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Are IgG tests accurate indicators of food intolerance, specifically gluten and casein?
So, for those who don't know, IgG is the most important tailor-made antibody in the immune system's defense against invaders - including allergens. It remains long after the initial cause has been suppressed and attempts to prevent another “attack.” When someone is allergic to gluten, for instance, the body recognizes proteins from gluten to be foreign. The body then sends out antibodies, including IgG, to protect the body. With this said, IgG measures exposure to the potential allergen, not an allergy-related disease (such as Celiac Disease). Research is ongoing, but given the lack of correlation between the IgG and allergies, IgG testing is considered unproven as a diagnostic agent for allergies testing. Research shows that IgG is present in people who may or may not be allergic to gluten or casein (among other substances) but have been previously exposed. In the case of food allergies/intolerances/disease from allergens, IgG doesn't confirm even if elevated levels are observed. Also, keep in mind that allergies and intolerances are not the same as a food intolerance does not strike an immune response, which an allergy does.
For instance, when IgG antibodies are tested in gluten and casein allergies, a person is exposed to gluten who has an allergy may present with elevated levels which could indicate an allergy. However, in the absence of exposure, allergy or not, IgG levels can be normal despite the presence of an allergy. So, in this situation, it is not a confirmed diagnostic tool to assess whether someone has an allergy or not. Some research even suggests IgG can signify tolerance, not intolerance, to certain foods due to the ability for the immune system to build up antibodies to protect the body from the “foreigner.”
IgE, however, another antibody released in response to allergens, usually accompanies the responses to food allergies typically seen: flushing, itchy skin, wheezing, vomiting, throat swelling, and even anaphylaxis. Though this is not necessarily related to gluten or casein allergic reactions, IgE, rather than IgG, is the antibody usually correlated with an allergic response.
Food intolerances have been associated with symptoms such as Irritable Bowel Syndrome (IBS), bloating, tiredness, constipation, diarrhea, cramping, eczema, headaches and migraines. Consistent occurrence of these symptoms warrants talking to a physician and working with a registered dietitian to perform food elimination tests to truly confirm a food allergy. As for IgG testing, it is unclear whether IgG tests are useful at confirming a food allergy. If you experience symptoms that you think are related to a food allergy, seek help from a specialist/physician with the tools to accurately determine the root cause of your symptoms.
I hope this helps! Happy Eating!