The truth about food intolerance tests

By Lisa Simon RD and Claire Lynch RD

A growing market, a lack of evidence

Reports of adverse reactions to food have risen in recent decades, with up to 35% of people in Western countries reporting symptoms. Yet well-documented food allergies or intolerances affect only around 3-4%. These unspecified reactions to food types or groups often lead to unnecessary dietary restrictions, reduced quality of life, disordered eating, and poor gut health.

Food intolerance testing is now a booming industry, with companies offering tests that claim to diagnose intolerances by analysing your hair, your electromagnetic field (Vega testing), your muscle responses (kinesiology testing), or the swelling of your white blood cells (the ALCAT test).

Probably the most commonly purchased test is the IgG test, also called the York test – more on this below. These tests are often marketed with the promise of personalised results and quick fixes for common digestive issues such as bloating, diarrhoea, or fatigue.

But how reliable are they?

Food allergy vs food Intolerance: what’s the difference?

First, it’s important to understand that a food intolerance is not the same as a food allergy.

Food allergies involve an immune reaction, typically the production of IgE antibodies, in response to a specific food or food component. These reactions can be serious and potentially life-threatening. Symptoms may include a raised, itchy rash, swelling of the face, tongue and mouth, vomiting, difficulty breathing, and low blood pressure.

IgE food allergy testing and skin prick tests are clinically validated and used in medical settings to diagnose allergies such as peanut or shellfish allergy. An immunologist is required to make the diagnosis.

In contrast, food intolerances are non-allergic responses that do not involve IgE antibodies. They are generally not life-threatening but may cause distressing symptoms after eating certain foods – such as bloating, gas, or diarrhoea. About 85–90% of people with IBS (irritable bowel syndrome) say their symptoms get worse after eating certain foods.

Some companies claim that testing for IgG antibodies can detect food intolerances, but this claim is not supported by evidence.

The problem with IgG testing

IgG antibodies are commonly found in the blood as a normal response to food exposure – they simply indicate that the immune system has encountered a food, not that the body is reacting negatively to it. That is, it measures exposure, not tolerance.

Despite this, many companies use IgG-based testing to generate long lists, sometimes up to 100 foods, that consumers are advised to avoid. This can lead to unnecessary and potentially harmful dietary restrictions.

What about all the other alternative tests?

The British Society of Allergy and Clinical Immunology (BSACI) states that alternative tests (including IgG) have “no proven benefit in the diagnosis of food allergy and food intolerance” and that they may “endanger patients via misdiagnosis.” Similarly, the National Institute of Allergy and Infectious Diseases guidelines do not recommend these tests due to a lack of standardisation or validation.

The risk of unnecessary elimination diets

Cutting out large numbers of foods based on unvalidated tests can lead to nutrient deficiencies and, paradoxically, a decline in gut health. That’s because the gut microbiome thrives on diversity – particularly dietary fibre from a wide variety of plant foods.

A less diverse diet can starve certain beneficial microbes, reducing microbial diversity and potentially worsening gut symptoms. This creates a cycle of restriction, anxiety, and continued digestive distress.

Gut health is not for sale

Tests that claim to analyse the gut microbiome or diagnose food intolerances often come bundled with expensive supplements, “gut repair” protocols, or restrictive diets – all of which lack scientific backing. At best, these are unnecessary; at worst, they may worsen symptoms and cause psychological distress.

Stress and anxiety themselves negatively impact the gut-brain axis, altering gut function and microbial diversity. The nocebo effect, where believing a food will cause harm makes symptoms worse, is also a real concern in this context.

What does work?

There is strong evidence that a varied, fibre-rich, plant-predominant diet supports a healthy gut microbiome. Feeding your gut microbes with a diverse range of plant foods helps them produce short-chain fatty acids, which have wide-ranging health benefits for the gut, brain, and beyond.

Working with a dietitian

If you’re experiencing ongoing digestive symptoms or suspect a food intolerance, working with a registered dietitian is the safest and most effective approach. Rather than relying on unvalidated commercial tests, a dietitian will guide you through an evidence-based process – typically starting with a detailed food and symptom diary to identify patterns and potential triggers.

In some cases, a structured programme of elimination and reintroduction may be advised. This is considered the gold standard for identifying true intolerances and ensures that unnecessary dietary restrictions are avoided.

Some of the most common food intolerances seen in clinic include:

• Lactose intolerance – dairy products
• Non-coeliac gluten/wheat sensitivity – wheat, rye, barley, and sometimes oats
• Histamine intolerance – aged or fermented foods, and certain fruits, vegetables and fish
• FODMAP intolerance – fermentable carbohydrates found in a wide range of foods, which can trigger symptoms in people with IBS

For those with irritable bowel syndrome (IBS), the low FODMAP diet, when used short-term and under professional guidance, can be a helpful tool for identifying triggers and improving symptoms without compromising nutritional adequacy or gut health. It’s typically recommended only if simpler dietary strategies haven’t been effective.

The bottom line

Food intolerance tests sold directly to consumers are not clinically validated and are not recommended. They can lead to unnecessary worry, dietary restrictions, financial cost, and poorer gut health.

If you’re experiencing new or ongoing digestive symptoms, speak to your GP. Then, if needed, seek support from a dietitian trained in managing gut health. Evidence, not expensive tests, should guide your next steps.