amino Acids", Biochim. Biophys. Acta, 401:128-36, 1975.
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.