4 FUNCTIONAL COMPONENTS AND MECHANISMS OF ACTION OF 'DIETARY FIBRE' IN THE UPPER GASTROINTESTINAL TRACT: IMPLICATIONS FOR HEALTH

摘要

1 INTRODUCTION Dietary fibre (DF) is a generic term for a chemically diverse group of carbohydrates that are resistant to endogenous enzymes of the human digestive tract, and includes various non-starch polysaccharides (both natural and synthetic), starches and short-chain oligosaccharides. This short review will focus on the structure and properties of naturally-occurring non-starch polysaccharides (NSP), specifically in the form of native cell wall polymer networks and also cell wall fractions of variable composition. The pioneering epidemiological studies of researchers, such as Trowell and Burkitt, helped to stimulate early research on DF, showing that fibre had much broader potential health benefits, notably for heart disease, diabetes, and cancer, than previously thought.1 Recent reviews have examined the physiological effects and health benefits associated with consumption of DF in more detail.~(2-5) For instance, NSP are now known to reduce the rate and extent of digestion and absorption of macronutrients, such as starch and lipid,~(6-8) which leads to attenuation of postprandial glycaemia, lipaemia and also fasting blood cholesterol.~(9-11) Such metabolic effects are linked to a reduced risk of developing coronary heart disease, stroke, obesity and type 2 diabetes mellitus. The mechanisms by which NSP are thought to alter the digestion kinetics and other gut functions are diverse, including formation of viscous solutions, encapsulation of nutrients, inhibition of digestive enzymes, and binding of bile salts. Furthermore, fermentation of NSP by microorganisms in the large intestine results in the production of short chain fatty acids (SCFA), which are now considered to have important positive effects on gut function and metabolism.~(12-13) This review will focus only on the mechanisms of NSP that are considered to alter the time course of digestion and postprandial metabolism.