A physico-chemical perspective of plant polysaccharides in relation to glucose absorption, insulin secretion and the entero-insular axis.

Abstract

There is a growing realization that studies of the physico-chemical structure and properties of foods in the gut lumen will greatly assist our understanding of the function of the gastrointestinal (GI) tract in relation to human health and disease (British Nutrition Foundation, 1990). However, it is difficult to make reliable predictions of the behaviour of foods in the gut, because there are serious deficiencies in our knowledge and methodology in this area. Our knowledge of GI function at the luminal, mucosal and cellular levels is unlikely to make significant progress until we have a detailed and basic understanding of the structure and properties of foods. Thus, for example, the behaviour of a food matrix in the GI environment is of critical importance to our understanding of the kinetics of nutrient bioavailability. Interestingly, the mechanical properties of foods have been studied extensively in relation to their behaviour in the mouth, in order to understand, for example, the process of mastication and how human subjects perceive texture (Blanshard & Mitchell, 1988; Vincent, 1990). This approach has not been used in any fundamental way, however, to study the relationship between the physical properties of foods and their effects on GI function and systemic responses, such as meal-stimulated blood metabolite and hormone levels. Non-starch polysaccharides (NSP) from plant food sources are of special interest to nutritionists in that they have marked effects on the physical properties of digesta at all sites of the GI tract (Selvendran et al. 1987; Eastwood & Morris, 1992; Moms, 1992). Thus, the consumption of NSP (‘dietary fibre’) in the form of plant cell walls or purified extracts can strongly influence GI function, including the rate and extent of nutrient absorption in the small intestine and bacterial fermentation in the colon. The present paper is a brief review of the possible physico-chemical mechanisms by which NSP, mainly the water-soluble polymers, influence glucose absorption, insulin secretion and the entero-insular axis.