Definition: Lactose is a type of sugar that is naturally present in milk. Many people suffer from lactose intolerance, meaning they are unable to digest significant amounts of lactose. As a result, they may develop symptoms that can include nausea, cramps, bloating, gas and diarrhea.
Lactose intolerance is caused by the lack of an enzyme called lactase, which is normally produced in the small intestine, where the enzyme breaks lactose down into a form that can be absorbed into the blood. In untreated celiac disease, the lining of the small intestine becomes damaged and production of lactase is impaired. Therefore, lactose intolerance is often associated with celiac disease. (For more information, see Lactose Intolerance and Celiac Disease.)
Lactose is hidden in many food products and medications. If you have lactose intolerance, in addition to watching out for "milk" in the ingredients list you should avoid whey, curds, milk by-products, dry milk solids, and nonfat dry milk powder.
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