The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

Contributions of gut functions to the regulation of food intake in humans (#162)

Christine Feinle-Bisset 1
  1. University of Adelaide Discipline of Medicine and NHMRC Centre of Research Excellence in Translating Nutritional Science to Good Health, Adelaide, SA, Australia

As the first point of contact for ingested nutrients, the upper gastrointestinal (GI) tract plays a key role in sensing the characteristics of the ingested meal content and in signaling this information to the brain. The interaction of nutrients with small intestinal nutrient-sensing receptors also triggers the release of gut hormones and initiates feedback loops that lead to adjustments in the rate of gastric emptying, both of which are involved in the regulation of energy intake. Lipid has potent effects on these GI functions, requiring fat digestion and fatty acids with a chain length of ≥12 carbon atoms. Dietary modifications can influence these effects of fat, so that overconsumption of a high-energy, high-fat diet reduces, while energy restriction enhances, sensitivity to the GI and appetite-suppressant effects of fat. Obesity is associated with compromised GI responses to dietary fat, particularly the release of gut hormones, with recent research indicating that this is due, at least in part, to a reduced number of enteroendocrine cells, changes that can be reversed by obesity surgery. Dietary protein, particularly whey, is also a highly satiating macronutrient, in part, mediated by changes in GI functions, although the GI effects of protein appear to be less potent than those of lipid.  In contrast to lipid, the appetite-suppressant effects of protein appear to remain intact in obesity, consistent with the efficacy of high-protein diets to achieve significant weight loss. Interestingly, our recent research, investigating the potential role of amino acids in mediating the effects of protein on GI functions and energy intake, has established that certain amino acids, e.g. L-tryptophan or L-leucine, suppress subsequent energy intake, in excess of their own energy content, despite diverse effects on GI functions, with the effect on energy intake more closely related to their respective plasma concentrations, suggesting that the energy intake-suppressant effects of these amino acids, and protein, may be mediated not primarily by GI effects, but through effects of circulating amino acids.  Taken together, the role of the gut in mediating the energy intake-suppressant effects of dietary nutrients appears to vary according to macronutrient class.  Moreover, the adaptive changes in GI function that occur in response to a high fat intake may, at least in part, underlie the obesogenic properties of fat. Much more research is required to establish whether, and how, specific dietary nutrients can be utilized in the management of obesity and associated comorbidities.