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Lactose intolerance is the inability to digest lactose.

Lactose intolerance is the inability to digest lactose.
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Lactose intolerance

7-minute read

What is lactose intolerance?

Lactose intolerance is the inability to digest lactose, the main sugar found in milk and in dairy products made from milk, including yoghurt, ice cream, soft cheeses and butter. It is sometimes referred to as dairy intolerance and is rarely serious.

Lactose intolerance occurs when the body does not produce enough lactase enzyme to break down the lactose. Instead, the unabsorbed lactose moves on to the large intestine where it’s digested by bacteria using their own enzymes. The gases created in this process can produce symptoms.

Lactose intolerance is different from milk allergy, which is an immune reaction to milk or milk products that can be serious. An allergic reaction to milk or milk products can cause symptoms such as an itchy skin, rash, swelling of the lips or difficulty breathing. Seek medical advice urgently if you suspect a serious allergic reaction.

Since a severe allergic reaction should always be treated as a medical emergency, it is also useful to know about first aid treatment for anaphylaxis.

What are the symptoms of lactose intolerance?

The symptoms of lactose intolerance include:

The symptoms usually come on 30 minutes to several hours after eating or drinking products that contain lactose. Drinking just 1 cup of milk can cause symptoms.

CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

What causes lactose intolerance?

Lactose intolerance occurs because the body is not producing enough lactase, which is the enzyme that breaks down lactose in the small intestine.

Most people are born with the ability to break down lactose but a range of factors increases the risk of developing lactose intolerance later in life.

Genetic factors

Some people have lactose intolerance because they have a genetic difference that reduces the effectiveness of their body in being able to break down lactose. The tendency to produce less lactase enzyme with age is more common in people of Asian, African, South American, Southern European and Australian Aboriginal heritage than in people of Northern European descent.

Medical factors

Lactose intolerance can be caused by diseases that affect the small bowel, such as coeliac disease or Crohn’s disease.

It can also be caused temporarily by gastroenteritis, which can strip the intestines of lactase for a week or 2, a parasitic infection, which can temporarily reduce lactase levels, or lack of iron in the diet, which can interfere with lactose digestion and absorption.

Some people find that their ability to tolerate lactose goes down as they get older.

When should I see my doctor?

If you think you or someone in your care might have lactose intolerance, it’s important to see your doctor for a diagnosis and appropriate treatment.

ASK YOUR DOCTOR — Preparing for an appointment? Use the Question Builder for general tips on what to ask your GP or specialist.

What are the tests for lactose intolerance?

Lactose intolerance is usually diagnosed by doing a trial run. If you avoid lactose for a few weeks and your symptoms improve, but when you reintroduce lactose your symptoms return, then you probably have lactose intolerance.

Another simple test is to compare whether you can tolerate lactose-free milk but not ordinary milk.

Other tests that are sometimes done include breath tests and blood glucose tests to see if your body is producing enough lactase.

Occasionally, people with severe symptoms where the diagnosis is not clear will have a biopsy of their small intestine. In this test, a sample of bowel wall is taken during an endoscopy (when a camera is passed down into the intestines). This is an invasive test and is not commonly used.

How is lactose intolerance treated?

The main treatment for lactose intolerance is to reduce the amount of lactose in the diet. Most people with lactose intolerance do not need to eliminate dairy foods from their diet altogether. Many of these foods do not contain large amounts of lactose and are a good source of calcium. For example, most cheeses contain virtually no lactose and are usually well tolerated. Yoghurt is also generally well digested since it contains bacteria that ferment (or consume) the lactose.

If you are lactose intolerant and also suffer from irritable bowel syndrome (IBS), you may be following a low FODMAP diet. See here for more information on lactose and dairy products on a low FODMAP diet.

A few people have such severe lactose intolerance that they have to avoid certain medicines because they contain lactose. It’s best to speak with your doctor or pharmacist if this is the case.

Lactose intolerance can be temporary, and it may be possible to gradually reintroduce milk and dairy products over time if you have had to reduce them in your diet.

Tips to avoid lactose

Most people with lactose intolerance can consume up to 250ml (1 glass) of milk each day, if you consume it in small amounts throughout the day along with other foods.

You may also need to manage how you eat dairy foods to reduce the possibility of symptoms.

For example:

  • Drink milk with other foods and not on an empty stomach.
  • Distribute milk intake into small serves spread out over the day.
  • Build up your tolerance by starting small and gradually increasing your milk consumption. Most people with lactose intolerance can tolerate ½ cup of milk at a time.
  • Choose regular fat milk as it contains less lactose than low fat or skim milk.
  • Choose yoghurt or cheese low in lactose, as these are often better tolerated than milk.
  • Buy drops from your pharmacy to put in milk to make it easier to digest. Talk to your doctor about the best product for you.
  • Watch out for lactose in processed foods such as biscuits and cakes, cheese sauce, cream soups and custards. Check labels for the terms ‘milk solids, non-fat milk solids, whey and milk sugar’.

Tips to get enough calcium

It’s important to consume enough calcium every day. Most adults need at least 1,000 mg of calcium every day — more if you are an older or a pregnant woman.

Soy products with added calcium do not contain any lactose and can be a substitute for dairy products.

Other foods are good sources of calcium include:

  • soy, almond and rice milk, although these are often lower in calcium than milk
  • broccoli, tinned salmon, oranges, pinto beans, rhubarb and spinach

Complications of lactose intolerance

If you consume lactose, you may get uncomfortable symptoms but it will not damage your bowel. There are no long-term complications of lactose intolerance.

Resources and support

If you suspect you have lactose intolerance, it’s wise to speak to a doctor or a dietitian. You can find an Accredited Practising Dietitian on the Dietitians Australia website.

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Last reviewed: November 2020

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