Evidence suggests that high fibre diets can lower postprandial glycaemia. This effect is thought to come from a decrease in the rate of absorption of the digestible component of the carbohydrate, which flattens the blood glucose curve and decreases the area under the curve. Researchers have investigated the influence of gastric emptying on this phenomenon by feeding muesli containing 4g oat β-glucan fibre to 12 healthy subjects in a randomised cross-over trial. Following an overnight (8 hour) fast, the subjects consumed the muesli or a cornflake control and blood sugar was measured postprandially. Although the glycaemic response of the muesli meal was reduced when compared to the cornflakes, ultrasonography revealed that gastric emptying was not different between the two meals. There was also no significant effects of the muesli meal on satiety when compared to the cornflake control.
Figure 1. The structure of β-glucan fibre, containing mixed β-1, 3 and β-1, 4 glucosidic bonds.
These results suggest that fibre does not cause a reduction in postprandial glycaemia through a delay in gastric emptying. This likely explains its lack of effect on appetite control in the short-term. Evidence suggest that soluble fibre, such a β-glucan in oats, is able to reduce postprandial glycaemic through creation of a gel barrier in the unstirred layer of the enterocytes. This physical barrier prevents the diffusion of glucose and other monosaccharides into the enterocytes and slows sugar absorption. Although the short-term effects of fibre on appetite regulation are controversial. Their effect on maintaining a flatter and longer glucose curve, as well as their ability to be converted to short chain fatty acids in the colon, suggests that long-term appetite regulation may be more important. This may explain the long term benefits of fibre on weight loss and weight control.