Exploring the role of short-chain fatty acids and resistant starch on energy balance, appetite control and glycaemic regulation

Background Obesity, a major public health issue, places individuals at increased risk of metabolic diseases, like type 2 diabetes (T2D). Increased intake of dietary fibre and non-digestible carbohydrates (NDCs) have been associated with improved energy balance and metabolic outcomes, such as fasting glucose, potentially mitigating chronic disease development. This thesis is formed of two parts: Part 1 Short-chain fatty acids (SCFAs) are produced via bacterial fermentation of fibre in the colon. Evidence suggests that SCFAs may play a role in obesity and chronic disease prevention (Chapter 1). To address a gap in the literature, a systematic review and meta-analysis investigating the effects of SCFA on glycaemia in humans was conducted in Chapter 2. Chapter 3 describes a clinical trial investigating the effects of inulin-propionate ester (IPE), a vehicle for colonic SCFA delivery, on weight gain prevention in younger adults at risk of weight gain. Chapter 4 outlines the mechanistic sub-study of this trial, investigating the effects of IPE on appetite hormones, energy intake, and energy expenditure. Chapter 5 discusses the findings of Part 1. Part 2 Resistant starch (RS), a type of NDC that remains largely undigested in the upper gastrointestinal tract, has been associated with improved glycaemic response. Chapter 6 outlines how increasing RS intake may modulate glycaemic responses. Chapter 7 presents a systematic review and meta-analysis of the effects of RS types on glycaemia in individuals with T2D and pre-diabetes. Chapter 8 investigates the effects of high-RS meals on glucose control in individuals with T2D. Chapter 9 discusses the work presented in Part 2. Summary This thesis highlights the need for further research into the effects of NDCs and SCFAs in energy homeostasis and metabolic response. It also emphasises the importance of fibre intake for preventing weight gain and the management of chronic diseases, like T2D.