Dietary fibre, lente carbohydrates and the insulin-resistant diseases

Several epidemiological studies link consumption of fibre-rich foods to a r educed risk of type 2 diabetes and CHD. The 'fibre hypothesis' suggested th at this was a direct effect of fibre. However, fibre-rich foods contain dif ferent types of fibre as well as other potentially beneficial compounds, an d many foods naturally high in fibre have low glycaemic and insulinaemic in dices, possibly due to food form. The question therefore emerges as to the effect of isolated fibre per se on insulin sensitivity, lipids and other ri sk factors associated with the metabolic syndrome. Many beneficial effects are seen with pharmacological doses of isolated viscous soluble fibre, incl uding improved insulin sensitivity, decreased LDL-cholesterol levels and de creased clotting factors. Similar effects are seen with low glycaemic-index foods. In contrast, insoluble non-viscous cereal fibre is not seen to act directly on risk factors when taken in refined foods such as in milled flou r. Since cereal fibre, the major type of fibre in western diets, does not d irectly act on the risk factors for the metabolic syndrome, the question re mains as to possible mechanisms. Until now, fibre and the nature and proces sing of the starch and particle size have been seen as the main determinant s of the metabolic response to starchy foods. However, fibre-rich foods als o have an increased protein-to-carbohydrate ratio. Hence we suggest that th e protective effect of fibre may also be due to increased vegetable protein content, which may act directly to reduce clotting factors and oxidized LD L-cholesterol levels.