Lactose Intolerance

Lactose is the naturally occurring sugar in animal milks e.g. cow, goat and sheep, and can be found in many food products, including:

  • Dairy products (i.e. butter, cream, cheese, yoghurt) and ice cream
  • Biscuits, cakes and chocolate
  • Processed breakfast cereals
  • Salad dressings
  • Packets of instant potatoes and instant soup

Lactose intolerance, also known as lactase deficiency, is a common problem where the body is unable to digest lactose due to an inability to produce enough (or any) of the lactase enzyme in the small intestine.

Lactose intoleranceThere is sometimes confusion between lactose intolerance and a cow milk allergy. A milk allergy is a reaction by the body’s immune system to one or more milk proteins and can be life threatening when just a small amount of milk or milk product is consumed. It is therefore important that the two are not confused. A milk allergy will generally appear in the first year of life, while lactose intolerance occurs more often in adulthood.

People of Hispanic, south Indian, black, Ashkenazi Jewish, American Indian or Asian ethnicity are more susceptible to developing a lactose intolerance than others. Also babies born prematurely are more likely to have a lactase deficiency since lactase levels only increase in the third trimester of pregnancy.

Most people can tolerate some amount of lactose in their diet and a person with lactose intolerance, child or adult, will start to feel uncomfortable anywhere from 30 minutes to 2 hours after consuming food or drink that contains lactose. The symptoms may include:

  • flatulence (wind) or diarrhoea
  • bloated stomach or stomach rumbling
  • stomach cramps and pains
  • feeling sick

There are two types of lactase deficiency:

Primary Lactase Deficiency

This runs in families and will generally develop between the ages of 2 and 20 when your lactase production decreases, often when breastfeeding or bottle-feeding has stopped. However the symptoms may not develop or be noticeable for several years.

Secondary Lactase Deficiency

This is caused by an injury to the small intestine and can occur at any age although is more common in infancy. It can also develop as a result of surgery to your small intestine, some medications or other medical conditions including coeliac disease, gastroenteritis, Crohn’s disease and chemotherapy.

When to seek medical advice

The symptoms of lactose intolerance can be similar to other conditions and so it's important to see your GP for a diagnosis before removing any milk and dairy products from your diet.

Before seeing your GP, keep a diary of what you eat and drink, and what symptoms you experience. Also tell your GP if you notice any patterns or if there are any foods you seem particularly sensitive to.

If your GP thinks you have lactose intolerance, they may suggest avoiding lactose from your diet for two weeks to see if it helps to relieve your symptoms. This will provide further evidence of whether you're lactose intolerant.

They are likely to give you one of the following tests:

Lactose Tolerance Test – after taking a lactose solution drink, a sample of blood is taken from the arm. This is then tested to see how much glucose it contains. If the blood sugar levels rise slowly, or not at all, you will be lactose intolerant. This is due to the fact that your body is unable to break down the lactose in glucose.

Hydrogen Breath Test – following consumption of a lactose-loaded drink your breath is analysed at regular intervals to measure the amount of hydrogen in it. Usually there is very little hydrogen detectable in the breath so if it then contains high levels of hydrogen this is due to the undigested lactose.

Stool Acidity Test – since the above tests involve a large intake of lactose these are generally not given to infants or very young children since it can be dangerous for them. In these instances, a stool acidity test can be used. This will measure the amount of acid in the stool. If there is a high amount of fatty acid, such as acetate present, a lactose intolerance will be diagnosed.

Self help

If you are lactose intolerance, it is important to ensure that you are getting enough calcium in your diet if you have to avoid milk and other calcium rich dairy products. This can be done by increasing your intake of foods such as fish with soft bones (salmon, sardines, pilchards), dark green vegetables (spinach, broccoli, kale) and dried fruits.

Over-the-counter lactase enzyme drops or tablets are now available; these are taken when consuming milk or milk products and can make them more tolerable. In addition, you can now purchase lactose-free and lactose-reduced milk and milk products.

There are a number of alternative foods and drinks available in supermarkets to replace the milk and dairy products you need to avoid. Food and drinks that don't usually contain lactose include:

  • soya milks, yoghurts and some cheeses
  • milks made from rice, oats, almonds, hazelnuts, coconut, quinoa, and potato
  • foods which carry the 'dairy-free' or 'suitable for vegans' signs
  • carob bars

You can also buy cows’ milk containing additional lactase (the enzyme used to digest lactose). This means you still get the nutritional benefits of the milk, but you're less likely to experience any symptoms after consuming it.

Lactose intolerance in children

In general, the same rules about foods to try or to avoid are similar for children and adults. However, if your child is unable to tolerate any lactose, your doctor may refer you to a dietician for nutritional advice because it's important for young children to have certain nutrients in their diet to ensure healthy growth and development.

Sources used in writing this article are available on request

Information contained in this Articles page has been written by talkhealth based on available medical evidence. Our evidence-based articles are certified by the Information Standard and our sources are available on request. The content is not, though, written by medical professionals and should never be considered a substitute for medical advice. You should always seek medical advice before changing your treatment routine. talkhealth does not endorse any specific products, brands, or treatments.

Information written by the talkhealth team

Last revised: 18 March 2018

Next review: 18 March 2021