Glutamine in Clinical Nutrition

Glutamine was originally considered a nonessential amino acid due the fact that it can be synthesized
from glutamate. Glutamine is also the most abundant amino acid and a major contributor to whole
body nitrogen metabolism in man. However, over several decades, evidence has supported the notion
that glutamine is “conditionally essential” and thus important in human health. For example, glutamine protects the intestinal tract, skeletal muscle, and neuronal tissue against metabolic stress. Some
of the earlier studies showed that reduced intracellular glutamine in muscle was associated with loss
of lean tissue or wasting. This led to the development of nutritional support regimens in which glutamine was administered by enteral or parental routes. However, this is rather a simplistic notion of
glutamine’s role and potential in disease. It is now known that glutamine has an almost ubiquitous
function and is important in maintaining the cellular milieu of virtually every organ in the human
body. Thus, its supplementation not only modulates skeletal muscle mass in postsurgical stress but
also improves lymphocyte count, enhances outcome scores, and ameliorates the peroxidation of lipids
as just a few examples. However, more recent studies have suggested that the administration of glutamine conjugated, or co-administered, with substrates provides greater effi cacy that glutamine alone.
Furthermore the effi cacy of conjugated glutamine is enhanced when administered in complex cocktails that may contain other nutraceuticals. The science of glutamine is thus complex, and fi nding all
the relevant information in a single source has hitherto been problematic. This is however addressed
in Glutamine in Clinical Nutrition .