Lactose Intolerance Information and Symptoms

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Lactose Intolerance Information and Symptoms. Jack Andersen / Getty Images

Lactose intolerance is a dietary intolerance caused and characterized by the inability to digest lactose sugar, one of the major components in milk. It is caused by a deficiency in a particular enzyme, lactase, that the body uses to digest that sugar. Treatment for lactose intolerance consists of either supplementing the body's supply of lactase enzyme or avoiding lactose-containing foods.

Causes of Lactose Intolerance

Lactose intolerance may occur for three reasons.

The first, and most common, is that the lactase enzyme present in the body from birth decreases over time as people get older, a condition known as "lactase non-persistence." The second is lactose intolerance caused by another digestive disorder, like Crohn's disease or celiac disease, or resulting from a gastrointestinal illness (which can damage lactase-producing cells). This type may be temporary. The third is hereditary and appears from birth. It can result in infants' being unable to digest breast milk and needing lactose-free formula.

Symptoms of Lactose Intolerance

Symptoms of lactose intolerance are primarily gastrointestinal and may include cramping, gas, bloating, nausea, or diarrhea. Most of the time, these symptoms occur between half an hour to a few hours soon after eating dairy products.

Diagnosis of Lactose Intolerance

Lactose intolerance can be diagnosed by a fasting blood test, by a breath test that measures byproducts of lactose digestion, or by a test that measures undigested lactose in stool.

The stool test is the test of choice in infants suspected of having lactose intolerance. Elimination diets may also be useful in addition to the above tests for diagnosing lactose intolerance.

Treatment of Lactose Intolerance

The simplest treatment of lactose intolerance consists of avoiding dairy products.

An over-the-counter lactase enzyme supplement is also available that can be taken before eating dairy products per package directions. Some high-lactose dairy products, like milk and ice cream, are available in lactose-free forms (this means they have already had lactase added so that their lactose sugar has been broken down). There is some evidence that probiotics -- helpful bacteria that naturally live in the digestive tract -- may help alleviate symptoms in some people with lactose intolerance.

Foods Containing Lactose

Many dairy products contain high levels of lactose. These include milk, fresh cream, butter, ice cream, cream cheese, and cottage cheese. Fermented dairy products, however, are formed by allowing bacteria to convert some or all of the lactose in milk into lactic acid. As a result, these dairy products are lower in lactose than fresh milk. Fermented dairy products include yogurt, kefir, sour cream, buttermilk, and crème fraîche. Hard cheeses, too, are made only from milk protein and include little or no lactose sugar.

Living with Lactose Intolerance

People with lactose intolerance vary in the amount of lactose they can digest without symptoms. Some can eat small amounts of lactose-containing foods, while others need to avoid dairy products more strictly.

Do be aware that dairy products can be found in unexpected products, such as canned tuna, salad dressings, chocolate, and artificial butter flavorings and margarine.

Secondary lactose intolerance -- lactose intolerance that is caused by another condition -- often eases when the other condition is cured. Avoiding dairy products for a short time after a gastrointestinal illness may be prudent.

Over-the-counter lactase supplements and lactose-free milks which are widely available, are effective at controlling lactose intolerance symptoms. Probiotics -- supplements of helpful bacteria -- are a possibly useful means of controlling lactose intolerance symptoms as well.

If your doctor believes that probiotics may be useful, you can either take probiotics in the form of yogurt (if your body tolerates yogurt ), or as capsules, usually found in refrigerated sections of health food stores.

If you do need to avoid dairy products entirely, be sure to replace the nutrients found in milk. All of the major nutrients found in milk are widely available in common foods.


He, T. "Effects of Yogurt and Bifidobacteria Supplementation on the Colonic Microbiota in Lactose-Intolerant Subjects." Journal of Applied Microbiology. EPub: Oct 10 2007.

McGee, Harold. "Milk Biology and Chemistry." On Food and Cooking. New York: Scribner, 1984. 16-32.

National Digestive Diseases Information Clearinghouse, "Lactose Intolerance Fact Sheet." 29 October 2007.

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