izoleucin

Isoleucine is an essential amino acid and one of the three branched-chain amino acids (BCAAs), the others being leucine and valine. In humans, it cannot be synthesized endogenously and must be obtained from dietary protein. The L-enantiomer is the biologically active form used in protein synthesis; the D-enantiomer is not utilized by the body.

Biochemical role and metabolism: Isoleucine participates in protein synthesis, tissue repair, and nitrogen balance. It is metabolized primarily in skeletal muscle through branched-chain amino acid transaminases to the corresponding ketoacid, which is further degraded to acetyl-CoA and succinyl-CoA. This makes isoleucine both ketogenic and glucogenic, contributing to energy production and glucose metabolism, especially during prolonged exercise.

Dietary sources and intake: Rich sources include animal proteins such as meat, fish, eggs, and dairy. It is also found in plant proteins such as soy, legumes, nuts, seeds, and whole grains. A balanced diet generally provides sufficient isoleucine; high-dose supplementation is used in certain medical nutrition contexts and some athletic supplements, though intake should be considered in the context of overall amino acid balance.

Clinical and practical notes: Isoleucine deficiency is rare but can occur with severe malnutrition or metabolic disorders. In clinical nutrition, isoleucine is included in standard amino acid formulations. Excessive intake from supplements can disrupt amino acid balance and kidney metabolism, so supplementation should follow appropriate guidance.