Food Intolerance Test in Malta: Do IgG Tests Work? A Doctor's Review

Many people live with bloating, abdominal pain, unpredictable bowels, low energy or migraines. Often they have tried cutting out the foods they react to, and their tests keep coming back normal. But they intuitively feel there is a connection between their food and their symptoms, one they might not be able to fully see.

Eventually, they start thinking about whether a food intolerance test is a good idea. They see that there is a lot of controversy surrounding testing for food sensitivity. And almost everything they come across seems to come from two camps: the institutions, and the companies selling the test.

So most people are left to decide on their own.

This is my honest review as an integrative doctor: the reasons why most of my medical colleagues and institutions typically say no, and the reasons why some healthcare practitioners, including myself, sometimes say yes.

I never learnt a lot of what I write here in medical school or postgraduate exams, so I can understand why many doctors and specialists might disagree with some of what is written here. But I hope the reader can read the following with an open mind and curiosity.

What is a food intolerance test?

A food intolerance test measures the level of IgG antibodies in your blood against a panel of foods. Some tests measure more foods than others, and the reports are typically quite straightforward to read.

An IgG stands for Immunoglobulin G. An immunoglobulin is a protein made by your immune system as part of its natural defence mechanism. There are many types of immunoglobulins. The two most important for this discussion are IgE and IgG.

IgG reactivity is based on exposure. If you have already cut out the foods you suspect, your reactivity to them may come back lower than expected. This is one reason a dietary history, and working with a health professional after the test, can be helpful.

However, to understand whether this test can be useful, I think it is first important to understand the difference between a food allergy, a food intolerance and a food sensitivity.

What is a food allergy, and how is it diagnosed?

A food allergy is a rapid immune reaction to a food protein: the body produces IgE antibodies that mistakenly treat it as dangerous. Reactions occur within minutes and can be life-threatening, with symptoms such as hives, swelling of the lips, face, eyes or tongue, trouble breathing and dizziness. In an acute reaction, call 112 or go to the emergency department immediately.

Diagnosis typically starts with your history, then a skin prick or IgE blood test, sometimes followed by a supervised food challenge with an allergy or immunology specialist, who also advises which foods to avoid and how to manage reactions.^{1, 2}

What is the difference between food intolerance and food sensitivity?

Officially, all reactions to food sit under one umbrella term, “food hypersensitivity”. If the immune system drives the reaction, it is a food allergy. If it does not, it is a food intolerance.^2–4

This is where I think the confusion starts.

Most labs sell their IgG test as a food intolerance test. But IgG is made by the immune system. So the test measures your immune system, under a name that officially means your immune system is not involved.

But your body rarely stays inside these boxes. The immune system is in constant conversation with the mind, the hormones, the nerves, the blood vessels and even the platelets, the tiny cells that help your blood clot.^5–9

So in this article I use the following definitions found in some scientific papers. They keep the name you will see on your test report, and they separate reactions by what may be driving them.

• Food allergy: an immune reaction through IgE, which is immediate and can be life-threatening.^{2, 3}
• Food intolerance: a delayed immune reaction to a food, hours or days after eating it, where IgG to the food is raised.^10–15
• Food sensitivity: everything else, for example FODMAPs, or a drug-like effect, such as with histamine or salicylates.^{4, 16, 17}

What guidelines call food intolerance is closest to what I call food sensitivity here.

Many specialists would disagree that IgG drives any of these reactions, and I set out their reasons below.

Are food intolerance tests accurate? Why most doctors say no

Gastroenterology and allergy associations worldwide advise against IgG-based food testing for IBS and food allergy, as do a number of very well-known institutions, including the NHS and the Mayo Clinic.^{1, 18–22} This is why most doctors and specialists do not order this test.

Their argument is that higher IgG antibodies to a food are a normal response to eating it: it shows you have eaten the food, not that the food is harming you.^{1, 18–20} That is why people with no symptoms test positive,^{18, 23} and why the highest results are often the foods you eat most.^{18, 24, 25} So if people feel better on an IgG-guided diet, it may simply be from cutting out common triggers such as wheat and milk.^{26, 27} The tests themselves are unstandardised, and the studies in their favour, they argue, are too old or too limited, which leaves the tests unproven.^{1, 18–20, 28–30} And even if all of that were set aside, they argue that these tests can lead people to cut out food groups needlessly,³¹ and make them anxious about food.

