Dietary fibre is a heterogenous group of non-digestible plant polysaccharides. Dietary fibre has traditionally been considered required to add roughage to food, and little more. However, more recently dietary fibre of various varieties has been shown to have wide ranging metabolic roles in lipid and glucose metabolism. The low fibre content of the typical Western diet is now considered a contributory factor in the development of Western lifestyle diseases, and this has largely been attributed to the detrimental glycaemic effects that occur in such low fibre diets. The ability of fibre, particularly soluble fibre to control blood glucose levels, suggests that dietary fibre may be conditionally essential. In this regard, the fibre content of the diet may need to reflect the starch content of the diet such that higher starch diets necessitate higher fibre diets. Of the fibres, the gums, found in high amounts in leguminous plants, may be particularly beneficial in this regard when considering supplemental fibre.
The postprandial glycaemic effects of gum fibres have been investigated in diabetics. In one study for example1, researchers tested the effects of guar gum supplements on the degree of glycosuria (glucose in the urine) in a group of subjects with diabetes. Subjects consumed 14 to 29 grams of guar gum fibre daily for 5 days. The carbohydrate content of the diets of the subjects ranged from between 22 and 61 % of total calories. In those diets where carbohydrate represented more than 40 % of the total dietary intake of calories, there was a mean reduction of glycosuria by 64 % over the last 2 days of the study. However, with carbohydrates below 40 % of total calories no significant effects were evident from guar gum supplements. Therefore these data suggest that fibre may be required for correct postprandial blood sugar control, when starch intake increases above a certain threshold. This in turn lends weight to the argument that fibre is conditionally essential in the human diet.
Supplemental fibres have shown some benefits to postprandial glycaemia. However, their effects are often inconsistent. In contrast fibre rich foods appear to show more consistent effects in the literature. The obvious solution to maintaining the correct starch to fibre ratio may therefore be to eat whole plant foods containing their original fibre. Nature in Her wisdom has added fibre to plant foods and this allows humans to moderate the rise in blood sugar caused by consumption of these foods. Refining the starch to remove the fibre, and let us not forget the vitamin and minerals, accentuates the rise in blood sugar seen in response to the starchy food. Such uncontrolled rises are now through to increase the risk of developing insulin resistance, which causes a raft of downstream metabolic changes that can be grouped under the umbrella heading of the metabolic syndrome. Such changes include blood lipid changes, inflammation, oxidative stress and endothelial dysfunction.
RdB
