The role of carbohydrate food structure in gastrointestinal digestion, glycaemic response, and appetite regulation

Abstract

Dietary fibre has demonstrated benefits against many metabolic diseases such as type 2 diabetes and obesity. Plant cell walls are the primary source of dietary fibre, and the structural integrity largely determines their physiological effects. Intact cell walls encapsulate starch to slow down its digestion and may protect the transport of resistant starch to the large intestine, thereby promoting short-chain fatty acid production and appetite control. However, cell wall structures can be disrupted when plant foods are processed into small particles, which may eliminate health benefits. This thesis aimed to understand the impact of the structural integrity of plant cell walls on human digestion, postprandial glycaemia and appetite using chickpeas as a food model.

Chapter 2 reviewed and meta-analysed 13 randomised crossover trials (RCTs) showing that the large particles of starchy food lowered postprandial glycaemia in healthy subjects. Chapter 3 designed a two-phase, double-blinded RCT that enabled the examination of digestion and postprandial response in humans. Chickpeas were processed into three structures: broken cells (Broken), intact single cells (Intact-S), and intact cell clusters (Intact-C). Chapter 4 studied their digestion in the stomach and duodenum and revealed that Intact-S and Intact-C remained their structures largely intact in the upper gastrointestinal tract, thereby lowering the luminal carbohydrate release and attenuating postprandial glycaemia. Chapter 5 further investigated the digestion behaviours in the terminal ileum and appetite outcomes. Both intact structures delivered more carbohydrate contents to the distal ileum than Broken. Intact-S was more digestible in the ileum whilst Intact-C retained more carbohydrate for ileal and colonic fermentation. Fermentation levels increased 4-8 hours postprandially, while Intact-C increased ileal acetate, PYY and fullness compared to Broken.

Intact-C presented the greatest benefits in attenuating postprandial glycaemia, promoting fermentation, and suppressing appetite. Our work emphasises the structural integrity of dietary fibre-rich foods in achieving their beneficial effects.