Figure 1.

Mechanism of lactose intolerance. Lactose intolerance (right) occurs due to insufficient small intestinal lactase activity and/or a large quantity of ingested lactose. Its clinical manifestations are due to the undigested lactose being fermented by intestinal microbes leading to the release of high amounts of gases and lactic acids as well as drawing water into the intestinal lumen, causing abdominal pain, flatulence and diarrhea or watery stools. In a sufficient amount of lactase (left), lactose will be hydrolyzed into glucose and galactose and absorbed in the intestinal mucosa.