What Is a Lactose Intolerance?

An Intolerance Doesn't Mean You Have to Avoid Dairy Completely

Milk pour in a glass
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When you drink milk, do you get gas, bloating, diarrhea, or other stomach abnormalities? These are some of the signs of a lactose intolerance, meaning your body may not be properly digesting the sugar found in some dairy products. It is rather common and there are ways that you can cut down the lactose in your diet without totally cutting out the dairy.


Lactose intolerance is a dietary intolerance caused and characterized by the inability to digest lactose sugar. This is 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. It's important to note that lactose intolerance is not the same as a milk allergy, which is common in children.

Lactose intolerance may occur for one of three reasons:

  • The most common is that the lactase enzyme present in your body from birth decreases over time as you get older. This is a condition known as "lactase non-persistence."
  • It may also be caused by another digestive disorder. These include Crohn's disease and celiac disease, though it may be the result of a gastrointestinal illness which can damage lactase-producing cells. This type of intolerance may be temporary.
  • The third cause is hereditary and appears from birth. It can result in infants being unable to digest breast milk and requiring lactose-free formula.


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 after eating dairy products.


A surprising number of people self-diagnose their lactose intolerance. In some of these cases, they may not actually have the deficiency. If you're concerned, it is best to speak with your doctor to get a formal diagnosis and advice that is tailored specifically to your health and medical needs.

Lactose intolerance can be diagnosed by a variety of tests. These include a fasting blood test, a breath test that measures byproducts of lactose digestion, or a test that measures undigested lactose in stool. The stool test is often used for infants.

Elimination diets may also be useful in addition to these tests for diagnosing lactose intolerance.


The simplest treatment of lactose intolerance is to avoid dairy products. An over-the-counter lactase enzyme supplement is also available that can be taken before eating dairy products. Be sure to follow the package directions when taking these.

Some high-lactose dairy products like milk and ice cream are available in lactose-free forms. This means they have already had lactase added in order to break down the lactose sugar so your body doesn't have to.

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.

Dietary Changes

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 are also made only from milk protein and include little or no lactose sugar.


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. These include canned tuna, salad dressings, chocolate, and artificial butter flavorings and margarine.

Secondary lactose intolerance — lactose intolerance that is caused by another condition — often eases as the other condition does. Avoiding dairy products for a short time after a gastrointestinal illness may be a good idea.

Over-the-counter lactase supplements and lactose-free milk can be 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 them in the form of yogurt (if your body tolerates yogurt) or as capsules (typically 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 other common foods.

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