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HealthInfo Canterbury

Lactose intolerance

Lactose is a natural sugar found in milk and some milk products such as yoghurt and ice cream. Lactose is usually broken down in your small intestine by an enzyme called lactase. Lactose intolerance happens when your small intestine does not make enough lactase.

When this happens, the lactose passes through to your large bowel. The bacteria that live in your large bowel break down the lactose. This causes symptoms such as:

These symptoms usually begin 30 minutes to two hours after eating or drinking foods that contain lactose.

Lactose intolerance is not the same as milk allergy

Milk allergy is an allergic reaction to the protein in milk and is more common in babies and young children than adults. It usually disappears as children grow older.

If you have a milk allergy, you need to avoid all milk and milk products. If you have a lactose intolerance, you can usually eat cheese, and small amounts of milk and yoghurt.

How common is lactose intolerance?

Lactose intolerance is not common in babies. Most lactose intolerance starts during childhood or the teenage years. It is more common in Asian, Middle Eastern, Mediterranean, South American and African people. It may also be more common in Māori and Pacific people.

People sometimes get lactose intolerance after gastroenteritis (tummy bug). This can also happen due to damage to the small intestine caused by diseases such as coeliac disease. This type of lactose intolerance usually disappears once the infection or disease has been treated.

Diagnosing lactose intolerance

If you think you might be lactose intolerant, talk to your doctor or practice nurse. They will ask you about your symptoms and your health and lifestyle. If it's possible that you are lactose intolerant, you will need to avoid lactose-rich foods for two weeks.

Lactose-rich foods include:

  • fresh cow, goat and sheep milk
  • powdered, evaporated, and long-life milk
  • buttermilk
  • sweetened condensed milk
  • yoghurt
  • custard
  • ice cream
  • creamy pasta sauces and white sauces
  • sour cream and crème fraîche
  • soft unripened cheeses such as ricotta, cottage, cream cheese, and mascarpone.

You don't need to avoid bread, biscuits or cake that contain milk. The amount of milk in these foods is not enough to cause symptoms.

If your symptoms don't get better after two weeks, then you are not lactose intolerant. You should start eating normally again and see your doctor.

If your symptoms get much better after two weeks, then you know lactose is a problem.

Lactose intolerance can also be diagnosed by breath hydrogen testing.

Breath testing is not available in the public health system, but you may opt to pay for it privately. You can search for a company that does breath testing in the Yellow pages.

On the next page: How to manage lactose intolerance

Written by HealthInfo clinical advisers. Endorsed by Nutrition and Dietetics, Christchurch Hospital. Last reviewed August 2018. Last updated March 2019.


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Review key: HILAC-250023