Do food intolerance tests work? What the trials show

Some trials suggest it can help. People who follow an IgG-guided elimination diet report fewer symptoms across migraine,^{15, 32–36} IBS,^{31, 33, 34, 37–43} Crohn’s disease,^44–47 ulcerative colitis,⁴⁸ chronic pain,⁴⁹ eosinophilic oesophagitis,⁵⁰ skin and breathing symptoms in children,⁵¹ acne⁵² and poor sleep.^{15, 53} Some of the strongest trials compared two groups: one removed the foods their IgG test flagged, the other removed the same number of foods the test said were fine. In five of six, the IgG group did better.^{29, 35, 37, 38, 44, 45}

But if these trials are showing improvements, could there be a mechanism that explains it?

What might cause food intolerance?

These are some important considerations from my perspective.

1. The gut barrier

Normally, your gut breaks food proteins down into tiny pieces, and its lining lets very few whole proteins through. When the lining is inflamed, more of them can slip across.^54–57 Your immune system notices, and responds as it is designed to: by making IgG antibodies against them.^{58, 59} That response is what an IgG test measures. In some people it may cause nothing at all. In others, it may be linked to inflammation elsewhere in the body, the brain included.^{15, 60–63} Modern life, from detergents and some food additives to air pollution, may be further damaging the thin linings of our gut, skin and lungs, and may help explain why allergies and autoimmune conditions have risen so quickly.⁶⁴

2. The body adapts to a food, then struggles

From the 1950s onwards, the allergist Theron Randolph described what he called specific adaptation.^{65, 66} Initially the body is not yet adapted to a food it is intolerant to, causing mild symptoms. Then the body gets addicted to the food as it adapts, then it becomes maladapted which is where symptoms start becoming more prominent and the patient starts seeking help, and finally exhausted where the body can no longer adapt. This is how he explained why elimination and reintroduction one at a time can help find the cause.^{30, 67–74} Whilst this is contested,^{75, 76} it does fit in with concepts used in other aspects of holistic healing, such as Hans Selye’s model of stress.⁷⁷

3. The mind and the immune system

In the example above, the stressor was food. But as Hans Selye described, the same pattern can apply to psychological stress. This may help explain why psychological distress is thought to be one way the gut loses tolerance to a food it previously handled well,^77–79 potentially by making the gut lining more permeable.⁸⁰

What also makes sense here is that the immune system can learn by association. If a smell is paired with an allergic reaction often enough, the smell alone can eventually trigger histamine release.⁸¹ The same learning can also dampen allergic reactions.^82–84 Similarly, people who expect a food to upset them can react to a placebo just as strongly as to the food itself.⁸⁵

In my clinical experience, this is where some patients’ stories begin: a food eaten, or a smell present, during a difficult period or a big life transition, and a reaction that returns every time since.

Should you have a food intolerance test? How I decide

After taking all of the above into account: do I think the potential benefits of doing this test outweigh the risks? From my perspective, yes. And I fully understand that I am going against the consensus and the norm in conventional medicine here. I am more than happy to debate that with specialists and other professionals, and I will change my mind if there is something I am missing.

However, an IgG test followed by an elimination diet is very rarely the full plan. There are usually far more factors to take into consideration. For example, if you test positive on this test, is this likely to be a healthy response or not? Is there a likelihood of nutritional deficiencies, secondary anxiety or practical issues in following through? Can this be explained from your dietary history or not? Is an alternative diagnosis more likely from a conventional perspective such as SIBO, coeliac disease or lactose intolerance? What is happening here from a Chinese Medicine and Ayurvedic perspective? My full method is here.

What would change my mind

Two things would change my mind. First, if someone can show how the risks outweigh the benefits, taking into account the trials above where people improved on IgG-guided elimination diets. Second, if a patient’s diet, from my assessment, is not strongly contributing to their current issues, or if I believe there is a much more effective way to get a strong result, then I would not order this test.