by Ryan Whitcomb, MS, RD, CLT
As a dietitian who specializes in food sensitivities, I’m often asked about immunoglobulin G (IgG) testing as a 
method for uncovering hidden food sensitivities in the diet. This comes as no surprise to me because various companies heavily market this method of testing as a quick, easy and accurate way of diagnosing food-induced sensitivities. The concept behind the test is simple: High levels of IgG to a food are indicative of a sensitivity and low levels are not.
However, this premise is false. Really false. In fact, high levels of IgG only indicate that the individual has been repeatedly exposed to the food, but it does not tell us if that exposure was tolerated by the immune system (harmless) or caused an inflammatory reaction (harmful). This is a huge limitation of the test. For anyone that has ever received a positive IgG result without corresponding symptoms to that food, this is why. It might just mean your immune system tolerates that food and is not reacting to it.
Food sensitivities are categorized into two classes: type III and type IV reactions (allergies are type I). Type III reactions involve IgM, IgG and complement, whereas type IV reactions involve T cells. This is an important distinction because even if we assume that high levels of IgG indicate a sensitivity (which it does not), IgG testing ignores the other players of a type III reaction, IgM and complement, and it ignores type IV reactions completely!
Can you see how this is a big problem?
Though all tests have limitations, when testing for food sensitivities, it’s important to use a test that detects all mediators, regardless of which type of reaction is occurring. It is for this reason that I do not recommend IgG testing.
Source: Ryan Whitcomb, MS, RD, CLT, owner of GUT RXN Nutrition, a private practice where he treats individuals with digestive disorders and chronic inflammation related to food sensitivities. For more information, call 866-321-2035 or visit Gutrxn.com.
