Isoleucine is a member of the aliphatic side-chain amino acid family that is composed of hydrophobic biochemicals found primarily in proteins and enzymes. Like several other members of this family (such as valine and leucine), isoleucine is an essential amino acid in human nutrition that is not synthesised by human tissues.
Isoleucine is concentrated in the muscle tissues, and is necessary for haemoglobin formation and for stabilising and regulating blood sugar and energy levels. A deficiency of isoleucine can produce symptoms similar to those of hypoglycemia.
The branched-chain amino acids (BCAA) - isoleucine, leucine and valine - are all suitable for use as supplements for bodybuilding. Both aerobic exercise and strength training increase protein requirements and during aerobic exercise, these amino acids can be used for energy production, providing up to 10% of the total energy produced during long-duration activity. BCAA supplementation may be useful in other performance situations, such as preventing muscle loss at high altitudes, and prolonging endurance performance in high temperatures. Studies also suggest that BCAA supplementation may improve exercise-induced declines in some aspects of mental functioning.
Patients with liver diseases that lead to coma tend to have low concentrations of BCAA’s along with excess levels of certain other amino acids. Preliminary research has suggested that people with this condition may therefore find supplementation with BCAA’s helpful. Therapeutic effects of BCAA’s have also been shown in children with liver failure and adults with cirrhosis of the liver and chronic kidney failure.
One study showed that regular use of BCAA’s by adolescents and young adults with Phenylketonuria (a genetic disease that causes abnormally high amounts of phenylalanine to accumulate in the blood, causing damage to the nervous system), improved performance on some mental functioning tests. This may be due to the fact that BCAA’s compete with phenylalanine, reducing it - and its toxic effects.