Glutamine: is it a conditionally required nutrient for the human gastrointestinal system?

Glutamine is a nonessential amino acid which can be synthesized from glutamate and glutamic acid by glutamine synthetase. It is the preferred fuel for the rat small intestine. Animal studies have suggested both glutamine-supplemented parenteral nutrition and enteral diets may prevent bacterial translocation. This effect is thought to be modulated via the preservation and augmentation of small bowel villus morphology, intestinal permeability and intestinal immune function. The existing data are less compelling in humans. It remains unclear what, if any, intestinal deficits actually occur in humans during provision of exclusive parental nutrition. Furthermore, the clinical significance of these changes is largely undefined in humans. The existing data on the use of parenteral and enteral glutamine for the purpose of preserving intestinal morphology and function, and the prevention of bacterial translocation in humans are reviewed. Pertinent animal data are also described.