Plants contain a variety of carbohydrates, some of which contain glycosidic bonds that are not able to be digested by humans. Such carbohydrates are classified as dietary fibre, and were once thought to be nutritionally significant only because they provided bulk to food. However, as knowledge of nutrition has advanced, these non-digestible carbohydrates have been shown to have important physiological roles in energy production, hormonal modulation, blood glucose regulation and weight control. Plant fibres are diverse but are generally divided into the groupings of soluble and insoluble fibres. Of these soluble fibres are thought to form a viscous gel in the gut, and this may increase nutrient transit times and also form a barrier along the lining of the small intestine. This may be beneficial because it may slow the rate of glucose absorption to the blood and thus limit the glycaemic effects of foods.
For example,, in one study1 researchers assessed the physiological effects of pectin fibre from apples. Subjects with type 2 diabetes ate a low fibre diet for 2 weeks and then had their diet supplemented with 20 g pectin per day. As has been shown in previous studies, pectin slowed digestion be decreasing the gastric emptying half-time by 43 %. Addition of fibre to the diet also decreased the area under the curve for glucose, indicative of a slower rate of glucose absorption from the gut. These results suggest that pectin is able to modulate glucose absorption from the gut, and this may be due to decreased gastric emptying. However, no correlation could be found between the gastric emptying rate and glucose area under the curve in this study. Interestingly, the decreased gastric emptying rate remained for up to 3 days after pectin supplementation had ceased, suggesting that dietary fibre may have a hormonal role beyond its bulking properties.