Sugar comes in many forms. One type of sugar, lactose, occurs primarily in milk. Nature gives young children the ability to digest lactose, because they need to do so when they nurse. However, as people grow up, they often lose the lactose-digesting enzyme, known as lactase. The result is a condition called lactose intolerance. Symptoms include intestinal cramps, gas, and diarrhea following consumption of lactose-containing foods.

Lactose intolerance is most prevalent in people of Hispanic, African, Asian, Middle Eastern, or Native American descent, although Caucasians can develop it as well. Treatment consists primarily of avoiding foods containing lactose, such as milk and ice cream. Use of lactase supplements may help people who are lactose intolerant handle more lactose than otherwise. Also, special milk products are available from which the lactose has been removed (often through the use of lactase).