What is lactose intolerance?

Lactose, the primary sugar found in milk, is a disaccharide composed of glucose and galactose.

Lactose is hydrolyzed to the monosaccharides glucose and galactose in the small intestine by the enzyme lactase.

The end products glucose and galactose are absorbed into the blood stream by active transport: galactose is covered to glucose and glucose is transported into cells.

If lactose is left undigested, it can cause symptoms such as nausea, cramping, bloating, abdominal pain, gas and diarrhea.

With age, many children lose their ability to digest large amounts of lactose, leading to lactose intolerance. Lactose intolerance, also known as hypolactasia or lactase deficiency, indicates low lactase activity in the brush border membrane of the small intestine.

Some people may have more or more severe symptoms than other. Other people display symptom after drinking one glass of milk, whereas others can tolerate up to a quart before suffering from abdominal cramps or diarrhea.
What is lactose intolerance?