Do home food intolerance tests work?

No. The NHS does not recommend food intolerance tests you can buy: there is limited evidence they give accurate results, and they may suggest avoiding several foods, which can be harmful. None of the common types, from IgG blood tests to hair analysis, has good evidence behind it. A dated food diary and a supervised exclusion find triggers.

That warning about cutting out several foods at once is the part worth sitting with, and it comes up again below.

Is a food intolerance the same as a food allergy?

No, and mixing them up is why the testing question gets so confusing. The NHS describes a food intolerance as “when you have difficulty digesting certain foods or ingredients in food”, which is different to a food allergy, “which causes symptoms such as itchy skin, wheezing, or swelling of the lips, face and eyes”.

An allergy involves the immune system, can be identified with established tests, and can be serious. An intolerance works differently, and there is no blood test that reliably names the food. Most tests sold online are sold for the one that has no test.

What do home intolerance tests claim, and what does the evidence say?

Each claims to find your trigger foods. The evidence column below is quoted from the British Dietetic Association’s review of these tests, which concludes that “alternative allergy testing should be avoided as it has no scientific basis”.

Why does an IgG test come back positive for so many foods?

Because IgG doesn’t measure what the marketing says it measures. IgG antibodies to food turn up in all healthy people without food allergies, so a raised IgG to bread, milk and eggs in someone who eats bread, milk and eggs is not a surprising finding. Guts UK’s verdict is that there is “no evidence that these tests can successfully identify a food intolerance”, and for IgG in particular “no strong evidence that these tests accurately identify a food intolerance”.

The real cost is the list. Cutting out a long run of foods can be challenging and may increase the risk of nutritional deficiencies, especially without support from a qualified healthcare professional. If bloating is what sent you looking, the dietitian led route is in low FODMAP on the NHS. If you were weighing up a breath test kit instead, read should I get a SIBO test.

What has the UK advertising regulator ruled about intolerance tests?

That the claims don’t hold up when it asks for the evidence. The Advertising Standards Authority’s guidance on allergy and intolerance testing collects a run of rulings.

On IgG testing, a 2021 ruling found “the evidence overall was not sufficiently robust to demonstrate that the elimination diet based on the IgG testing alone could be used to diagnose specific food intolerances”, and a 2025 ruling found claims based on IgG testing misleading.

On vega testing, the guidance notes that “several published double-blind studies have concluded that the test was not capable of diagnosing respiratory allergy”, and a 2011 ruling found the evidence “was not sufficiently robust to substantiate claims that this method of testing could be used to identify intolerance”.

On hair analysis, a 2013 ruling went against unsubstantiated claims that it could test for a large range of food intolerances. In April 2026 the regulator upheld a complaint about a hair sample test advertised as covering 1,500 food and non food items, found the advertiser had not provided evidence to substantiate the claims, and ruled the advert misleading.

A ruling against one company is not a verdict on every company. But the claims keep failing when a regulator asks for the evidence.

Which tests does the NHS use for food problems?

Real ones, for specific conditions. For suspected food allergy, the NHS lists “a skin-prick test (where a drop of liquid containing a food you may be allergic to is put on your skin to see if it reacts)”, blood tests, and “a special diet where you avoid eating the food you might be allergic to, to see if your symptoms get better”.

For suspected food intolerance, you may be referred to a dietitian, and the options include a supervised diet avoiding the suspected food, blood tests, and breath tests for lactose intolerance.

For coeliac disease, which is an autoimmune condition rather than an intolerance, your GP can take a blood test to check for antibodies. Coeliac UK recommends including at least 3g but preferably 6g of gluten every day for at least six weeks before testing, and says “it’s essential to continue eating gluten until your doctor makes a diagnosis”, because stopping is “very likely to cause an inaccurate result for both the blood test and the gut biopsy”.

That is the strongest argument against cutting foods out because of a bought test. Do it in the wrong order and you can make the real test unreadable.

What identifies a food trigger?

A dated food and symptom diary, then a supervised exclusion and reintroduction. If you are referred, you may well be asked to keep that diary anyway. Guts UK describes the method plainly: “the gold standard method of identifying a food intolerance is to exclude the food item. Symptoms should go when removing the food, and more importantly, reintroduce the food and symptoms should return.” No test is needed for it, and a dietitian should advise you throughout.

The reintroduction is the step people skip, and it is the one that does the work. Symptoms can ease after you remove a food for several reasons. Symptoms coming back when you put it back is much harder to explain away.

A diary is only useful if it is specific: dates and times, what you ate rather than the name of the dish, the symptom and how bad it was, and what else was going on that day, including sleep, stress, shifts and your cycle. The Seven Day Bloating Log is a week of that, built to take to an appointment rather than to use on its own. It identifies nothing by itself; the point is that you and a clinician read real dated entries. What to tell your GP about gut symptoms covers how to bring it up, and the bloating quiz can help you decide whether a log is the right next step.

When should I see a GP instead of keeping a food diary?

When a diary is the wrong tool. The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you are “losing weight without trying to”, if you “bleed from your bottom”, if you have “problems with swallowing food”, or if you have “bloating that does not go away or keeps coming back”. If any of those apply, contact your GP or NHS 111 rather than starting a diary and waiting to see what it shows.