IgG food testing (also known as food sensitivity testing) was recently discussed in an editorial from Yale in the Annals of Allergy, Asthma and Immunology. The physicians at Yale sited the American Academy of Allergy and Immunology and the European Academy of Allergy and Clinical Immunology in recommending strongly against the use of IgG food testing.
IgG (Immunoglobulin G) is one of the main immune proteins in humans. It serves both “recognition” and “protection” functions. Homeland Security might serve as a reasonable metaphor. The latter has an extensive database of all individuals residing within and entering into the United States. It also can serve to protect from terrorists. Similarly, our immune system makes IgG antibodies of recognition against all substances that enter our bodies including the foods that we eat. Hence, we all have a myriad of IgG antibodies directed toward/recognizing these foods.
When a patient has IgG food testing done there is typically a long list of “positive foods” which are rated from mildly to strongly positive. Unfortunately, this list is used as a guide for food elimination to try and treat clinical symptoms.
Since food allergy (10% of the population) and food intolerances (20% of the population) are so common, it is often the luck of the draw with an avoidance of many foods that the patient will actually feel better.
But this clinical improvement comes at the cost of an often nutritionally poor diet and is due to the interdiction of one food (among many) that might actually be an allergen or an intolerance and not because the IgG antibody is causing the allergy or intolerance.
Allergy is caused by a different immune protein (IgE) Immunoglobulin E. And food intolerance is caused by digestive enzyme deficiencies or other physiologic issues with the gastro-intestinal tract.
Companies/laboratories that offer IgG food testing make claims that the test can help with a variety of medical problems including IBS (irritable bowel syndrome), joint pain, migraines, fatigue, and skin rash. IgG food testing and associated elimination diets can lead to an emotional burden and negative health consequences.
A too strict elimination of foods can cause nutritional deficiencies. Also, insurance companies usually do not
cover the cost of the tests (which are significant) because medical insurers recognize it as a non-standard process.
In 2004 the Mayo Clinic did a study in people with IBS. Half of the group had IgG food testing and were told to avoid the positive foods; the other half of the study group were placed on a sham diet not based on any testing. The clinical outcome was the same in both groups.