Can a Test Tell You Which Foods to Avoid? The Facts About Food Intolerance Testing

What is a food intolerance?

A food intolerance occurs when your body has difficulty digesting or breaking down certain foods or food components, and this results in unpleasant symptoms. One example is lactose intolerance, where the body can't break down lactose, the naturally occuring sugar in milk. The undigested lactose travels through the gut, typically causing bloating and

Food intolerance is not the same as food allergy

A food intolerance is different from a food allergy, because it does not involve the immune-system. For that reason, food intolerances are not expected to cause anaphylaxis (severe, rapid, and potentially life-threatening allergic reactions).

Symptoms of a food intolerance are often dose-dependent and may appear gradually, usually a few hours after eating. They can include:

• Bloating and gas
• Abdominal pain or discomfort
• Diarrhoea or constipation
• Nausea
• Sometimes headaches or tiredness

The term food intolerance is broad, and the underlying causes often vary. They may include difficulty digesting certain sugars, such as lactose, or sensitivity to fermentable carbohydrates, such as FODMAPs.

What type of food intolerance tests are available

There are many commercially available tests which claim to identify food intolerances. They can look convincing and may be presented as healthcare products, use scientific sounding language and provide detailed reports.

It is therefore understandable that people may see them as a legitimate way to investigate symptoms.

However, most have not been scientifically validated for diagnosing food intolerance. The results can be misleading and might lead people to worry, or to avoid foods unnecessarily, without showing those foods caused their symptoms.

Common tests include:

IgG test: These measure food-specific IgG antibodies, sometimes including IgG4 antibodies. Higher levels are often claimed to show an intolerance, but IgG antibodies are common in healthy people and usually reflect exposure to a food, rather than being the cause of symptoms.

Hair analysis: A hair sample is sent to a laboratory and matched against a food database. There is no scientific evidence that hair can identify food intolerances.

Muscle testing (kinesiology): A practitioner tests muscle strength while you hold, or are near a food. Research does not support this as a way to identify intolerances; results can be influenced by unconscious movements, expectations or bias.

Electrodermal testing (Vega testing): This involves measuring electrical signals in the body by using a probe on the skin, while foods are held nearby or placed in a circuit. It is unproven and lacks scientific validity for diagnosing food intolerances. Results can be affected by skin moisture, pressure and how the equipment is handled.

Cytotoxic testing (including ALCAT): This test mixes a blood sample with foods and intolerance is detected if there are changes in white blood cells. There is little scientific evidence to show that changes reliably indicate food intolerance.

Why food intolerance testing feels appealing

If you're experiencing symptoms that you think are caused by food, you might have considered taking a food intolerance test. These are appealing because they claim to identify your triggers, testing your response to around 200 foods, for around £100-200.

If your symptoms are unpredictable or affecting daily life, the chance of getting some answers and an action plan is appealing. And, almost everyone knows someone who says they felt better after cutting something out. Personal stories can be powerful, but they do not prove that the test identified the cause.

Feeling better can reflect changes in eating patterns, for example, having more regular meals or fewer highly processed foods, or from natural fluctuations in symptoms.

Practical steps

If you think you may have a food intolerance, there are some evidence-based ways to help you identify if food is playing a role.

Keep a food and symptom diary: You may be asked to write down everything you eat and drink and record any symptoms, their severity, and the timing over 2-4 weeks. This can help to identify patterns which you can discuss with a healthcare professional.

Try a supervised elimination diet and structured reintroduction: This involves the temporary removal of one food or food group and then reintroducing it in a planned way. This can help to show if a food is triggering symptoms. This should be done only under the guidance of a professional as it may not be suitable for everyone.

Seek support from a registered dietitian: Dietitians can help you avoid unnecessary restriction, protect your nutritional intake and interpret your symptoms.

For some specific conditions, validated tests do exist but these are not general “food intolerance” tests. Examples may include tests for coeliac disease, lactose intolerance and suspected food allergy.

When to seek medical advice

Speak to a GP if symptoms are persistent, severe or getting worse, particularly if you have unintentional weight loss, blood in your stools or black stools, persistent vomiting, difficulty swallowing, or a family history of coeliac disease or inflammatory bowel disease. These symptoms should not automatically be assumed to be due to food intolerance.

In conclusion…

If you are experiencing ongoing symptoms, it is understandable to want answers. However, commercial food intolerance tests are unlikely to give you a reliable one.

Instead, start by keeping a food and symptom diary, and speaking to a GP or registered dietitian. A structured approach can help identify whether food is playing a role, while avoiding unnecessary restriction.

If you ever experience swelling of the lips, tongue or throat, difficulty breathing, wheezing, or feel faint after eating, seek urgent medical help, as these may be signs of an allergic reaction.