These enzymes break down disaccharides to monosaccharides like glucose, galactose and fructose that are easily absorbed. Glucose is transported via an active process that exchanges sodium for glucose. Fructose is absorbed via passive diffusion. Monosaccharide absorption is rapid and efficient in all parts of the intestine but absorption is best in the duodenum. A genetic loss of intestinal disaccharidases causes malabsorption.
Lactose intolerance is probably the most well known malady caused by the lack of a disaccharidase.
Upon the ingestion of milk products, diarrhea results because the lactose remains in the intestinal lumen drawing water with it. Much of the world's adult population is lactose intolerant. No protein digestion occurs in the mouth. Hydrochloric acid and pepsin in the stomach begin protein digestion. In the duodenum, proteins are digested to amino acids that are rapidly absorbed into the enterocytes.