How come some people are lactose intolerant?

milk photo

From George Nelson

People with a lactose intolerance cannot digest lactose, a type of sugar mainly found in milk and other dairy products. This is usually because their digestive system does not produce enough lactase, an enzyme that breaks down lactose into other types of sugar in the small intestine so that it can be absorbed into the bloodstream.

Answered by Joanna Stass for Brain Dump, How It Works issue 110

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