Answer: NONE IS ENTIRELY TRUE DISCUSSION: The use of enterocyte-specific fuels is part of a new and potentially exciting phase of “nutritional pharmacology” in parenteral nutrition; however, exciting as the research may be, the use of such fuels is by no means acceptable for indiscriminate use at present. Though some studies have shown that the provision of glutamine in amounts up to 2% in standard parenteral nutrition solutions increases both jejunal and ileal mucosal protein content, cell wall thickness, and DNA content, this has not been the case in all studies, and this reported effect seems very dependent on experimental design. In many of the studies that have shown such an effect, 2% glutamine has been used to replace virtually all nonessential amino acids, probably initiating a deficiency state. The beneficial effects seen with glutamine are far less impressive than those seen with epidermal growth factor, for example, and disappear entirely when a different experimental design is used in which 2% glutamine is added to an adequate amino acid formulation in which glutamine does not replace nonessential amino acids but is added to them. Nonetheless, the use of enterocyte-specific fuels, specifically glutamine, is potentially exciting and should be carefully investigated. More striking are the results that follow massive bowel resection, radiation enteritis, and chemotherapy toxicity. Glutamine may help the small bowel regenerate more quickly, enabling more rapid use of the small bowel for nutrition. It should be pointed out, however, that glutamine is a fuel utilized by many tumors and, thus, one runs the risk of stimulating the growth of the tumor with excessive glutamine. The short-chain fatty acids, produced from bacterial fermentation of soluble pectin, may be useful in both the maintenance of colonocyte-specific nutrition and, in the case of butyrate, ileal enterocyte nutrition