Isoleucine

A BCAA with a role in energy production in muscle. In studies it promoted the uptake of glucose into muscle cells.

What isoleucine does in the body

Isoleucine is one of the three branched-chain amino acids (BCAA) and is essential. Unlike most amino acids, it is broken down not first in the liver but mainly in the muscles: an enzyme with vitamin B6 transfers its amino group to alpha-ketoglutarate, and an enzyme complex in the mitochondria that needs vitamins B1, B2, B3, B5 and lipoic acid breaks down the carbon skeleton further. The end products are acetyl-CoA, which supplies energy directly, and propionyl-CoA, which with biotin and vitamin B12 is channelled into energy metabolism or can become glucose. The amino group leaves the muscle as alanine or glutamine. In studies, isoleucine promoted the uptake of glucose into muscle cells. At the blood-brain barrier it shares a transporter with tryptophan, tyrosine and phenylalanine.

Low isoleucine – what happens in the body?

When little isoleucine is available, an essential building block is lacking and protein production is throttled; to meet demand, muscle protein is broken down. Less of this fuel is available to the muscles, and the competing amino acids have easier access at the blood-brain barrier. Low values occur with low protein intake and malnutrition; with advanced liver disease the branched-chain amino acids fall, while the aromatic ones such as phenylalanine and tyrosine rise.

High isoleucine – what happens in the body?

The branched-chain amino acids usually rise together when their breakdown is slowed. In studies, raised values have been observed with insulin resistance, excess weight and type 2 diabetes; the breakdown enzyme complex is less active in fat tissue and the liver, and intermediate breakdown products are suspected of disrupting the transmission of the insulin signal. In the rare inherited maple syrup urine disease this enzyme complex is missing; isoleucine, leucine and valine accumulate markedly and the urine smells of maple syrup – the disorder is detected in newborn screening. Values rise temporarily after protein-rich meals and in the first days of fasting.

The interpretation is given in your report.