Glutamine: metabolism and application in nutrition support.

Glutamine is the most abundant free amino acid in the body. It is avidly consumed by rapidly dividing cells, such as those lining the gut, because its 5-carbon skeleton can provide energy whilst the nitrogen molecules support the synthesis of nucleic acids. Patients who are maintained using conventional solutions of parenteral nutrients become depleted in glutamine, which has led to the reclassification of glutamine as a conditionally essential nutrient. Unfortunately, glutamine is unstable in solution and produces toxic byproducts on decomposition. This means that solutions of nutrients containing glutamine have a relatively short half-life, which has led to the commercialisation of stable dipeptides containing glutamine. Although it is evident that glutamine enhances nitrogen metabolism, there is a lack of consistent evidence from the initial clinical trials demonstrating that supplementation with glutamine has specific clinical advantages. The next few years will witness the performance of larger scale clinical trials and the results of these studies should define a more certain role for glutamine in routine clinical practice.