Understanding the interplay between food structures, ileum and appetite regulation

Abstract

Evidence suggests that the ileum is an important player in appetite regulation. The ileum contains a high density of L-cells that secrete appetite suppressing hormones Glucagon Like Peptide-1 and Peptide YY (PYY) in response to luminal nutrients and bacterial fermentation products, short chain fatty acid (SCFAs). Processing of foods may change their structures and reduce the amount of carbohydrates reaching the ileum, which may reduce appetite hormone release. However, access to the human ileum is difficult and little is known about the interplay between food, ileum environment and appetite hormone release. This thesis aimed to understand the impact of food structures on the levels of carbohydrate reaching the ileum and their effect on SCFA production and appetite hormone release. A nasoenteric tube was placed in the distal ileum of healthy participants (n=10) who consumed one of the three intervention diets for four days: High fibre, intact structures (I-HF) High fibre, disrupted structures (D-HF) or Low fibre, disrupted structures (LF). Blood and ileal samples were collected on day 4 in fasted and fed states (hourly for 8h). Disrupting the food structures of a high fibre diet (D-HF) reduced the amount of reducing sugars and bile acids, but not starch, in the ileal space compared to a high fibre intact diet (IHF). The numbers of bacteria and the concentrations of SCFAs in the ileum dramatically dropped from fasted to postprandial states, and this effect was not different between the groups. Postprandial PYY release was higher in D-HF in comparison to LF. Metabolomic analysis of ileal contents identified dynamic changes in several metabolites which were different between groups, including aspartate which was higher in D-HF compared to I-HF and LF. In addition, D-HF had higher serum SCFAs compared to I-HF and LF groups. Therefore a difference in ileal metabolites and/or colonic fermentation may be playing a part in the observed PYY difference. Further studies are needed to better understand the role of food structures and ileal metabolites in appetite hormone release.