Answer: b Glutamine is the most studied gut-specific nutrient. Glutamine has been classified as a nonessential or nutritionally dispensable amino acid since glutamine can be synthesized in adequate quantities from other amino acids and precursors. Glutamine is not included in most nutritional formulas and has been eliminated from TPN solutions because of its relative instability and short half life compared to other amino acids. With few exceptions, glutamine is present in oral enteral diets but only at relatively low levels characteristic of the concentration in most animal and plant stores (about 7% of total amino acids). Several recent studies, however, have demonstrated that glutamine may be an essential amino acid during critical illness, particularly as it relates to supporting the metabolic requirements of the intestinal mucosa. These studies demonstrate that dietary glutamine is not required during states of health but appears to be beneficial when glutamine depletion is severe and/or when intestinal mucosa is damaged by insults such as chemotherapy or radiation therapy. The addition of glutamine to enteral diet reduces the incidence of gut translocation but these improvements are dependent upon the amount of supplemental glutamine and the type of insult studied. Glutamine-enriched TPN partially attenuates villous atrophy that develops during parenteral nutrition. The use of intravenous glutamine in patients appears to be safe and effective in its ability to maintain muscle glutamine stores and improve nitrogen balance. In contrast to glutamine, short chain fatty acids are primary energy source for colonocytes