Food Allergy, Intolerance and IgG Sensitivity Explained

If a food seems to disagree with you, you will hear three words used almost interchangeably: allergy, intolerance and sensitivity. They describe different things, they are tested in different ways, and mixing them up can lead to the wrong advice. This guide sets out what each term means and what a food sensitivity test can and cannot do.

Food allergy

A food allergy is a reaction by the immune system, and the type involved is called IgE (immunoglobulin E). When someone with an allergy eats the food, even a tiny amount, the immune system reacts quickly, usually within minutes to a couple of hours. Symptoms can include hives, swelling of the lips or face, vomiting, wheezing and, in serious cases, anaphylaxis, which is a medical emergency.

Common allergens include peanuts, tree nuts, eggs, milk, fish, shellfish, sesame and wheat. Allergy is diagnosed by a doctor or allergy specialist, who may use a skin prick test, a blood test for IgE antibodies or a supervised food challenge. If you think you have a food allergy, see your GP. Do not try to work it out with a home test, and do not reintroduce a suspected allergen on your own.

Coeliac disease

Coeliac disease is often lumped in with allergies, but it is a separate autoimmune condition triggered by gluten. It is diagnosed with a blood test and usually a biopsy, and you need to be eating gluten when you are tested. If you suspect coeliac disease, speak to your GP before you cut out wheat, barley or rye.

Food intolerance

Food intolerance does not involve IgE, and it is not usually dangerous. It tends to be about digestion. Lactose intolerance is the clearest example: some people make too little lactase, the enzyme that breaks down milk sugar, so the sugar ferments in the bowel and causes bloating, wind and loose stools. Reactions are often dose-dependent, so a splash of milk in tea may be fine while a large latte is not, and they can appear several hours after eating.

Other food intolerances come from reactions to chemicals in food, such as caffeine or histamine, or to certain fermentable carbohydrates. Diagnosis usually relies on keeping a food and symptom diary, an elimination diet supervised by a dietitian and, for lactose, sometimes a breath test.

Food sensitivity and IgG

“Food sensitivity” is used loosely, and it often means a delayed reaction that is not an allergy and not clearly an enzyme problem. Some tests for it measure IgG antibodies to foods. IgG is a different type of antibody from IgE. Your immune system makes IgG in response to many things it meets, including foods you eat regularly.

This is where the debate starts. Several allergy societies take the view that food-specific IgG mostly reflects exposure to a food, not a harmful reaction, and they do not recommend IgG testing to diagnose food intolerance. Others, including some practitioners and researchers, use IgG results as a starting point because they have found that people who remove high-reactivity foods sometimes report feeling better. The evidence is mixed, and large well-controlled trials are limited.

So the honest position is this. An IgG result is not a diagnosis of anything. It does not show that a food is harming you, and it does not rule out an allergy. At most it is one piece of information that can help structure an elimination diet.

How an IgG test can be used sensibly

If you choose to take an IgG test, a few ground rules help:

• Treat the result as a guide, not a verdict. A high reading on a food means “worth a closer look”, not “this food is bad for you”.
• Work with a practitioner, such as a nutritionist or dietitian, who can interpret the report alongside your symptoms and make sure your diet stays balanced.
• Remove foods for a set time, then reintroduce them one at a time and note what happens. The reintroduction is what tells you whether a food really matters for you.
• Do not use it to rule out allergy. Anyone with a history of swelling, wheezing or severe reactions should see their GP first.
• Avoid cutting out large food groups for long periods without advice, as this can lead to gaps in nutrition.

What our test measures

Our Food Sensitivity Advanced test uses a finger-prick blood sample you collect at home. The laboratory measures IgG antibody reactions to more than 270 foods and drinks and reports them on a simple scale. It also includes a total immune load measurement and an hs-CRP marker, which is a general marker of inflammation in the body.

It does not test for IgE allergy, and it does not test for coeliac disease or lactose intolerance. It is designed to give you and your practitioner a structured place to begin an elimination diet, particularly if you have symptoms that come and go and no clear trigger.

Next steps

If you have ongoing digestive symptoms, skin problems or fatigue and you suspect food plays a part, start by speaking to your GP, especially if symptoms are severe or getting worse. Once anything that needs medical attention has been ruled out, a food sensitivity test can be a practical next step.

You can find out more about Food Sensitivity Advanced or browse every kit in our shop. Many people also look at their gut bacteria alongside food reactions, and our GI Axis test covers that.