The trophic effects of substrate, insulin, and the route of administration on protein synthesis and the preservation of small bowel mucosal mass in large mammals.

BACKGROUND & AIMS: We reviewed the literature that has specifically investigated the effects of nutritional support on the preservation of small bowel mucosal mass in humans or large mammals.

METHODS: We searched various databases (up to March 2009) for experimental studies which addressed intestinal protein metabolism of living organisms (humans or large mammals).

RESULTS: In adults, luminal proteins are of central importance for maintaining the intestinal protein content most likely by stimulating protein synthesis. With exclusive total parenteral nutrition, the small intestinal protein content can be largely preserved in humans over prolonged periods of time (1-2 months). To do so, amino acids are of central importance. Carbohydrates are presumably less important for the preservation of gut protein and may be even detrimental. Preponderant carbohydrate feeding may cause a relative intestinal protein deficit in the presence of insufficient luminal protein or parenteral amino acid supply.

CONCLUSION: These findings may explain why a selective inadequate protein intake impairs intestinal function more than a balanced insufficient calorie supply. However, most of the substrate-gut interactions have been examined in healthy or mostly healthy organisms. Corresponding regulatory mechanisms in severely ill or malnourished individuals require further studies to test the hypotheses described above.