Lactose Intolerance – What is it? How Is It Diagnosed? How Do I Manage It?

Lactose intolerance is a common gastrointestinal complaint. Find out what lactose intolerance is and how to manage it safely.

milk for lactose intolerance article

What is Lactose?

Lactose is a type of sugar that is naturally found in milk and milk products such as yoghurts, cheese, ice cream and chocolate.

Lactose is broken down by an enzyme called lactase, which is produced in the lining of the small intestine. Lactose is then absorbed into the body (1).

What is Lactose intolerance?

Lactose intolerance is an impaired ability for the body to breakdown lactose. This may be due to a lactase enzyme deficiency which can be present from birth (congenital lactase deficiency) or may be present itself in adulthood due to a reduced production of lactase by the gut.

A reduced production of lactase in the gut occurs in people with coeliac disease, inflammatory bowel disease (such as Crohns disease) or gastritis. In these conditions, the gut lining is damaged and unable to make lactase to break down lactose.

In most conditions, the gut is only temporarily damaged, individuals are usually able to go on to manage lactose again, i.e. in gastritis or in coeliac disease (1, 2 ).

Symptoms and diagnosis

If lactose containing foods are eaten in those with lactose intolerance, lactose can build up in the intestines. The built up lactose attracts water molecules into the gut – causing diarrhoea. Whilst gut bacteria works to break down the lactose – producing gas.

Symptoms of lactose intolerance;

  • Diarrhoea
  • Bloating
  • Abdominal pains
  • Stomach cramps
  • Flatulence
  • Nausea

These symptoms are very similar to many other digestive conditions and therefore a number of tests need to occur to confirm your diagnosis. Failure to do this may lead to you not being diagnosed correctly and you could suffer with some serious long-term health conditions (1, 2 , 3 ).

Diagnosis can be done by your doctor via a hydrogen breath test. This test measures how much gas (hydrogen) is produced by your gut bacteria when you have lactose. A higher reading can confirm lactose intolerance.

Lactose intolerance can also be confirmed by following a lactose free diet for around 2-4 weeks and monitoring if your symptoms are relieved. Confirmation of lactose intolerance would then be made by reintroducing milk based foods into your diet and assessing if your symptoms return. The best way to assess this is via a food and symptom diary under direction of a dietitian (1, 2 , 3 ).

Lactose Intolerance vs Milk Allergy

We now know lactose intolerance occurs due to a lactase deficiency. However, a milk allergy is when our bodies produce an immune reaction to a cow’s milk protein present in milk products causing eczema and gut symptoms.

This usually presents itself in childhood on exposure to either formula milk, cow’s milk as a toddler or in more sensitive cases breastmilk from a mother who has cow’s milk in her diet. The confusion between the two arises as the treatment is also a milk free diet however the cause is the symptoms is very different (3 , 4).

Can You Have Any Lactose?

In short, yes!

The amount of lactose tolerated varies between all adults. However, those with a lactose intolerance can manage around 12g of lactose a day. This is the same as around 200mls of milk (a small glass) or a small tub of yoghurt (125g).

To find out what your ‘tolerance’ level is, start by reintroducing a small amount and over several days increase it slowly until you find your symptoms are flared up.

What Does This Mean For My Diet?

It is essential that you replace lactose containing foods with lactose free alternatives in order to make sure that you are not missing out on the nutrition provided from the dairy food group – calcium, protein and vitamin B12 .

Many lactose free products are now widely available for alternatives to milk, yoghurts, cheese and butter. These are usually made from oats, soya, rice, coconut, cashews, hazelnuts or almonds, so it is important to try a range of products to see which one you like the taste of the best. Ensure that the product you choose is fortified with calcium and vitamin B12. Ensure that you are having around 2- 3 portions of lactose free alternatives a day to meet your calcium requirements (see BDA diet sheet below for further details).

Unlike a milk free diet for those with an allergy, those with a lactose intolerance can have small amounts of lactose as previously discussed. There are also dairy foods which, you may be surprised to find, have hardly any lactose in them at all –  cheddar, feta, mozzarella, edam, brie, goats cheese, camembert, pecorino, Swiss cheese, blue cheese, butter, margarine, sour cream, crème fraiche and dark chocolate (2 ,4,5 ).

Please note, those with coeliac disease have higher daily calcium requirements but you should be under a dietitian who will help you with meeting this (1, 2 , 3 , 4).

Bottom Line

If you have any of the symptoms above, please seek advice from your GP. After they rule out other digestive health issues, you may be offered a hydrogen breath test or you can seek out a dietitian to support you through a lactose restriction and reintroduction diet.

If you have lactose intolerance, then ensure your calcium and vitamin B12 levels are sufficient. Depending on the cause of your intolerance, you may overcome lactose intolerance in the future. However, all those with lactose intolerance can tolerate small amounts of lactose in their diet.


Article Written Dietitian Olivia Done

Edited & Reviewed by Dietitian Kirsten Crothers


For more information:

Coeliac UK: Coeliac Disease and Lactose Intolerance

BDA Factsheet on Milk allergy and Lactose intolerance



  1. Truby,H., Hart, K. and Dart,J. (2015) Malabsorption. In J. Gandy (Ed) The manual of dietetic practice (5th edition) (pp. 420-425). Oxford, United Kingdom. John Wiley and Sons Ltd.
  2. National and Dietetic Resources UK (2014) Milk-free Zone information leaflet

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