Abstract
It has been suggested that coffee drinking may confer a beneficial effect on health by reducing the risk of developing Type 2 Diabetes Mellitus (T2DM) and indeed there is much epidemiological evidence for a reduced incidence of T2DM in habitual coffee drinkers. However, many acute studies have reported a temporary worsening in postprandial glycaemia following caffeinated coffee (CC) consumption. Varied methodologies have been employed by these studies with many giving their participants large doses of coffee. In the acute studies conducted for this thesis, a single serving of CC increased the postprandial glycaemic response more than control (p=0.008), with no apparent dose-response effect. Furthermore, a single serving of decaffeinated coffee (DC) consumed in the morning, produced no effect on postprandial glycaemia, although a trend was observed for a reduction in the postprandial glucose peak (p=0.060) when DC was consumed at lunchtime. The majority of longer-term investigations have recruited habitual coffee drinkers who are likely to have already obtained any potential benefits of coffee consumption. The longer-term intervention reported in this thesis found no overall effects of twelve weeks of CC drinking on glucose and lipid metabolism in coffee-naïve individuals. However, differences were observed between fast and slow caffeine metabolisers when the analysis was split by phenotype. The fast caffeine metabolisers displayed a lower postprandial glucose response (p=0.019) and greater NEFA suppression (p=0.001) at baseline. Furthermore, significant interaction effects were observed between visit and phenotype for postprandial glucose (p=0.048) and NEFA (p=0.019), with the intervention producing an apparent increase in postprandial glycaemia in fast metabolisers and reduced NEFA suppression in slow metabolisers. In conclusion, no evidence was found for a beneficial effect of coffee drinking on glucose and lipid metabolism in the general population, however, individual differences in response to longer-term coffee drinking were observed which warrant further investigation.