Lactose intolerance is very common among American Indians and those of Asian, African, Jewish and Hispanic descent. Northern Europeans, a few African tribes, some Mediterranean peoples and descendants of each of these are the only people who typically do not develop lactose intolerance. No one knows exactly why, but genetics no doubt plays a role. Incomplete digestion Lactose intolerance is caused by the incomplete digestion of lactose, the sugar contained in milk. At birth and in early childhood, your body produces large amounts of an enzyme called lactase.
Lactase breaks down lactose and allows it to be absorbed.
However, as you grow up, you usually produce less lactase. By the time you're a teen, you generally produce only about 10 percent of the lactase you did as an infant. With less lactase available to break down lactose, your body can no longer comfortably digest the amounts of milk and ice cream that it previously handled easily. If you take in more lactose than you're capable of digesting, the incomplete digestion can lead to gas, stomach cramps, bloating and diarrhea. Tests to help identify lactose intolerance As obvious as these symptoms may be, lactose intolerance is not easily diagnosed by its symptoms alone.