Digestion and metabolism of carbohydrates

Abstract

Carbohydrates are the single most abundant and economic sources of food energy in the human diet, constituting 40–80% of total energy intake in different populations. Carbohydrates are classified according to their degree of poly-merization into sugars, oligosaccharides, and polysaccharides – the last consisting of starches with different degrees of resistance to digestion – and dietary fibers or nonstarch polysaccharides. Glycemic carbohydrates are digested (hydrolyzed by enzymes) to sugars (monosaccharides) in the small bowel and absorbed and metabolized.Nonglycemic carbohydrates are fermented in varying degrees to short-chain fatty acids (SCFAs), carbon dioxide, hydrogen, and methane in the large bowel. Absorbed SCFAs are metabolized in colonic epithelial, hepatic, and muscle cells. For optimum function of the nervous system and other cells, blood glucose concentrations are tightly controlled by a group of hormones (insulin in the absorptive phase; glucagon, epine-phrine, and cortisol in the postabsorptive phase), utilizing several possible metabolic pathways for glucose anabolism and catabolism. Intakes of optimum amounts of different types of carbohydrates are associated with good health through effects on energy balance, digestive functions, blood glucose control, and other risk factors for several chronic diseases