The influence of the physical state and habitual mastication on the glycaemic response and satiety

The escalating levels of obesity highlight the need to better understand the mechanisms underlying energy intake and energy regulation. The blood glucose response (GR) has been shown to significantly influence short term food intake and therefore energy balance. Regulating the GR is also important in diabetes and impaired glucose tolerance; conditions which are also closely linked with obesity. Poor glycaemic control has moreover been shown to increase risks of other chronic diseases such as cardiovascular disease (CVD). Factors affecting the GR will therefore impact both on energy regulation and chronic diseases. A large number of factors influence the GR. A complete understanding of all these variables is essential if successful regulation of the GR is to be achieved. The studies presented in this thesis focused on two factors affecting the GR that have hitherto received little research attention. These are the physical state (liquid-sold nature) of food and habitual mastication (ingested particle size). The first study investigated the effects of the physical state and showed that it affected the shape and amplitude of the GR and insulin response (IR) curves but not the total metabolic response. The response pattern implied that liquids were satiating for a shorter length of time compared to solids. The subsequent study then investigated the effect of carbohydrate-based energy containing beverages on satiety and short-term food intake and found that they were detected by the physiological energy regulatory systems and suitably compensated for. However, there was a notable gender-wise variation in compensation efficiency. Whilst consuming a carbohydrate beverage does not appear to affect short-term energy balance of males it could induce a positive energy balance in females. Using both in vitro and in vivo models, other studies forming this thesis showed that the degree of particle size breakdown during habitual mastication influenced the magnitude and pattern of the GR. Therefore, habitual mastication appears to be a significant contributor to between-individual variations in the GR. It was noted, however, that these effects were only observed with rice but not spaghetti. The thesis also showed that salivary - amylase could potentially be a significant contributor to the GR, at least in those who spend a longer time masticating. The final study in the thesis showed further that the particle size of ingested food correlated inversely with the GR, IR and rate of gastric emptying. Differences in between-individual variations in the GR, IR, gastric emptying and post-gastric digestive aspects when ingesting food with varying particle sizes are also discussed.