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Lactose intolerance

Published on May 10, 2024 at 8:00 / Updated on May 25, 2024 at 8:00

Lactose is a naturally occurring sugar found in milk and dairy products. It is broken down in the small intestine by an enzyme called lactase. Lactose intolerance occurs when a person does not produce enough lactase to properly digest lactose.

In individuals with lactose intolerance, foods that contain lactose are often poorly digested, leading to the fermentation of undigested lactose in the large intestine (colon). As a result, the following symptoms may occur within 30 minutes to 2 hours of ingesting lactose:

  • Bloating
  • Stomach pain or cramps
  • Gurgling in the belly
  • Gas
  • Loose stools or diarrhea
  • Vomiting

Lactose intolerance is not the same as milk allergy, which is an abnormal response by the body's immune system to the proteins found in milk.

Causes and triggers

Lactose intolerance is common in adults, and occurs more often in First Nations and in people of Asian, African, and South American descent.

It is usually genetic (inherited), and generally develops in adolescence or adulthood. Diagnostic tests are available, but a trial period of a lactose-free diet is often all that is needed to make the diagnosis.


There is no cure for lactose intolerance. However, certain measures may be taken to limit symptoms and improve your well-being.

You can choose to limit or avoid dairy products. It should be noted that many processed foods (e.g., bread, desserts, dressings and sauces, instant oatmeal, sausages and cold cuts) contain lactose. Reading ingredient lists and food labels is recommended to identify lactose-containing products. The most common sources of lactose are:

  • Milk
  • Cream
  • Yogurt
  • Cheese
  • Butter
  • Ice cream

If you decide to avoid foods that contain lactose, make sure you get enough calcium in your diet (e.g., lactose-free dairy products, calcium-rich dairy-free products) or consider taking calcium supplements. For more information, speak to your health care professional.

To help prevent symptoms associated with lactose intolerance, you may also choose to take lactase supplements (e.g., Lactaid). These tablets should be taken just before eating dairy, and the dose may be adjusted to the amount of lactose ingested. If you forget to take it before your meal, you can take the tablet with your meal, but its effect may be reduced. The effectiveness of these products varies from person to person. You may therefore still have symptoms.

When should I see a medical professional?

Do not hesitate to see a health care professional if you develop symptoms suggestive of lactose intolerance after eating dairy products.

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