Fiber, inulin and oligofructose: similarities and differences

The biological, chemical and physical properties of dietary fibers are associated with physiologic actions in the small and large intestine that have important metabolic implications for health. These properties of fiber include dispersibility in water, bulk, viscosity, adsorption and binding of compounds and fermentability. Dietary fructans share some of the properties of dietary fiber and thus are likely to have similar metabolic effects. Within the small intestine, properties such as dispersibility in water, bulking and viscosity are associated with slowing the digestion and absorption of carbohydrate and lipid and promoting nutrient absorption along a greater length of the small intestine. Both of these actions are related to cholesterol reduction and blunting of alimentary gylcemia. Although fructans are dispersible in water and will provide some bulk because they are nondigestible in the small intestine, they do not appear to be associated with significant increases in viscosity. Thus one would predict that any immediate effects on alimentary glycemia or on cholesterol reduction are likely to be modest compared with more viscous polysaccharides. Fermentability and bulking capacity of nondigestible carbohydrates define an essential role of fiber in maintaining gastrointestinal health. Within the large intestine, carbohydrates that are not digested in the small intestine are available for fermentation by the microflora present. Carbohydrates that are dispersible in the aqueous phase are more readily digested by microbes. A large body of evidence indicates that dietary fructans are digested in the large intestine, resulting in an increase in microbial mass and production of short-chain fatty acids.