Glutamine: commercially essential or conditionally essential? A critical appraisal of the human data

Abstract

Glutamine is a nonessential amino acid that can be synthesized from glutamate and glutamic acid by gluta-mate-ammonia ligase. Glutamine is an important fuel source for the small intestine. It was proposed that glutamine is necessary for the maintenance of normal intestinal morphology and function in the absence of luminal nutrients. However, intestinal morphologic and functional changes related to enteral fasting and parenteral nutrition are less significant in humans than in animal models and may not be clinically significant. Therefore, it is unclear whether glutamine is necessary for the preservation of normal intestinal morphology and function in humans during parenteral nutrition. It was suggested that both glutamine-supplemented parenteral nutrition and enteral diets may pre-vent bacterial translocation via the preservation and augmenta-tion of small bowel villus morphology, intestinal permeability, and intestinal immune function. However, it is unclear whether clinically relevant bacterial translocation even occurs in humans, much less whether there is any value in the prevention of such occurrences. Results of the therapeutic use of glutamine in humans at nonphysiologic doses indicate limited efficacy. Although glu-tamine is generally recognized to be safe on the basis of rela tively small studies, side effects in patients receiving home parenteral nutrition and in those with liver-function abnormali-ties have been described. Therefore, on the basis of currently available clinical data, it is inappropriate to recommend gluta-mine for therapeutic use in any condition.