At your best friend's sleepover party last weekend, everyone pigged out on cheese pizza and ice cream. Then they flopped on their sleeping bags for a night of DVDs. You were having a great time, but after about an hour you started feeling awful.

First your stomach felt really full — almost too full. Then it started to ache and you had a lot of gas — phew! Before long, you were running to the bathroom because you had to poop and you couldn't wait! Oh, no!

You hadn't been feeling sick before, and no one else felt yucky. So why was your stomach in knots? Maybe you have lactose intolerance (say: lak-tose in-tahl-er-ents).

What Is Lactose Intolerance?

People who have lactose intolerance have trouble digesting (say: dye-jest-ing) lactose, a type of sugar found in milk and other dairy foods. Lactose intolerance does not mean you are allergic to milk, but you will probably feel bad after drinking milk or eating cheese, ice cream, or anything else containing lactose.

As with everything else you eat, your body needs to digest lactose to be able to use it for fuel. The small intestine normally makes a special substance called lactase (say: lak-tase), an enzyme that breaks lactose down into simpler sugars called glucose (say: gloo-kose) and galactose (say: guh-lak-tose). These sugars are easy for your body to absorb and turn into energy.

People with lactose intolerance do not make enough lactase in their small intestine. Without lactase, the body can't properly digest food that has lactose in it. This means that if you eat dairy foods, the lactose from these foods will pass into your intestine, which can lead to gas, cramps, a bloated feeling, and diarrhea (say: dye-uh-ree-uh), which is loose, watery poop.

A lot of people have lactose intolerance, but no one has to put up with feeling awful. If you have lactose intolerance, you can learn to watch what you eat and your doctor may suggest medicine that can help.

Who Gets It and Why?

Between 30 million and 50 million people in the United States have lactose intolerance. That means at least 1 out of every 10 Americans is lactose intolerant.

Many cases of lactose intolerance are genetic (say: juh-neh-tik). That means that something in these people's genes makes them more likely to develop it. The condition is more common among some groups of people — about 90% or more of Asian Americans and Native Americans are lactose intolerant, and up to 80% of African Americans and Hispanic Americans get symptoms whenever they eat dairy foods. If you belong to one of these groups, you're also more likely to develop lactose intolerance while you're young.

People can also develop lactose intolerance for other reasons. Sometimes another illness may keep the intestine from producing enough lactase. For example, people with inflammatory bowel disease (IBD), such as Crohn's disease, or other long-term problems that affect the intestines are often lactose intolerant. People can also develop lactose intolerance if they're taking certain medicines or just had an infection that caused diarrhea. Luckily, this type of lactose intolerance doesn't usually last long.

Even if you don't have trouble with lactose now, there's a chance you might someday. Why? Because your body starts making less lactase when you're around 2 years old. The older you get, the more likely it is that you could have trouble digesting dairy foods.

Got Lactose Intolerance?

If you have lactose intolerance, your body will usually start acting up within 2 hours of eating or drinking something that has lactose in it. Not everyone reacts in the same way — or within the same amount of time — because some people can handle more lactose than others can. But when your body starts trying to digest the food, you'll begin to feel yucky.

If you once got a sick feeling in your stomach after gulping down a glass of milk, that doesn't mean you have lactose intolerance. But if you get an upset stomach every time you drink a milkshake, snack on ice cream, or eat a slice of cheesy pizza, there's a good chance that's what it is. Lactose intolerance can start suddenly — even if you've never had trouble with dairy products or other foods containing lactose.

What Will the Doctor Do?

If you and your parent think you might have lactose intolerance, the next step is to see your doctor. After hearing about your symptoms and doing a physical exam, your doctor may ask you to stop eating dairy for a period of time. If your symptoms improve on a dairy-free diet, but happen again when you try dairy again, there's a good chance you are lactose intolerant.

The doctor also can test your breath to see if you show signs of lactose intolerance. No, the doctor won't sniff to see if your breath smells stinky! He or she will check your breath for hydrogen (say: hye-druh-jun) — a gas you cannot see or taste. When lactose isn't digested, the bacteria that normally live in the large intestine use it and make hydrogen gas.

To test the amount of hydrogen, the doctor will have you drink something with lactose in it. You'll be asked to blow into a mask or bag to check the hydrogen level in your breath about every 15 minutes during the test. If it's high, you might have lactose intolerance.

If you're diagnosed with lactose intolerance, your doctor will talk to you about the best ways to treat it and help you feel your best. You will play a big part in how you feel because it's up to you to watch what you eat. You might want to keep a list of foods that make you feel sick, so you can steer clear of them in the future. Talking with a dietitian (say: dye-uh-tih-shun) — someone who specializes in food and nutrition — could help you decide what to eat and what not to eat.

The doctor also might suggest a kind of medicine you can take when you eat dairy products and other foods containing lactose. This medicine, which contains the lactase enzyme, comes in drops or pills and can be bought in drugstores and supermarkets. If you take it right before eating foods that cause you trouble, it usually helps your body digest the lactose.

Living With Lactose Intolerance

Some people with lactose intolerance must avoid all foods containing lactose, but others can eat certain dairy foods. Many people can drink lactose-free milk that has added calcium. Ask your doctor if this could be a good choice for you.

If you are new to lactose intolerance, start by figuring out what's best for you to eat. Again, a nutritionist can help you plan healthy meals that contain little or no lactose. When you do eat dairy products, stick with foods that have smaller amounts of lactose in them, such as aged cheeses, including cheddar.

Yogurt that contains live cultures is more easily digested because it contains healthy bacteria that produce lactase. Even if you're lactose intolerant, you may be able to handle smaller portions of your favorite dairy products. It also may help to eat a food that does not contain lactose along with a food that does, so have some fruit with your bagel and cream cheese!

If you have lactose intolerance, make sure you still get enough calcium from foods like tofu, leafy green veggies (spinach is a great choice), lactose-free milk, and juices or soy milk that have added calcium. Eating a healthy diet that includes many different kinds of food should do the trick.

If you can't seem to get enough calcium in your diet, your doctor may recommend a calcium supplement. You also need to get the right amount of vitamin D, which helps your body use calcium.

And if you're trying to cut out lactose, you'll have to cut out more than milk. Remember to check food labels because many packaged foods have added lactose, and sometimes it's tricky to figure out which ones do. Watch out for ingredients like butter, cheese, cream, dried milk, milk solids, powdered milk, and whey, for example. If you're not sure about an ingredient, ask an adult before you try the food.

So keep on enjoying your snacks and meals, but choose your foods and drinks wisely so you'll feel good before and after you eat!

Reviewed by: Mary L. Gavin, MD
Date reviewed: November 2008

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