Suspect a food allergy or sensitivity? Take these steps to find out

If you are dealing with symptoms such as hives or bloating, you may suspect a food allergy or sensitivity. But how can you determine which foods are causing the reactions? There are so many food allergy and sensitivity tests available, it can be difficult to figure out where to start. But with the right methods and doctor involved, you can often zero in on the problem.

If you search online for "food allergy testing," you'll find options including clinical visits with allergists and immunologists and do-it-yourself test kits that claim to deliver comprehensive results (with a 100 percent money-back guarantee!). Not all of the methods are equally reliable, and some are downright fraudulent. There is no single test that will tell you exactly which foods to avoid. If a website, advertisement or practitioner claims to provide such a test, watch out. Take these steps instead.

Allergy or sensitivity?

It's important to know the difference between a food allergy and a food sensitivity. Although the terms are often used interchangeably and symptoms may overlap, they are not the same. A food allergy is an immune system reaction that can cause hives, wheezing, itching, diarrhea, vomiting, shortness of breath and anaphylaxis. About 3.6 percent of Americans have food allergies, according to a 2017 Brigham and Women's Hospital study.

Food sensitivity (sometimes called food intolerance) is a reaction that involves the digestive system, not the immune system. Symptoms include gas, bloating, nausea, vomiting and diarrhea. Although intolerances can be painful and uncomfortable, they are not life-threatening, and are rarely as serious as true food allergies. Anywhere from 2 to 20 percent of Americans may be sensitive to certain foods - there are no precise numbers because there is no exact diagnostic test.

For food allergy

If you suspect a food allergy, don't self-diagnose or use at-home test kits. Food allergies are much too serious to assess without an expert. Your best bet is to work with a board-certified allergist, who will perform skin-prick tests and IgE blood tests to narrow down a diagnosis. (IgE, or immunoglobulin E, is a type of antibody produced by the immune system. More IgE is produced during an allergic reaction.) But keep in mind that even these tests are imperfect, and may falsely show you are allergic to something.

"Both skin and blood IgE tests have high rates of false positive results and, because of this, they should never be used as 'screening tests,' " says David Stukus, an allergist and associate professor in the division of Allergy and Immunology at Nationwide Children's Hospital in Ohio. "Both skin-prick and blood test results must be interpreted in the proper clinical context and with a full understanding of what symptoms occur when that food is ingested. Both are reliable when used appropriately and interpreted in the proper context."

You may hear alternative practitioners talk about diagnosing food allergies with other tests such as hair analysis, IgG tests (which measure immunoglobulin G, another antibody produced by the immune system), facial thermography and muscle testing. It's important to note that the National Institute of Allergy and Infectious Diseases' Guidelines for the Diagnosis and Management of Food Allergy in the United States says these tests "lack evidence demonstrating any value in diagnosing food allergies." They also can set you back a few hundred dollars each, and you might endanger your health with inaccurate results.

The gold-standard food allergy test is an oral food challenge done in partnership with your allergist, which may be done in conjunction with IgE and skin-prick tests. For an oral food challenge, you will eat small amounts of the suspected allergen and watch for a reaction in the safety of the doctor's office (with antihistamines and epinephrine on hand in case of serious reactions).

"Diagnosing food allergies is complicated and requires someone with proper training to obtain a detailed clinical history and interpret test results," Stukus says. "Self-diagnosing food allergy with home testing is filled with pitfalls and often leads to misdiagnosis and unnecessary food elimination. It also runs the risk of missing other conditions or factors that may have been the true cause of symptoms."

For food sensitivity

Unfortunately, there are no validated tests to diagnose food sensitivity, even though marketing leads consumers to think many test methods are accurate and reliable. Don't believe the hype.

Most of the excitement surrounds the IgG test (again, different from the IgE blood test), which is marketed as a way to identify hidden food sensitivities or intolerances. Stukus says this is not an evidence-based recommendation, and the IgG test is more likely to indicate the foods you commonly eat, not the ones causing you an issue. Studies show that IgG can be a marker of exposure to food and possibly of tolerance - the opposite of sensitivity.

If you suspect a food sensitivity, an elimination diet is the most reliable way to determine your trigger foods. In consultation with your doctor or dietitian, you will remove foods from your diet that you suspect are causing reactions such as gas and bloating. You will later reintroduce the foods one at a time, and keep track of symptoms to see which foods cause a reaction. And hey, no fancy kits to buy - regardless of the money-back guarantee.

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