Gastrointestinal transit, appetite and food intake: the role of dietary fat

peer-reviewed A high intake of dietary fat has long been implicated in aetiology of obesity, coronary-heart disease and type 2 diabetes mellitus. Fat is the most potent regulator of gastric emptying (progression of food from the stomach to the small intestine). Chronic exposure to fat may cause alterations to the gastrointestinal tract and hence led to down-regulation of the appetite control system. In this thesis, GE was assessed using the 13C octanoic acid breath test in a healthy adult cohort. Acute pharmacological and nutritional models demonstrated that 10 mg domperidone and 3 g cinnamon respectively, had no effect on gastric emptying rate or appetite responses to a high-fat meal. Also detailed in this thesis was a methodology for improving the accuracy of the 13C octanoic acid breath test, through direct measurement of carbon dioxide production rate (CO2). Investigation of gut sensitivity to specific fatty acids is an area which has been overlooked in previous literature. When adjustments were made for background intake of specific fatty acids, a 5-day high-fat supplemented diet was sufficient to accelerate gastric emptying rate and reduce satiety to a high-fat meal but had no effect on substrate utilisation. After a 5-day deadaptation period to high-fat feeding subjects still had reduced satiety, even though gastric emptying rate was similar to baseline levels. The findings of this PhD highlight the complexity of appetite regulation, over which control is based on a myriad of factors other than gastrointestinal transit. Furthermore, it was evident from this thesis that the process of adaptation to a high-fat diet may involve mechanisms other than desensitisation to a specific fatty acid. Dietary fat quality may have important implications in the obesity epidemic and associated disease.