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 about lactose intolerance

  1. Lactose intolerance occurs when your body doesn’t produce enough of the enzyme lactase, which breaks down lactose in your gut.
  2. It is not the same as a milk allergy, which has more severe symptoms that can result in anaphylaxis
  3. Most people with lactose intolerance can tolerate some milk and milk products. You may need to experiment to find what’s right for you.
  4. If you think you are lactose intolerant, see your GP for a diagnosis before taking milk products out of your diet.
  5. 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. 

What causes lactose intolerance?

Lactose intolerance occurs when your body doesn’t produce enough of the enzyme lactase, which breaks down lactose in your gut. Lactase is produced and present in your gut lining. Lack of lactase can be due to a number of causes:

  • Inherited forms of lactase deficiency – lactose intolerance is more common in Asian, Middle Eastern, Mediterranean, South American and African people. It may also be more common in Māori and Pasifika 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.

What are the symptoms of lactose intolerance?

The symptoms of lactose intolerance are usually non-specific and vary between people. 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. As these symptoms are non-specific and can be caused by other conditions, such as irritable bowel syndrome or milk protein intolerance, see your GP for a diagnosis before taking milk products out of your diet.

Lactose intolerance or milk allergy?

Lactose intolerance is often confused with milk allergy. These are different conditions.

  • 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 6 years of age.

Read more about cows’ milk allergy or lactose intolerance.

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 miss out on certain nutrients, such as calcium and vitamin D. Your GP will ask questions about your symptoms and when they occur. It’s a good idea to keep track of what you eat and drink by keeping a diary before seeing your GP.

The condition is usually diagnosed with a trial of taking lactose out of your diet to see if your symptoms disappear. It is then re-introduced at a later stage to find out how much lactose you can tolerate.  

There are other tests available to diagnose lactose intolerance, such as a lactose intolerance test or hydrogen breath test. However, these are not sensitive or specific enough to provide an accurate diagnosis, so they are not widely used and rarely needed.

Your GP will let you know if you need further tests.

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.

What are the complications of lactose intolerance?

Milk and other dairy products contain protein, calcium and some vitamins. These are important for development of strong and healthy bones. If you remove milk products completely from your diet, you may be at risk of conditions such as:

  • osteopenia (weak bones due to bone loss)
  • osteoporosis
  • malnutrition.

If you are concerned about cutting out milk products and what to replace them with, ask your doctor to refer you to a dietitian.

Looking after yourself on a low-lactose diet

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

Keeping a nutritional balance

Milk and milk products are good sources of calcium. If you remove or restrict your intake of these products you need to replace them 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. Your 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 that help to breakdown lactose. This decreases symptoms when you are exposed to lactose.

If you 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 help limit symptoms. 

What support is available with lactose intolerance?

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 NZ
Coeliac NZ
Crohn’s and Colitis NZ

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, UK
Lactose intolerance Patient Info, UK
Lactose intolerance NIH,US
Lactose intolerance and the breastfed baby Australian Breastfeeding Association

References

  1. Investigating the gut: Lactose intolerance BPAC, NZ, 2010
  2. Lomer MCE, Parkes GC, Sanderson JD Review article: lactose intolerance in clinical practice – myths and realities Alimentary Pharmacology & Therapeutics. 2008;27(93–103).
  3. Lactose intolerance BPAC, 2007, NZ

Reviewed by

Dr Helen Kenealy is a geriatrician and general physician working at Counties Manukau DHB. She has a broad range of interests and has worked in a variety of settings including inpatient rehabilitation, orthgeriatrics and community geriatrics.

cow' milk allergy

Credits: Health Navigator Editorial Team. Reviewed By: Dr Helen Kenealy, geriatrician and general physician, Counties Manukau DHB Last reviewed: 20 Jul 2020