Testing for Food Sensitivities: Is IgG the Answer?
We’ve all been there. After trying something new at the company potluck you’re struck with a barrage of unpleasant symptoms including gas, bloating, stomach pain or diarrhea. What could have caused it? Was it the kale salad your cubicle partner brought that was forced upon you when you were cornered? Or maybe it was the egg salad sandwiches that you thought you saw moving out of the corner of your eye? Either way, in the back of your mind, you now suspect that you have a food sensitivity to something you put in your belly.
First of all, what is a food sensitivity? The American Academy of Allergy, Asthma and Immunology (AAAAI) describes food sensitivities as an intolerance to a food where the body does not process the food properly. They do not consider food sensitivities to be dangerous and note that food sensitivities are actually different than food allergies, which are dangerous immune reactions to food. The most well-known food sensitivity is lactose intolerance, a condition where the body does not produce enzymes required to breakdown the sugar in dairy products. So how do you know if you have a food sensitivity?
Unfortunately, the answer to which foods you are sensitive to is not a simple one. According to the AAAAI no one test can confirm whether or not a person has a food allergy, partly due to the fact that we’re not entirely sure what causes food sensitivities at this time. In fact the term “food sensitivity” is an umbrella term that may describe many different food processing abnormalities that each have different causes. The aforementioned lactose intolerance is caused by the missing of a key enzyme but other sensitivities may have anatomical/physiological causes specific to that individual, or may even have low-levels of immune system involvement that are distinct from traditional allergy responses. This is still an area of active research and because of its diversity of hypotheses there is no one-size-fits-all test.
So now for the question at hand: what about IgG tests and are they accurate in testing for food sensitivities?
IgG is an antibody, a substance produced by the immune system. There are many different types of antibodies but IgG is by far the most common in the human body and functions primarily to fight off infections, but also plays a role in allergic reactions.
The logic behind using IgG as a marker for food sensitivities comes from studies that have noted increases in levels of IgG as a response to ingesting certain foods in different people. As an added bonus IgG tests are conveniently available to patients at home, requiring no more than a drop of blood from a finger to be able to detect dozens of IgG-food reactions.
Sounds great right? The problem is that the AAAAI does not recommend IgG testing at all for determining which foods a person may have sensitivities to. From the AAAAI:
“It is important to understand that this [IgG]test has never been scientifically proven to be able to accomplish what it reports to do. The scientific studies that are provided to support the use of this test are often out of date, in non-reputable journals and many have not even used the IgG test in question. The presence of IgG is likely a normal response of the immune system to exposure to food.”
They go on to state that IgG levels may even be a sign of the body’s tolerance to food, as opposed to intolerance!
So what can a person do if they think they may have a sensitivity to a food but want definitive proof? Some strategies that exist involve refraining from certain food groups for short periods of time and reintroducing them one by one back into the diet to see which ones cause a reaction. These diet changes can be somewhat involved and the AAAAI recommends consulting an allergist/rheumatologist in order to come up with a plan to diagnose your specific sensitivities.
Thanks for reading,
Stephen Wang
2020 PharmD Candidate
