The truth about food intolerance tests

There are a growing number of companies claiming to be able to diagnose food intolerances by analysing your hair, or stool samples, or to tell you the composition of your gut microbiome and how you can improve it.

A food allergy is serious and potentially life-threatening. With the majority of food allergies, the body will produce IgE antibodies in response to ingestion of a trigger food, and that is when an allergic reaction will occur. IgE food allergy tests are clinically validated and are used in the hospital setting. For example, when testing for a peanut allergy.

A food intolerance is when a non-life-threatening response occurs. For example, gastrointestinal symptoms such as bloating, wind and diarrhoea. Food intolerance tests look for IgG antibodies, with companies claiming that a positive test means an intolerance to that specific food. What actually happens is that as IgG antibodies are abundant in the body, their presence is likely a normal response of the immune system to exposure to food, not an indicator of intolerance. It is not clinically validated for diagnosing food intolerances, as studies supporting the use of this test are fundamentally flawed.  

These tests are expensive and will often yield results showing a long list (up to 100 different foods) of foods to avoid in order to prevent gastrointestinal symptoms. If this list is then followed, there is the very real risk of that person not only becoming deficient in a number of nutrients, but ironically causing their gut microbiome to become less diverse, which will then lead to worsening of symptoms.

When it comes to the gut microbiome, diversity is key. With a varied plant-based diet containing different types of fibre, the gut microbes will be fed and will produce short chain fatty acids. These then exert positive health benefits throughout the body, including the brain, as they are able to cross the blood-brain barrier. The gut and the brain are intrinsically linked, so the healthier the gut, the healthier the brain, and vice versa. Each gut microbe will thrive on a different food, or food group, so if any of these foods are eliminated, that particular microbe will eventually die out, leading to a less diverse, less healthy gut environment.

These tests can also heighten anxiety and stress, and we now know that this directly impacts our gut microbiome, therefore again, causing a reduction in diversity. In addition, these tests are expensive, and people are often sold a number of supplements after receiving their results to assist gut repair, none of which are evidence-based or effective.

Bottom line

Do not waste your time or your money on these tests. The best way to improve the gut microbiome, and therefore improve gut health, is to eat a diverse plant-based diet. Eliminating foods or even entire food groups should be avoided, however, for some people with irritable bowel syndrome, dietetic supervision can help to identify potential food triggers, and then an evidence-based approach can be adopted to help manage and improve symptoms. It is very important to see your GP straight away if you have any new bowel symptoms, before making any dietary changes.