IgG is one of many immunoglobulins, i.e. antibodies, that are formed when you eat a certain food. Manufacturers and suppliers such as Kiweno say that a gut damaged by our lifestyle makes it permeable and our immune system reacts to food components that pass through the gut illegally, so to speak. This would be called a type III allergy to food (1,2). This then leads to inflammation and other problems. If you were to avoid the foods to which you are allergic according to the test for at least eight weeks (1), you would soon feel better. Sounds logical.
My gluten experiment
I love bread and everything that contains gluten. I also eat a lot of it and tolerate it very well. But to make the self-test a little more meaningful, I ate almost only seitan products (seitan is pure gluten) and bread for two days before the test. Seitan dumplings, seitan schnitzel, lots of bread and also a very tasty cake. I suspect that the IgG value of my measurement will be high and that I will be diagnosed with a gluten intolerance through this test, so to speak. I do the same with herring. But more on this in one of the next blogs. However, my IgE value for cereals should be low, as I am not allergic. I cannot say in advance what the stool test will reveal. I’ll be surprised.
By the way, I feel great after the gluten bombs. I have no symptoms either immediately afterwards or days later.
The results of the gluten tests
My allergy test at the University Hospital in Innsbruck showed that I am not allergic to wheat or other cereals. I also don’t have coeliac disease or any other gluten-related illnesses. As already mentioned, I don’t have any symptoms either.
Let’s say, as a thought experiment, but I would have symptoms. Then I would google and inevitably come across self-tests for home use. Whether stool test (e.g. medivere) or blood test (e.g. cerascreen, Kiweno, Yorktest, …). So I would order these tests, do them and then wait for my results. In my case, I do a gluten stool test, an IgE test and the IgG blood test also covers gluten and all possible grains.
After a few days I got the result: the stool test said everything was fine, I tolerated gluten perfectly. The IgE test does not find an allergy to wheat or rye flour – just like the IgE test I had done in hospital. The IgG test, on the other hand, says I have “ leaky gut syndrome ” and would react very strongly to gluten and cereals. I should strictly avoid all cereal products for three months. Aha… Well, two tests are right, one is wrong. I go to a laboratory doctor with the results and want to know what she thinks of these tests.
What do experts say about my test results?
So I visit Prof. Dr. Griesmacher, head of the central laboratory at Innsbruck University Hospital, and show her my findings. She is amazed that such tests exist. You are particularly surprised by the stool test, as these stool tests for gluten were probably carried out many years ago and were classified as useless in laboratory medicine. That is why they have not been used in medical practice for a long time, she says. She would not rely on the result.
I explain to the professor that the IgG test might be due to the fact that I had eaten a lot of seitan. She is not sure whether it works that way, but explains to me what I had already found out in my research, namely that these tests are not considered meaningful by international specialist organizations. If I don’t think I can tolerate gluten, I should see a gastroenterologist, she says. If only because I have to have the findings explained to me. Ok. I’ve heard that before too… And of course I go to a gastroenterologist.
Stool test for gluten is useless
Dr. Straub, an expert on coeliac disease and also employed at Innsbruck University Hospital, explains to me that the results of the stool test are useless for screening for coeliac disease. These tests are not accepted as screening tests because the sensitivity is far too low. These tests would also not be sufficiently reliable for diagnosing positive results. And indeed, studies have extensively tested celiac disease patients and healthy people with such tests. With the stool test for transglutaminase antibodies, only 10% of patients with coeliac disease were identified as having the disease, while 50% of patients with a positive test result were proven to be healthy (3). That really is a very poor hit rate.
Let’s stick with our mind game and say I had symptoms, googled and did these three tests. What would I know now?
Nothing… I would be just as smart as before. From a purely psychological point of view, however, I would probably believe the IgG test, because I have symptoms and am desperately looking for a reason. I would now avoid wheat products and gluten for three months.
What IgG tests really do
I speak with Univ.-Doz. Dr. med. Kofler one of the leading allergy specialists in Austria. He confirms what all the leading allergy societies tell me. IgG tests only show the extent of contact with the food, they are an “expensive food diary”, so to speak. So-called type III allergies to food – often called food intolerance by test manufacturers – do not exist (4). If I eat a lot of bananas, my IgG value for bananas rises; if I hardly eat any apples, my IgG value for apples is low. It can therefore be assumed that the IgG tests only show what kind of eating habits you have. This is why the European allergy societies even expressly warn against the “misleading laboratory tests”. “Determinations of IgG antibodies against food are clearly to be rejected and should no longer be recommended” (5). The Austrian Association of Dietitians recently posted this warning on Facebook.
Dr. Kofler also explains to me that IgG levels only rise six to eight weeks after contact with the food. My seitan provocation a few days before the blood test was therefore not the decisive factor for this measurement. Too bad. But I still have my herring provocation up my sleeve…
How to test food allergies professionally
Allergies to food can only be clearly identified, Dr. Kofler explains to me, with a detailed patient consultation, IgE tests, a symptom diary, skin tests – so-called PRICK tests – and optionally with a provocation and omission diet. An IgE test alone, as I did it as a home test, works in principle, but is not effective as it does not say much on its own. There are many sensitizations that are not clinically relevant but can give misleading results in such a test. He showed me from my results: according to my IgE results, I also reacted to wasp venom, so I should be allergic. I have a small vegetable garden in the countryside and get stung by wasps 1-2 times a year. However, my reaction to it is not much stronger than to a mosquito bite. This result is therefore not clinically relevant. Therefore, an IgE test must always be carried out together with the other test methods in order to obtain clear results, explains Dr. Kofler. An evaluation of the test by a doctor is therefore absolutely necessary.
