All you have to do is search on Google «IgG food intolerance tests” either “IgG sensitivity test« to, among the almost half a million results, find all kinds of companies that are doing business with these tests. They are generally performed in clinical analysis laboratories, hospitals and private insurance companies, but also in some pharmacies.
Why are they not offered in public health? Simply because there is no scientific evidence that supports the relationship between the presence of IgG and these supposed “food sensitivities.” If the test were really reliable, dietitians and allergists would be happy to do them.
In search of IgG antibodies
When exposed to germs, the body produces specific antibodies designed to destroy only those germs. The immunoglobulin tests we refer to measure the amount in the blood of one of those defensive proteins: immunoglobulins G (IgG). Also known as IgG antibodies, they are produced by the immune system to combat attacks from viruses and bacteria, mainly.
IgGs bind to a variety of antigens, not only those of viruses and bacteria, but also toxins, parasites, and food proteins. In addition, the body maintains a “blueprint” of all the antibodies of this type that it has produced. That way, if you are exposed to the same germs again, the immune system can quickly produce more antibodies.
What do food sensitivity tests do?
The tests analyze a small blood sample with the aim of quantifying the presence of immunoglobulins G against various foods, generally between 100 and 200 simultaneously. Of course, the greater the number of foods included in the test, the higher the price, which usually ranges between 50 and 200 euros.
But the binding of IgG to food proteins does not imply an adverse reaction: it is simply a reflection of exposure to those foods.
In addition to overlooking that IgG antibodies only serve to fight infections, the business of this type of test is based on the ease with which “food intolerance” and “food intolerance” are often confused.food allergy«, two very different concepts.
How are allergies different from food intolerances?
The allergieswhich can be triggered by mite proteins, pollen, animal hair or food, are an immediate and severe direct response of the immune system that revolves around a protein called IgE, short for immunoglobulin E.
IgE is an antibody that triggers a sudden allergic reaction like the one suffered by, for example, someone with peanut allergy who eats that legume and, among other symptoms, feels a blockage in his throat.
On the other hand, food intolerances are related to the difficulty of digesting certain foods. They have nothing to do with the immune responses triggered by immunoglobulins that characterize allergies.
In allergic episodes, the B lymphocytes of the immune system interpret the harmless proteins present in certain foods as harmful. This misinterpretation causes a normally harmless substance, such as a peanut, to be taken for a threat against which a defensive immune response is launched that can be dangerous and potentially fatal.
In short, the immunoglobulins that are triggered in allergies of any origin are exclusively IgE, which have nothing to do with other immunoglobulins involved in microbial infections. Therefore, in tests to diagnose allergies – including food allergies – what doctors look for are IgE levels against the element that could be the responsible agent.
At a molecular level, what happens is simple: a protein present in peanuts binds to that Y-shaped IgE antibody that protrudes from the surface of a mast cell, a specialized type of white blood cell. This contact causes the mast cell to release histamine and other inflammatory molecules.
The results of that process are redness, swelling, and, in some extreme cases, death. By the way, this is the same principle that applies when an allergist pricks a patient’s skin to find out what they are allergic to. The needles are coated with the protein of a particular element that can cause allergies, and the protein will bind (or not) to IgE on the surface of that person’s mast cells.
Intolerance has nothing to do with the immune system
IgG food intolerance tests pit a blood sample against a panel of foods and food components. Then, using a technique known as an immunosorbent assay, the degree to which IgG in the blood binds to each element is quantified.
Although immunoglobulins are used in these tests, intolerances do not cause an immunological reaction. Intolerances are difficulties digesting or metabolizing certain foods, as is the case with the most widespread of them: lactose intolerance.
In this case, the intestine produces little or no lactase, the “molecular scissors” that cut lactose into glucose and galactose. Undigested lactose reaches the colon, where bacteria ferment it, generating gas and causing bloating. Unlike an allergy, which activates the immune system, intolerances do not.
The laboratories that market these tests want us to believe that IgG is somehow involved in this intolerance and that, in the same way that IgE prick tests work for allergies, the more binding there is between IgG and the food, the more pronounced the intolerance will be.
It’s not like that. Determining food intolerances requires a more comprehensive approach: patient history, physical examination, and a short-term elimination diet followed by another supervised by a qualified nutritionist.
This article was originally published in The Conversation.
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