Do you need to buy a food intolerance test?

I’m a gastroenterology dietitian. I often see patients who have done food intolerance tests and think they’re intolerant to a long list of foods. I then have to be the bearer of bad news and let them know that the online intolerance tests are essentially scams and they don’t show you anything.

I can appreciate having uncomfortable symptoms like loose stools or stomach cramps and wanting to find an answer as to what’s causing them. But forking out hundreds of pounds for an intolerance test isn’t going to help.

person holding their stomach

It’s important we clear something up first.

What’s the difference between an allergy and a food intolerance?

A food allergy is when your body has a negative overreaction to a certain food. It sees that food as a threat and triggers a release of chemicals.

Food allergies can be mild, to life threatening.

Symptoms of a food allergy include:

  • ·         Coughing, wheezing or breathlessness
  • ·         Swelling of the face, lips and eyes
  • ·         Feeling sick and/or vomiting
  • ·         Diarrhoea
  • ·         Feeling lightheaded or dizzy
  • ·         Stomach pain
  • ·         Runny nose or sneezing

An example of this is a peanut allergy. Some people are so sensitive that even the smell of a peanut can send them into anaphylactic shock.

monkey nuts

A food intolerance is where your body isn’t able to digest a certain food very well or a certain food irritates the gut.

Symptoms of a food intolerance can be:

  • ·      Stomach cramps and pain
  • ·      Diarrhoea
  • ·     Headaches
  • ·      Feeling sick
  • ·      Bloating
  • ·      Farting

A common example of this is lactose intolerance. If you have lactose intolerance and eat something containing lactose, you may be shortly rushing to the toilet.

cheese platter

How do you test for a food intolerance? (according to the internet)

An internet search will have you believe that sending a hair or blood sample will test for all your food intolerances. But that’s simply not the case.

The York test is a common one I’ve seen with patients in clinic. For the York test you do a finger prick blood test and get ‘results’ saying what you had high reactivity to. You then eliminate these foods from your diet, and everything is solved.

These tests look for a protein called IgG or immunoglobulin G. This is a common antibody that helps protect us from infection. The tests say that an increase in IgG, in reaction to certain foods, suggests an intolerance.

But in reality, all these tests show you are the foods you commonly eat. An increased IgG in relation to a certain food is completely normal, and only shows you’ve recently had exposure to the food i.e you've eaten it lately. 

brown hair

Tests that ask for hair samples are also not based in science. There’s nothing in your hair that would tell if you had a food intolerance or not. Hair is slow growing, and once it reaches the skin surface, i.e. the hair you can see on your body, it’s dead. So, it’s not much use to tell us what's going on in your gut.

So how do you really test for a food intolerance?

I’m afraid the real ways to test for food intolerances aren’t as snazzy as a blood test or hair sample.

Breath tests:

A breath test can look for lactose or fructose intolerance. Lactose is the sugar naturally found in dairy products, while fructose is the sugar naturally found in fruits, vegetables, and honey.

If you’re in the UK, this test can be done in the NHS but is less common and only done at particular hospitals.

These breath tests work by analysing the amount of hydrogen gas you breathe out. The more hydrogen you breathe out, the more likely you’re not able to digest the sugar.

fruit basket with pineapple, mango, grapes, kiwi,  apples, and plums

This is because if the sugar isn’t digested as normal it’ll reach our large bowel where the bacteria that live there digest it, and they produce hydrogen gas a result. We then breathe out all this extra hydrogen.

Breath tests only work for sugars and show that we don’t digest them well – i.e. we’re intolerant.

Elimination diet:

A more common way to test for an intolerance is to do an elimination diet.

This is where you stop eating the food you think is causing problems and see if your symptoms resolve. After a few weeks you can then start eating the food again and see if the symptoms come back. If they come back, then it’s likely that it’s the food that was triggering you.

This only works with one food at a time, as if you remove multiple things at once you won't know what’s led the symptom improvement. It also reduces the risk of an unbalanced diet as if you cut out lots of things you’re likely to be missing out on key nutrients.

It’s important to note that you should only do a reintroduction of the food if it’s an intolerance and not an allergy, as an allergy can be life threatening.

glass of milk

It’s not worth spending lots of money on an intolerance test, as they’re not showing you the truth. The websites may seem convincing but unfortunately, it’s all a sham.

If you think you’re allergic or intolerant to something, contact a healthcare professional.

Key points:

  • A food allergy is where the body reacts negatively to a certain food, and it can be life threatening.
  • A food intolerance is where you’re not able to digest a certain food properly.
  • The internet will have you believe you can test for an intolerance with a blood or hair sample, but this isn’t the case.
  • The only way to test for an intolerance is to do an elimination diet or hydrogen breath test.

Thanks for reading!

Bye for now 👋


Food allergy: and


  1. This is a very insightful post!


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