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The question

I love my cheese - but sometimes (not always) I get an upset stomach. Does that mean I'm lactose intolerant?

The answer

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Lactose intolerance is the inability to digest lactose, a sugar found in milk and other dairy products. It occurs when the body doesn't make enough lactase, an enzyme found in the lining of the small intestine, that digests and breaks down lactose.

When undigested lactose moves into the colon, it interacts with normal intestinal bacteria which can result in the uncomfortable symptoms of lactose intolerance such as bloating, gas, cramps, and diarrhea.

Symptoms usually occur about 30 minutes to 2 hours after eating or drinking milk products and vary in severity from person to person.

Close to 75 per cent of adults have some form of lactose intolerance with those of African, Asian, Hispanic, and Native American descent being at higher risk. Lactose intolerance is divided into primary and secondary types:

Primary lactose intolerance develops due to a decrease in lactase production from early childhood. This form usually presents itself in the late teens to early adulthood.

Secondary lactose intolerance is from injury (from infection such as gastroenteritis or illnesses such as Celiac disease or Crohn's disease) to the small intestine lining where the lactase enzyme is found. If this is the case, resolution of the infection and healing of the lining or treatment of the underlying disorder may restore lactase production and reduce symptoms.

In your case, your symptoms of intermittent upset stomach may very well be due to lactose intolerance. Your symptoms may occur now and then because most people with lactose intolerance are usually able to tolerate a small amount of lactose. Certain types of milk products have lower levels of lactose and as such, can be digested more easily than others. Examples of milk products with lower lactose levels include: buttermilk, hard cheeses and yogurt. This may be why despite your love of cheese, you aren't always affected by symptoms.

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Does your upset stomach occur only after ingesting milk products? Is it related to stress? Do other types of food such as wheat or fatty foods cause the stomach upset? Are you having any alarm symptoms such as blood in stool, weight loss – which may mean a more serious underlying cause? The answer to these questions will help guide you and your doctor towards a diagnosis.

While there is no known way to prevent lactose intolerance, symptoms can generally be managed with dietary changes. Some tips include:

1. Experiment with different milk products as not all have the same amount of lactose (hard cheese, yogurt)

2. Use lactose free/lactose reduced products

3. Read food labels and watch our for hidden lactose: baked goods, breads, processed foods and liquid meal replacements are prime examples.Lactose can also be found in medications, so let your pharmacist know about your stomach issue.

If despite changing diet you are still experiencing symptoms, your doctor may suggest over-the-counter lactase enzyme supplements to be taken with milk products to help with digestion.

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Finally, talking with a dietitian may be helpful in planning a balanced diet that provides alternative sources of calcium and vitamin D which are important for maintaining bone strength.

Send family doctor Sheila Wijayasinghe your questions at She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

Read more Q&As from Dr. Wijayasinghe.

Click here to see Q&As from all of our health experts.

The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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