Lactose Intolerance

Lactose, also known as milk sugar, is the major carbohydrate found in milk. Its sweetness is 16% that of sucrose (table sugar). The lactose content of mother's milk obtained by nursing infants [7-8% (m/m)] is almost twice that in cow's milk [4-5% (m/m)]. Lactose supplies about 40% of the energy in human milk.

Many adults lack the enzyme lactase, necessary for the digestion of lactose; this causes lactose intolerance. When lactose molecules remain in the intestine undigestded, they attract water to themselves, causing fullness, discomport, cramping, nausea, and diarrhea. The level of lactase in humans varies with age. Most people have sufficient lactase during childhood years when milk is a needed calcium source. In adulthood, lactase levels decrease and lactose intolerance develops. This explains changes in milk-drinking habits of many adults. About one-third of Americans suffer from lactose intolerance.

The level of the enzyme lactase in humans varies widely among ethnic groups, indicating tht the trait is genetically determined (inherited). The occurence of lactose intolerance is lowest among Scandinavians and other nothern Europeans and highest among native Americans, Southeast Asians, Africans, and Greeks.

[Source: Chemical Principles by H. Stephen Stoker]