Dietary fibre, diabetes and obesity

An increased intake of dietary fibre appears to be useful for the treatment of both obesity and diabetes mellitus. Fibre-rich food is usually satisfying without being calorically dense. Supplementing a normal diet with gel-forming fibres, such as guar gum, leads to an increased satiation probably due to a slower gastric emptying. Recent long-term studies have confirmed the usefulness of viscous fibres as an adjunct to regular dietary treatment of obesity. Apart from a beneficial effect during caloric restriction, dietary fibre may improve some of the metabolic aberrations seen in obesity. Gel-forming fibres are particularly effective in reducing elevated LDL-cholesterol without changing the HDL-fraction. Impaired glucose tolerance or manifest diabetes is also improved. These effects are probably in part associated with the gelling property of the fibre which leads to an increased viscosity of the unstirred layer thereby delaying the absorption process. Other sources of dietary fibre with a high content of viscous gums, such as oats, have been shown to reduce LDL-cholesterol. Increased intake of viscous fibre leads to a gradual reduction in fasting glucose levels in diabetics. The reason for this is unclear but it cannot readily be explained by a delayed absorption process. Since insulin levels are also reduced these findings suggest that insulin resistance is alleviated. Recent studies with the euglycemic clamp technique support this possibility. Glucose uptake by isolated fat cells and both insulin sensitivity and responsiveness are also increased.