ABSTRACT
The physiological activity of carbohydrates in the gastrointestinal tract (GIT) is determined by their physical and chemical properties and the extent and location of their digestion within the GIT. Carbohydrates include those digested by mammalian digestive enzymes, such as alpha-amylase and the disaccharidases, as well as the carbohydrates that are digested by enzymes of microbial origin. The primary carbohydrates found in the diet that are digested by mammalian enzymes are starch, sucrose, fructose, lactose, and maltose. These carbohydrates, referred to as digestible carbohydrates, are sources of energy; however, they can also influence GIT responses to diet and result in adaptive changes in the GIT. The carbohydrates that are digested by microbial enzymes include the polysaccharides associated with dietary fiber (cellulose, hemicelluloses, pectin, and gums) as well as oligosaccharides such as inulin. Because these compounds are not degraded until the large intestine, their physical and chemical properties have important physiologic effects throughout the GIT. The properties associated with nonstarch polysaccharides (NSPs) and oligosaccharides include their water-holding capacity, viscosity, bile acid binding, and bulk or nondigestibility. In addition, these compounds are the primary substrates for growth of the microflora in the large intestine. Many compounds in the NSP fraction are an integral part of the cell wall in plants, and hence a significant component of
food structure. The Institute of Medicine (IOM) report on dietary fiber indicated that in addition to the effects of individual compounds in NSPs, this intact structure in foods is physiologically important.
