In the case of lactose intolerance, lactose utilisation is impaired due to lack of or decreased production of the digestive enzyme lactase.
Lactose is the carbohydrate in milk and is also called milk sugar. Lactose is split by the digestive enzyme lactose into glucose and galactose. This process makes lactose digestible for humans.
A total of around 90 per cent of the world's population suffers from a lack of lactase. However, most Europeans can eat milk and milk products all their lives without any problems. On the other hand, between 10 and 20 per cent of the European population suffer from lactose intolerance. For them, even small amounts of this component in milk triggers indigestion, so they have to resort to lactose-free foods.
In the majority of cases, lactose intolerance is genetic or arises in association with another disease of the digestive system (e.g. coeliac disease).