Title: Digestion in the Upper GI Tract
Funder: Biotechnology and Biological Sciences Research Council

Abstract: The digestion of foods in the upper GI tract is critical for controlling the site and rate of nutrient uptake and post prandial metabolic flux, and the nature of the digesta that enters the lower GI tract and consequential nutrient sensing and gut-brain signalling. The extent of digestion is itself determined by the physical and chemical structural properties of food, including the presence of indigestible materials and structures such as dietary fibre and cell walls. Overconsumption of energy dense foods that are rapidly digested in the upper GI tract leads to high degrees of metabolic flux and a circumvention of homeostatic control measures that regulate food intake. _x000D__x000D_ _x000D__x000D_ This theme will focus on understanding digestive processes in the upper GI tract and the effect of perturbations in food chemical and physical structures. It will use the experimental foods developed in Theme 1 to test a series of hypotheses with the use of in vitro digestion models and in vivo studies. There is a particular focus on examining the properties of starch, fibre and lipids and their interactions with digestive enzymes and bile salts in the upper GI tract._x000D__x000D_ _x000D__x000D_ A range of physico-chemical characteristics are reported to influence starch susceptibility to digestion, however it is still not clear which characteristics have the greatest effects on digestion kinetics, particularly following further hydrothermal and/or mechanical processing. Wild type and mutant lines of peas, barley and wheat will be used to investigate how starch molecular structure affects intrinsic susceptibility to pancreatic a-amylase and in vitro simulated digestion. In vitro digestibility studies will also include analysis of starch entrapped within a fibre (i.e. cell wall) matrix, which occurs naturally within cooked pulses and other plant-based foods. The interactions between fibre and lipids is also of interest with regard to effects on digestion, transport and metabolism of lipids, bile salts and lipophilic nutrients._x000D__x000D_ _x000D__x000D_ In vitro work will be complemented by in vivo studies to gain insight into changes to food structure in the upper GI tract. These human studies will involve intubation of the upper GI tract to sample the food matrices as they are processed in the stomach, and chyme as it passes from the stomach into the duodenum, and the ileal digesta. Our recent studies have indicated that the role of microbiota in the duodenum may have been underestimated, and we will also use nasogastric intubation to sample the gastric, duodenal and ileal microbiota. This will provide new insight into the metabolic activity of this microbial community, which may be of critical significance in generating metabolic products for stimulating the neuroendocrine system and blood hormone release. A dietary intervention study with ileostomy patients will provide for further quantification of the physical nature (at a series of length scales) and the chemical composition of the digesta as it enters the colon. Taken together, these studies will integrate temporal digestive processes within the GI tract with metabolic changes in glucose, lipids and hormones within the systemic circulation.


Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS;2.2 FACTORS RELATING TO PHYSICAL ENVIRONMENT
Health categories: ORAL AND GASTROINTESTINAL