Lactose intolerance is the inability to digest dairy products containing lactose, most notably milk. Lactose is a sugar that is broken down in the body by an enzyme called lactase. Lactase is normally secreted by cells lining the small intestine, and breaks down lactose into glucose, which is then absorbed into the bloodstream. When lactase is deficient, undigested lactose begins to ferment in the lower intestines. This can cause physical discomfort ranging from bloating, nausea and gas to cramps and diarrhea.
While it is rare for children to be born without the ability to produce lactase, after about 2 years of age the body's production of this enzyme diminishes. It's not unusual then that so many adults are affected by lactose intolerance to varying degrees. The severity of the physical discomforts will depend on how much lactase a person produces in relation to how much lactose is consumed. For example, one glass of milk may not cause a person any problems, while two glasses could.
Lactose intolerance has a tendency to correlate to certain ethnic groups with a suggestion that populations that evolved consuming high amounts of milk, such as herders, have a higher tolerance for lactose than populations that were not involved in animal husbandry. In any case, this condition affects an estimated 30-50 million Americans, with 90% of Asian Americans affected and at least 75% of African American and American Indians.
There are common tests your doctor can perform to find out if you are lactose intolerant. A lactose-rich liquid is consumed after a short fast. The doctor might then draw several blood samples over a 2-hour period to see how the body is digesting the lactose. If digested properly, it should be converted to glucose that will be found the blood. Or, if you opt for the hydrogen breath test, your breath will be tested for the presence of hydrogen. Hydrogen is normally not present in the breath except in very small quantities, but fermenting lactose will produce greater amounts of hydrogen that will be detected and measured.
If a very young child or an infant needs to be tested for lactose intolerance, an alternate test is available that checks for acidity in the stool. Undigested lactose creates lactic acid and other fatty acids that will be found in the stool sample.
Lactose intolerance is controlled through diet. Often a small amount of lactose is fine and it is simply a matter of finding your level of tolerance and limiting foods with lactose content. Lactase enzymes are also available over the counter. Taken with lactose food, the enzymes break down the lactose for your body. Lactose-reduced dairy products are also an option.
People who don't eat lactose products may be concerned about calcium intake. Many non-dairy foods are high in calcium, such as green vegetables like broccoli and kale. Some types of fish are also high in calcium.