Dietary fibre is composed of the non-digestible part of plant and can be classified as soluble or non-soluble. Within these broad categories of fibre are a number of sub groupings including cellulose, pectin, lignin, oligosaccharides, resistant starches, hydrocolloids and alcohol sugars. Different plant foods are complex mixtures of different types of dietary fibre. Fibre within the diet generally has the result of increasing digestion time because it provides bulk to the food bolus. Soluble fibre, present in fruits and legumes, is know to be particularly effective at increasing the transit time of food in the gut. This is of interest to nutritional scientists because decreasing the speed of carbohydrate absorption is known to allow better control of blood sugar levels and reduce post-prandial insulin and blood glucose concentrations. Fibre is also a rich source of vitamins and minerals, particular magnesium.
Research published in the Journal of Nutrition in 20101 used data collected from 75, 512 Caucasian, Japanese American and Native Hawaiian subjects aged from 45 to 75 years to assess the effects of diet on the risk of developing diabetes. The results showed that total fibre intake was associated with a reduced diabetes risk amongst both men and women. In men and women, the highest intakes of grain fibre were associated with a 20 % reduction in diabetes. The highest intakes of fibre from vegetables was associated with a 22 % reduction in risk of developing diabetes, but only in men. However, the fibre from fruit and vegetables was not associated with diabetes risk. High magnesium intakes also were protective of diabetes, and the authors concluded that because fibre is associated with magnesium in plants, the beneficial anti-diabetic effects of fibre might be because of its magnesium content.