Carbohydrate digestion begins with salivary alpha-amylase breaking starch down into alpha-dextrin in the mouth. Alpha-dextrin is further broken down by gluco-amylase into maltose and maltotriose. Enzymes such as maltase, isomaltase, sucrase and lactase then hydrolyze these sugars and other disaccharides into monosaccharides. Carbohydrate digestion is usually fast in the upper small intestine but can occur throughout the small intestine and even in the large intestine by bacterial flora if the carbohydrates are not easily digestible. Undigested carbohydrates in the small intestine and resistant starches are metabolized by

1. CARBOHYDRATE DIGESTION
Digestion of carbohydrates begins with the action of salivary alpha-amylase. Amylase hydrolyzes
starch to alpha-dextrin, which are then digested by gluco-amylase to maltose and maltotriose. The
products of digestion of alpha-amylase and alpha-dextrinase, along with dietary disaccharides are
hydrolyzed to their corresponding monosaccharides by enzymes such as maltase, isomaltase,
sucrase and lactase. In the typical diet, digestion and absorption of carbohydrates is fast and takes
place usually in the upper small intestine. However, when the diet contains carbohydrates not
easily digestible, digestion and absorption take place mainly in the ileal portion of the intestine.
Digestion of food continues while simplest elements are absorbed. The absorption of most digested
food occurs in the small intestine through the brush border of the epithelium covering the villi. It
occurs by active transport and requires energy by the epithelial cells.
Carbohydrates not digested in the small intestine, including resistant starch foods such as potato,
bean, oat, wheat flour etc are digested in a variable when they reach the large intestine. The
bacterial flora metabolize these compounds anaerobically in the absence of oxygen. This produces
gases such as hydrogen, carbon dioxide and methane and short-chain fatty acids such as acetate,
propionate, butyrate. Fatty acids are rapidly metabolized. Thus butyrate, used mainly in the
colonic, is an important nutritional source for these cells and regulates their growth.