Impaired ability to digest lactose, maltose, or sucrose, due to lack of lactase, maltase, or sucrase in the small intestinal mucosa. The undigested sugars remain in the intestinal contents, and are fermented by bacteria in the large intestine, resulting in painful, explosive, watery diarrhoea. Treatment is by omitting the offending sugar from the diet.
Lack of all three enzymes is generally caused by intestinal infections, and the enzymes gradually recover after the infection has been cured. Lack of just one of the enzymes, and hence intolerance of just one of the disaccharides, is normally an inherited condition. Sucrose intolerance due to genetic lack of sucrase is common among the Inuit.
Lactose intolerance due to loss of lactase is normal in most ethnic groups after puberty; it is only among people of northern ethnic origin that lactase persists into adult life.
Subjects: Medicine and Health.