lactose intolerance is the inability to digest the sugar in milk lactose. milk is an important source of nutrition for children and even some adults. with normal lactose tolerance all of the lactose is broken down (digested) in the intestine by an enzyme into two smaller sugars (galactose and glucose) which then are absorbed into the body. as a result normally no lactose reaches the colon. on the other hand in individuals with lactose intolerance who lack the intestinal enzyme that breaks down the lactose the ingested lactose is neither digested nor absorbed in the small intestine and reaches the colon where it is used by the bacteria in the colon. the bacteria produce chemicals that cause diarrhea and also produce gas. abdominal pain also may occur.
what is lactose intolerance?