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What is Lactose Intolerance?

Lactose [LAK-tohs] intolerance [in-TOL-er-uhns] is a digestive condition in which the body can’t digest lactose. Lactose is the natural sugar found in milk and dairy products. In order for the body to absorb lactose from the intestines and into the body, it needs to make a chemical called lactase [LAK-tayz]. Lactase breaks lactose down into 2 smaller sugars that can be absorbed by the body.

People that don’t make enough lactase are lactose intolerant and can’t absorb the sugar. The lactose passes through the gut where certain bacteria are able to use it instead. These bacteria increase certain activities which cause the symptoms of lactose intolerance.


The symptoms of lactose intolerance include:

  • Gas
  • Diarrhea
  • Nausea
  • Stomach cramps
  • Bloating

When to See a Doctor

See your doctor if you have any of the symptoms of lactose intolerance after drinking milk or consuming dairy products.


People with lactose intolerance don’t have enough lactase, the chemical that helps break down lactose in the body. Lactase breaks lactose into 2 smaller sugars that the body can absorb into the bloodstream.

Lactose intolerance is usually passed down through families and is quite common among adult African Americans, Native Americans, and Asian Americans. Most people are born with lactase and the ability to digest lactose. However, if lactose intolerance runs in their families, they often have less lactase as they get older.

Diagnosis and Tests

There are three different tests used for diagnosing lactose intolerance:

  • Lactose tolerance test. During this test, your doctor can measure your blood sugar levels after drinking a high-lactose drink. If your blood sugar level doesn’t rise, it may mean that your body isn’t digesting lactose.
  • Hydrogen [HAHY-druh-juhn] breath test. This is similar to the lactose tolerance test, except after drinking a high-lactose drink, you will breathe into a device instead of having blood tested. The device will measure the amount of hydrogen gas in your breath. Normally, very little hydrogen is found in the air you breathe out. However, if your body can’t digest lactose, hydrogen levels rise in your breath.
  • Stool test. If a patient is unable to do either a blood or breath test, they may be able to submit a stool (poop) sample for a stool acid test. This is often the test used in infants and very young children. After drinking a high-lactose drink, their stool is tested. If the stool becomes more acidic, it means the patient is unable to digest lactose.


There is no treatment to help the body make lactase, but symptoms can be prevented or controlled through your diet. Also, dietary supplements containing lactase are available to help digest foods with lactose.


While there’s no know way to prevent developing lactose intolerance, the symptoms of lactose intolerance can be prevented by:

  • Taking dietary supplements containing lactase
  • Making changes to your diet

Diet changes will depend on the severity of the condition. You may need to eat less of, or remove from your diet, these foods:

  • Milks
  • Creams
  • Ice cream and sherbet
  • Yogurt
  • Some cheeses
  • Butter

Sometimes, lactose is added to some boxed, canned, or frozen foods, including:

  • Breads
  • Baked goods
  • Mixes for baked goods
  • Cereals
  • Instant foods
  • Lunch meats
  • Candies
  • Salad dressings
  • Frozen meals
  • Margarine

Support and Resources

American Academy of Allergy Asthma & Immunology: Lactose Intolerance

MedlinePlus: Lactose Intolerance

U.S. Food & Drug Administration: Problems Digesting Dairy Products?
Lactose intolerance is a condition in which the body can’t digest lactose. Lactose is the natural sugar found in milk and dairy products. In order for the body to digest lactose, it needs to make a chemical called lactase. Lactase breaks lactose down into simple sugars that the body can absorb.
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