Lactose intolerance

Lactose intolerance is a common condition in which your body finds it difficult to digest lactose, a sugar found in cows’, goats’ and sheep milk.

Key points

  • Lactose intolerance occurs when your body doesn’t produce enough of the enzyme lactase, which breaks down lactose in your gut.
  • It is not the same as a milk allergy, which has more severe symptoms that can result in anaphylaxis. 
  • Most people with lactose intolerance can tolerate some milk and milk products; you may need to experiment to find what’s right for you.

What causes lactose intolerance?

Some people are more prone to lactose intolerance because of factors such as genetics and certain medical conditions or procedures, for example:

  • Genetic predisposition – lactose intolerance is more common in Asian, Middle Eastern, Mediterranean, South American and African people. It may also be more common in Māori and Pacific people.
  • Gut damage – damage to your gut (small intestine) can occur through surgery or after gastroenteritis (see lactose intolerance after a tummy bug). It can also be caused by conditions such as coeliac disease or Crohn’s disease.
  • Lactase deficiency – this is when your body doesn't produce enough of the enzyme, lactase, which helps digest lactose. Read more about lactase deficiency.

What are the symptoms of lactose intolerance?

You will usually experience symptoms within 30 minutes to 2 hours after eating. These include:

  • flatulence (wind)
  • bloating
  • tummy pain or discomfort
  • nausea (feeling sick)
  • diarrhoea (runny poos).

Symptoms can range from mild to severe depending on the amount of lactose you eat or drink and the amount you can tolerate.

Lactose intolerance or milk allergy?

Lactose intolerance is often confused with milk allergy. These are different conditions. The main differences are:

  • People with lactose intolerance can usually tolerate small amounts of milk products, whereas, in milk allergy, small amounts usually cause symptoms.
  • A milk allergy is related to the protein in milk rather than the lactose. 
  • Most children outgrow milk allergy between 1 and 3 years of age. Lactose intolerance is usually seen after 2 years of age.

Read more about food allergies.

How is lactose intolerance diagnosed?

It’s important to see your GP, rather than diagnose yourself. Cutting out milk products without dietary advice may mean you are missing out on certain nutrients, such as calcium and vitamin D. Your GP will ask questions about your symptoms and when they occur. The condition is normally diagnosed with a lactose tolerance test, a hydrogen breath test, and test for stool acidity.

  • The lactose tolerance test involves not eating prior to the test and then drinking a liquid containing lactose. Blood glucose is measured in the following 2 hours to assess how the person is digesting the lactose.
  • The hydrogen breath test measures the level of hydrogen on a person's breath after drinking a lactose drink. High levels of hydrogen indicate lactose intolerance. This is due to larger amounts of this gas being produced in the bowel because of a failure of the digestive system to break down lactose.
  • The stool acidity test is mainly used for infants whose samples can indicate the presence of undigested lactose.

How is lactose intolerance treated?

There is no way to increase your body's production of lactase, however, many people can avoid the discomfort associated with lactose intolerance by changing their diet. 

Most people with lactose intolerance can cope with a little lactose in their diets. With a bit of trial and error, you will be able to figure out how much you can tolerate. Some people may only need to limit the amount of lactose they eat or drink. A very few people are so severely lactose intolerant that they have to cut out all milk products and be wary any products that contain lactose.

Some people find using lactase products helps reduce their symptoms.

Read more about treatment for lactose intolerance

Looking after yourself on a low-lactose diet

If you are lactose intolerant there are a few important things to consider when reduce or remove products milk products from your diet. 

Keeping a nutritional balance

Milk and milk products are also good sources of calcium. If you are removing or restricting your intact of these products you need to replace these with other foods that contain calcium, such as:

  • lactose-free varieties of milk, yoghurt, ice cream and soft cheeses
  • soy, almond or rice milk that has been fortified with calcium
  • sardines, tofu, soy beans, broccoli, tinned salmon, oranges, rhubarb and spinach.

Also, make sure you get enough vitamin D. Our body normally makes this in response to sunlight but it is also added to fortified milk because many adults don't get enough from sunlight.

Read more about calcium and vitamin D 

Re-introducing lactose into your diet

Completely removing lactose from your diet can actually make symptoms of intolerance worse when you next (intentionally or accidentally) consume milk or milk products. 

Including a little lactose in your diet encourages the growth of gut bacteria which help to breakdown lactose and decreases symptoms.

If you are have removed all milk and milk products from your diet and want to re-introduce these, slowly and regularly increase the amount of milk in your diet. This will allow time for gut bacteria to grow which will with symptoms. 


It may help to see a dietitian to help you work out how to cut out milk products and what to replace them with. Depending on the cause of your lactose intolerance, you may find it helpful to join one of the following support organisations:

Allergy New Zealand 
Coeliac New Zealand 
Crohn’s and Colitis New Zealand

Learn more

The following links provide further information on lactose intolerance. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Lactose intolerance NHS Choices (UK)
Lactose intolerance NIH (US)
Lactose intolerance and the breastfed baby Australian Breastfeeding Association


  1. Lomer, M. C. E., Parkes, G. C., Sanderson, J. D. Review article: lactose intolerance in clinical practice – myths and realities. Alimentary Pharmacology & Therapeutics. 2008;27(93–103).
  2. Best Practice Advocacy Centre New Zealand. Lactose Intolerance. Best Practice Journal. 2007;9 (30-35).

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