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What Is Lactose Intolerance?

People who have lactose intolerance (say: LAK-tose in-TAHL-er-ents) have trouble digesting (say: dye-JES-ting) lactose, a type of sugar found in milk and other dairy foods. Lactose intolerance does not mean a kid is allergic to milk, but they will probably feel bad after drinking milk or eating cheese, ice cream, or anything else containing lactose.

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.

What Happens in Lactose Intolerance?

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.

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.

What Are the Signs of 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 an 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. Thery'll 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 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 do have 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 contains the lactase enzyme. It 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 some 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. 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.

You may also take a lactase enzyme supplement. Taking this before eating food that contains dairy will help your body digest the lactose sugar in dairy so you don't have pain, cramping, bloating, gas or diarrhea.

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!

Medically reviewed by: J. Fernando del Rosario, MD
Date reviewed: May 2023