How IBS can be mistaken for food allergy

By March 18, 2020 FODMAP, Health, IBS

This article was written by Marianne Williams, a Registered Dietitian in the UK, and refers to experiences in her clinic which is not affiliated to mySymptoms. The opinions expressed in this article are the author’s own.

Irritable Bowel Syndrome (IBS) is a chronic and debilitating condition which can cause a myriad of distressing gut symptoms. However, the IBS symptoms of abdominal pain, wind, bloating, reflux, nausea and diarrhea or constipation can also be symptoms of food allergy. This can make the correct diagnosis very difficult. Indeed, in our last clinical audit we found that 8% of our IBS patients were in fact allergy patients who had been wrongly diagnosed.

Food allergy is still comparatively rare affecting 1.2 – 3.2% of the adult population. Allergy involves the immune system, while food intolerance does not, and is a completely different condition. For allergy we often use a diet which eliminates one whole food group e.g. a dairy free diet, while for food intolerance you might use a diet such as the Low FODMAP Diet. This is often an area of confusion for both the general population and the medical profession and can lead to the use of inappropriate and frustratingly ineffective diets.

There is increasing research to indicate that there may be a subset of ‘IBS-type’ patients, particularly those with a history of allergic disease e.g. asthma, eczema, hay fever, for whom food allergy may be more relevant. Food allergy comes in two forms: ‘IgE’ and ‘non-IgE’ which further complicates the picture:

  1. IgE allergy generally shows immediate reactions e.g. peanut allergy. Patients can be tested using skin prick tests or specific IgE blood tests. These tests are normally conducted in a clinical environment at a specialist allergy centre.
  2. Non-IgE allergy shows delayed reactions from 1-24 hours. This type of allergy is common in patients suffering predominantly from gut symptoms. For this type of allergy there are no known tests – no matter what you see advertised on the high street or in magazines. Diagnosis is made using food elimination followed by food reintroduction.

It can be very difficult to follow an allergy diet and it is vital that all sources of the suspected food including cross contamination are avoided if one is to obtain an accurate diagnosis. Part of the diagnosis is the reintroduction of the food to see if symptoms reoccur. However, in order to prevent dangerous reactions and malnutrition, it is vital that this is done under the supervision of a suitably trained allergy specialist – either a doctor or dietitian. You can ask your GP for a referral to your nearest allergy trained dietitian or to the nearest specialist allergy centre.

Please remember that true food allergy is still relatively rare in adults. For the majority of our IBS patients, food intolerance is normally relevant and for this the Low FODMAP Diet is often the answer.

Marianne Williams

Marianne Williams

Marianne is a Registered Dietitian in the UK and was awarded ‘Dietitian of the Year’ in 2012. Marianne set up the first NHS primary care dietetic-led gastroenterology clinic in the UK in 2011 specialising in dietary treatment for adults with IBS and gastrointestinal allergy.

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