Food intolerances, i.e. fructose or lactose intolerance, can only be diagnosed with a diary, medical history and H2 breath test. The diagnosis of coeliac disease is complex and cannot be made with just any home test. Leaky gut syndrome”, i.e. the intestinal permeability propagated by the manufacturers, does indeed exist, but not in the form propagated by the suppliers and certainly not measurable via the laboratory values obtained in the tests. “Leaky gut” is an interesting topic, but we will leave it out for the sake of simplicity. Perhaps a separate blog entry will follow soon…
IgG tests are “addictive”
Well, back to our thought experiment. So after the IgG test, I would restrict myself, pay more for gluten-free products and chastise myself for eight weeks to six months. And then? Perhaps I would then do another IgG test. This is what most manufacturers recommend. And then maybe the IgG test would say that I can now tolerate it again. Yay! So over 200 euros and three months later, I’m tolerating what I’ve always tolerated. Or he would say, no, you’re still reacting. Then I would just continue not to eat gluten. Although I would tolerate it perfectly.
Someone always wins: the manufacturer
From the manufacturer’s point of view, this is great, because ideally you don’t just buy these tests once, but again and again at intervals of several months. And it’s even better to test the whole family. That’s why there are usually also offers for family packs. That pays off. For the provider. In a start-up show, I learn that one such IgG test provider sells around a thousand per month. At a cost of usually over 100 euros per test, this is a million-dollar business that is very popular with investors.
Scientific studies for or against IgG tests?
But why do these tests still exist when the scientific situation is clear? A manufacturer of such tests recently posted studies in a blog that are supposed to prove that IgG tests work and bring about an improvement. I’m looking at these four studies, because maybe the professional organizations are wrong? Perhaps IgG tests are useful after all?
The first study cited comes from a manufacturer of such tests itself and is therefore not objective. Two other studies relate to irritable bowel syndrome patients, not “normal people”, and the fourth study was published in a naturopathic journal. However, there is no control group, which of course makes the study useless. So I take a closer look at the two irritable bowel syndrome studies. The first is also not a placebo-controlled double-blind study and is therefore not considered scientific (6). The second is, drum roll, double-blind and placebo controlled (7). Irritable bowel patients were tested and then two groups were created. One group was switched according to the IgG result (real group), the other was given a sham diet where only foods were omitted to which the IgG test found no “allergy”. And lo and behold, some of the real group felt better after the diet, while most of the sham group did not. The study sees this as proof that IgG tests work.
Irritable bowel syndrome patients are not “normal”
Sounds logical. But if we think about what the IgG value means, then we remember that IgG only indicates what I eat a lot of and what I eat a little of. Even the IgG advocates do not doubt this. If I am an irritable bowel syndrome patient with symptoms, it means that I am eating something that I cannot tolerate. If I now leave out what I eat a lot of, there’s a good chance that it’s what I can’t tolerate. And that’s exactly what the IgG test shows, it shows what I eat a lot of. It is therefore true that the IgG test can help irritable bowel syndrome patients. Even if they could have simply followed a FODMAP diet or kept a symptom diary instead… Incidentally, this study is highly controversial among experts, also because of other problems such as the number of test subjects or data interpretation (8).
However, this only applies – as has been known for some time – to irritable bowel syndrome patients and with the note that it has nothing to do with allergies or the mechanism described by the manufacturers, but quite simply with carbohydrates contained in the food, which influence the intestinal flora. Unfortunately, this does not apply to “normal people”.
In the end, none of the studies mentioned by the manufacturers show what the manufacturers would like. But that doesn’t seem to matter to the normal customer. As soon as a study is posted somewhere and it is claimed that it proves XY, the consumer seems to believe it.
My gluten test: the conclusion
Back to our example: If I had symptoms, what would I have to do now after my tests? Well, I should probably go to the doctor and have a diagnosis made, including a coeliac diagnosis. And I should tell him about my self-experiments, because a gluten-free diet before the diagnosis of coeliac disease would falsify the result. Only then, after my visit to the doctor, would I have certainty. And if I had done this right away, I would have saved myself 3 months of abstinence and over 200 euros for tests that make no statement about gluten tolerance…
1st laboratory practice Jochen Hüter. InVita Lab [Internet]. Available from: http://invitalab.de/informationen/allergie-diagnostik/allergie-typ-3/
2 Kiweno GmbH. Kiweno [Internet]. Available from: https://kiweno.com/faq/sind-nahrungsmittelunvertraeglichkeiten-eine-form-von-allergie/
3 Kappler M, Krauss-Etschmann S, Diehl V, Zeilhofer H, Koletzko S. Detection of secretory IgA antibodies against gliadin and human tissue transglutaminase in stool to screen for coeliac disease in children: validation study. BMJ. 2006;332(7535):213–4.
4 Ledochowski M, editor. Clinical nutritional medicine. Springer Vienna New York; 2010.
5. ÄDA, DGAKI, GPA, ÖGAI, SGAI. No recommendation for IgG antibody tests against food. Press release. 2009;
6 Clarke DP, Burdette C, Agolli G, Dorval B, Gaston A, Chesla S. The Relevance of Using the C3d/Immunoglobulin G Test in Clinical Intervention. Altern Ther Health Med. 2015;21:16.