Implications of altering the rate of carbohydrate absorption from the gastrointestinal tract

The rate of absorption of carbohydrate from the small intestine plays a major role in determining the metabolic effects of dietary carbohydrate. Factors which reduce the rate of absorption include the nature of the starch and sugars, and the presence of vegetable proteins, fats, viscous fibre, and antinutrients, including lectins and phytates. The rate of absorption can also be manipulated by the use of specific enzyme inhibitors and by increasing the number and frequency of meals while holding caloric intake constant. All these factors contribute to the creation of what may be termed slow release or "lente carbohydrate". The slowing of small intestinal absorption, as exemplified by increased meal frequency ("nibbling"), results in reduced postprandial insulin secretion and lower low-density lipoprotein (LDL) cholesterol and apolipoprotein B concentrations. A further effect of some manipulations which reduce the rate of absorption is increased delivery of carbohydrate to the colon and its absorption after bacterial fermentation to short-chain fatty acids (SCFA). These SCFA may have beneficial effects on colonic health(butyrate) or further inhibit cholesterol synthesis in the liver (propionate). Thus the absorption of "lente carbohydrate" takes place along the full length of the gastrointestinal tract with a wide variety of physiological consequences.