Lactose Intolerance

What is Lactose Intolerance?

What is it?
This is sensitivity to foods that contain lactose. Lactose is a sugar most often found in dairy products. It is a common problem and can affect anyone, but is most common among Native American, Asian, and black people. This is not a food allergy, just the sugar present is dairy products, lactose, cannot be absorbed.

Why does it happen?
This disorder is linked to low levels of or not properly working, lactase. Lactase is the chemical present in the body that is responsible for breaking down lactose. This decreased amount of lactase can be due to injury of the lining of the GI tract or because of genetics. If lactose is not broken down, it cannot be absorbed in the small intestine. The lactose then travels to the colon and the bacteria present there break it down.

What are the symptoms?
Symptoms are triggered after eating milk or dairy products and can include:

  • Diarrhea
  • Abdominal pain
  • Flatulence
  • Bloating
  • Vomiting

How is it diagnosed?

  • Lactose tolerance testing. In this test, a specific amount of lactose is eaten and blood is taken to look at the sugar levels. Blood is drawn right away, in 60 minutes and then at 120 minutes after eating the lactose. A positive test is if the blood sugar level is not increased by a certain level and symptoms develop. This test can be falsely negative if you have diabetes or bacterial overgrowth.
  • Lactose breath hydrogen test. This test is more frequently performed. Again, a specific amount of lactose is eaten and the amount of hydrogen in your breath is measured every 30 minutes for 3 hours. Recall, if lactose reaches the colon it is broken down by bacteria. This breakdown releases hydrogen. The amount of hydrogen you breathe out is measured. Typically, lactose is fully absorbed prior to reaching the colon so if you have normal levels of functional lactase there is not an increased level of hydrogen. Lung disorders, smoking, and recent use of antibiotics can impact the results.
  • Upper endoscopy with small intestinal biopsy.
  • Genetic testing. This is rarely performed.

How is it treated?
The goal of treatment is to eliminate symptoms. This is typically accomplished by:

Decreasing the amount of lactose that is eaten.

  • This means avoiding dairy products like milk, cream, yogurt, cheese, and
  • butter.
  • Read labels on food products as lactose may be a hidden ingredient; look for “milk byproducts”, dry milk powder, dry milk solids, lactose, and whey.
  • Typically, complete avoidance of lactose-containing foods is only necessary for a limited period. You can try to gradually increase lactose.

Dietary changes to maintain energy and protein intake.
Replacing lactase with a supplement.

  • Lactase preparations (Lactaid, Lacrase, LactAce, DairyEase, and Lactrol) are bacterial or yeast beta-galactosidases that will breakdown the lactose that is present prior to it reaching the colon.
  • Take the supplement right before you start eating. If you forget, it can be taken during the meal but might not work as well.
  • The different preparations work differently for each person. Also, every little bit of lactose may not be broken down so you may still have some symptoms.

Maintaining calcium and vitamin D intake.

  • Avoiding milk and other dairy products can cause decreased calcium consumption which may lead to an increased risk for osteoporosis and fractures.

If there is a low level of lactase due to injury or inflammation of the tissue lining the GI tract, treatment of the disease that led to these changes can restore normal lactase activity. This healing process may take months.

Amount of lactose in different foods:

Product Lactose Content (grams)
Milk (1 cup)
Whole, 2 percent, 1 percent, skim
Evaporated milk
Sweetened condensed milk
Lactaid® milk (lactose-reduced)
Goat's milk
Acidophilus, skim
Yogurt, low fat, 1 cup
Cheese, 1 ounce

Cottage cheese (1/2 cup)
Cheddar (sharp)
Mozzarella (part skim, low moisture)
American (pasteurized, processed)
Ricotta (1/2 cup)
Cream cheese
Butter (1 pat)
Cream (1 tablespoon)

Light, whipping, sour
Ice cream (1/2 cup)
Ice milk (1/2 cup)
Sherbet (1/2 cup)




Table from
UptoDate. Adapted from: Scrimshaw NS, Murray EB. The acceptability of milk and milk products in populations with a high prevalence of lactose intolerance. Am J Clin Nutr 1988; 48:1079. Copyright © 1988 American Society for Clinical Nutrition.

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