This is due to lack in the INTESTINE of the ENZYME known as LACTASE, which is responsible for the digestion of lactose, the sugar in milk. In people with lactose intolerance, drinking milk or eating milk-containing products causes nausea, a sensation of bloating or distension in the gut, abdominal pain and diarrhoea. (Similar disturbances after taking milk may also occur in those who have an allergy to milk protein.) Treatment is by means of a low-lactose diet, achieved by avoiding fresh or powdered milk and milk puddings. Many can tolerate fermented milk products, as well as the small amounts of milk used in baking and added to margarine and other food products. However, infants may have to be fed exclusively on a lactose-free formula, as even breast milk may produce symptoms.