- Lactose Intolerance is caused by a deficiency of lactase, an enzyme present on the small intestine epithelium's brush border, which digests the inabsorbable disaccharide 'Lactose' into the absorbable monosaccharides glucose and galactose (See: Carbohydrate Digestion and Absorption). Nearly all individuals express lactase as neonates in order to properly digest maternal milk; however, expression declines in many ethnicities with age. Lactose intolerance tends to be more frequent among African Americans.
- No morphological abnormalities of the mucosa are observed.
- Osmotic diarrhea following ingestion of milk or other dairy products.