Carbohydrate digestion

All carbohydrates absorbed in the small intestine must be hydrolyzed to monosaccharides prior to absorption. Hydrolysis precedes transport of monosaccharides in hamster intestine. From sucrose, glucose is taken up much faster than fructose. Monosaccharide transport saturates with D-glucose at 30 mM.

Digestion of starch begins with the action of salivary alpha-amylase/ptyalin, although its activity is slight in comparison with that of pancreatic amylase in the small intestine. Amylase hydrolyzes starch to alpha-dextrin, which are then digested by gluco-amylase (alpha-dextrinases) 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 (maltase, isomaltase, sucrase and lactase) present in the brush border of the small intestine. In the typical Western 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.

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