The impact of food structure and promoting short chain fatty acids production on energy homeostasis and appetite regulation

Abstract

The structural elements within a food, known as food structure, are thought to play a critical role in appetite regulation and energy homeostasis. Food structure can refer to the spatial arrangement of cellular structural elements, such as starch granules, or the physical form of a food. Manipulating the starch structure within a food system, such as in peas, can limit starch digestibility and thus improve the quality of the starch eaten. Bypassing upper gastrointestinal (GI) tract digestion can increase microbiota fermentation activity, which is responsible for the beneficial effects associated with resistant starch consumption. Short-chain fatty acids, fermentation by-products, have previously been reported to regulate glucose homeostasis, reduce energy intake and increase peripheral anorexigenic gut hormone concentrations in humans. A large part of this thesis aimed to investigate the acute effects of manipulating the starch structure within peas by inactivating the starch-branching enzyme of the pea seeds (SBE-deficient peas) on appetite regulation and energy homeostasis in humans. The first study presented in this thesis investigated the effect of food structure within peas on gastric emptying rates using a 13C breath test. The data suggest that manipulating the structure of the peas improves glycaemic response without affecting the gastric emptying rate. The second study presented in this thesis investigated the effect of upper GI digestion on different pea structures. SBE-deficient pea seeds were less available at the small intestinal level to be broken down into glucose. The third study presented in this thesis investigated the effects of lower gut fermentation on different pea structures. SBE-deficient pea seeds produced more short chain fatty acids (SCFAs) as a result of fermentation. However, these pea studies did not cause a change in subjective appetite or in appetite-regulating hormones. Propionate, one of the main SCFAs produced from microbial fermentation, is thought to play a crucial role in appetite regulation and energy homeostasis. Supplementation with inulin-propionate ester (IPE), which selectively enriches colonic propionate, has been reported to increase peripheral anorexigenic gut hormone concentrations and reduce energy intake acutely in humans. Long-term IPE supplementation prevented weight gain and reduced intra-hepatocellular lipid content. Another part of this thesis aimed to investigate the effects of colonic 4 propionate on appetite regulation and energy homeostasis in humans following a lower energy diet through IPE supplementation over a 12-week period. IPE reduced subjective appetite and led to significant weight loss compared to baseline. However, these effects were independent of changes in anorexigenic gut hormones. The majority of the work presented in this thesis supports a role of fermentation in energy and appetite homeostasis. However, the exact underlying mechanisms remain unclear.