Lactose intolerance is a digestive disorder caused by the inability to digest lactose, the main carbohydrate in dairy products. It can cause various symptoms, including bloating, diarrhea and abdominal cramps. People with lactose intolerance don’t make enough of the enzyme lactase, which is needed to digest lactose. Lactose is a disaccharide, meaning that it consists of two sugars. It is made up of one molecule each of the simple sugars glucose and galactose.

The lactase enzyme is needed to break lactose down into glucose and galactose, which can then be absorbed into the bloodstream and used for energy. Without sufficient lactase, lactose moves through your gut undigested and causes digestive symptoms.

Lactose is also found in breast milk, and almost everyone is born with the ability to digest it. It is very rare to see lactose intolerance in children under the age of five. Currently, about 75% of the world’s population is lactose intolerant. The risk varies greatly between countries.