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Thirty minutes has passed since you ate a bowl of ice cream, and now your stomach is cramping and you feel like you might have diarrhea. Does this sound like you? What if you substitute ice cream for milk, mashed potatoes, or even certain candies, and increase the time range to up to 2 hours later. Now does it sound like you? If either is true, you could have lactose intolerance.

Lactose is the main sugar in milk and most other dairy products. Your small intestine makes the enzyme lactase to help you digest that sugar. When you're lactose intolerant, you don't make enough lactase for good digestion. You can't cure lactose intolerance but you can make changes in what and how you eat to reduce its symptoms.

Check Your Symptoms

Millions of Americans have the uncomfortable and often embarrassing symptoms of lactose intolerance. 

  • Bloating
  • Cramps
  • Diarrhea
  • Painful gas
  • Nausea

Use trial and error to understand what foods cause symptoms, and in what amount, or you may want to see your doctor for an official diagnosis. You may be sensitive to small amounts of lactose-containing foods, or you may be able to eat a larger amount before you have symptoms. Your symptoms may be severe or mild. Everyone with lactose intolerance is different.

Identify the Culprits (Hint: It may not just be dairy.)

Milk and dairy products are the most popularly recognized as having lactose. To help prevent symptoms from lactose intolerance, read food product labels carefully. When shopping or cooking, look for these lactose-containing ingredients: 

  • Curds
  • Dry milk solids
  • Lactose
  • Milk
  • Milk byproducts
  • Nonfat dry milk powder
  • Whey

If you are extremely sensitive to lactose, you may need to avoid products such as: 

  • Baked goods
  • Bread, baking, and pancake mixes
  • Breakfast cereals
  • Certain types of candy, such as milk chocolate
  • Instant foods (breakfast drink mixes, mashed potatoes, soups, and meal replacement drinks)
  • Margarine
  • Nondairy creamers (liquid and powdered)
  • Nondairy whipped topping
  • Processed meats (bacon, hot dogs, sausage, and lunch meats)
  • Protein and meal replacement bars
  • Salad dressing

Getting a Diagnosis

Your doctor may ask you to keep a diary of the foods you eat, to note when you experience symptoms, and to stop eating an offending food to see if your symptoms disappear. To make a diagnosis, some doctors simply evaluate your symptoms and whether avoiding dairy products for two weeks relieves your symptoms.

To confirm the diagnosis, your doctor needs to do other tests.

  • Milk Challenge Test: This is typically the first test doctors recommend. You fast overnight and drink a glass of milk in the morning. Then you don't eat anything else for 3 to 5 hours. If you're lactose intolerant, you'll have symptoms within 2 hours. If the milk challenge test indicates you may have lactose intolerance, your doctor may do one of the following tests to confirm the diagnosis.
  • Hydrogen Breath Test: Normally you have very little hydrogen in your breath. If your body does not digest lactose, though, the levels of hydrogen build in your intestines and eventually hydrogen is in your breath. The test measures the amount of hydrogen in your breath after you drink a lactose-loaded beverage several times during a few hours. If your levels are high 3 to 5 hours later, your body is not digesting lactose properly.
  • Lactose Tolerance Test: This blood test measures the amount of glucose in your blood. When your body breaks down lactose, it releases glucose into your blood. After you have fasted, a small sample of your blood is taken. Then, you drink a liquid that is high in lactose. Two hours later, you give another blood sample. Because lactose causes blood glucose levels to rise, glucose levels in the second sample should be higher. If they aren't, your body hasn't digested the lactose.
  • Stool Acidity Test: Doctors use this test to check an infant or child for lactose intolerance. (It's very rare in infants.) First, your child drinks a liquid with high levels of lactose in it. Then, your child's doctor takes a small stool sample. The doctor checks the acidity level. If it’s acidic, your child may have lactose intolerance.
  • Intestinal Biopsy: The most direct test for lactose intolerance is a biopsy of the intestinal lining to measure lactase levels. However, since this is an invasive procedure, doctors don't usually measure lactase like this except for research purposes where the required specialized analysis is available.