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Tests & procedures · UK

Food intolerance tests: what the evidence says

Why IgG food intolerance tests are not diagnostic, what the science actually supports, and how genuine intolerances are identified.

Key points

  • Most commercial intolerance tests measure IgG antibodies to dozens of foods; validated alternatives include hydrogen breath tests for lactose malabsorption and coeliac serology for gluten-related disease.

  • Breath tests require fasting and a low-fermentation diet the day before; IgG panels need no preparation, which reflects how little they measure.

  • Commercial IgG results typically arrive within 1 to 2 weeks; breath tests are interpreted the same day or within days.

  • Any result should be discussed with a doctor or registered dietitian before cutting foods, since unsupervised exclusion diets carry nutritional risk.

  • Allergy bodies including the British Society for Allergy and Clinical Immunology advise against IgG food testing: IgG antibodies indicate exposure and tolerance to a food, not intolerance.

About this test

Published 2026-09-27 · Next review 2027-09-27

This is a page where honesty matters more than a sale: IgG food intolerance tests, despite their popularity, are not supported by evidence and routinely flag long lists of foods the person tolerates perfectly well. Genuine food intolerance is real, but it is identified through validated routes: breath testing for lactose, coeliac testing before removing gluten, and a structured, time-limited elimination and reintroduction diet supervised by a dietitian.

A private GP, allergist or registered dietitian can arrange the validated tests and supervise an elimination protocol, which outperforms any mail-order antibody panel. Waiting lists for NHS outpatient assessment remain long in much of the UK, and many of these checks are not offered on the NHS at all unless you meet strict criteria. Private clinics can usually see you within days on a self-pay basis, with no GP referral needed in most cases.

Frequently asked

Common questions about Food intolerance tests: what the evidence says.

Quick, plain-English answers to what people ask us most.

  • What do food intolerance tests claim to measure?

    Many commercial food intolerance tests measure IgG antibodies to various foods, on the theory that raised IgG levels indicate foods your body reacts badly to. This is different from true food allergy, which involves the IgE antibody and immediate reactions.

  • Why do people take these tests?

    People often try them hoping to explain symptoms like bloating, fatigue, headaches, or skin issues by identifying foods to eliminate. The appeal is a seemingly personalised, actionable result rather than trial-and-error elimination.

  • What does the evidence actually say?

    Major allergy and immunology bodies, including the UK's Royal College of Pathologists and international allergy societies, do not recommend IgG food testing for diagnosing intolerance. Having IgG antibodies to a food is common in healthy people who tolerate that food perfectly well, so a raised result doesn't reliably indicate a problem.

  • Is there any preparation needed?

    If you do choose to have one of these tests, no special preparation is usually required, though results should be interpreted cautiously given the limited evidence base.

  • What happens during testing?

    Testing is usually a simple blood sample, sometimes a finger-prick sample sent by post, which is then analysed for antibody levels against a panel of common foods.

  • Are there risks to acting on the results?

    The main risk isn't the test itself but unnecessarily restrictive diets based on inconclusive results, which can affect nutrition and quality of life without addressing the real cause of symptoms. This is why any elimination should ideally be guided by a dietitian or doctor.

  • What should I do if I get an abnormal result?

    Rather than eliminating foods based on the result alone, it's best to discuss findings with a doctor or registered dietitian, who can consider your symptoms in context and suggest properly evidenced approaches, such as a supervised elimination and reintroduction diet.

  • How much do these tests cost, and are they available on the NHS?

    IgG food intolerance tests are not offered on the NHS because of the limited evidence supporting them, and they are usually only available privately, with cost varying by provider. NHS-recognised allergy testing for suspected true allergy is available through GP referral where clinically indicated.

  • Are food intolerance tests accurate?

    Independent reviews have found IgG testing does not reliably distinguish people with symptoms from those without, and results can vary between laboratories. For this reason, it's best viewed as having limited diagnostic value rather than a definitive answer.

  • What's a better alternative if I suspect a food problem?

    A structured, supervised elimination diet with reintroduction, guided by a doctor or dietitian, along with proper allergy testing if allergy is suspected, is generally considered more reliable. You can book a consultation with us to discuss symptoms and appropriate next steps.