Going Nuts Over Food Allergies? Doctors' Recommendations May Be Too Strict

Sometimes you feel like a nut, sometimes you don't. But a new study suggests that many people may be avoiding nuts altogether because they've been diagnosed with allergies that they don't actually have.

The paper, published in the Annals of Allergy Asthma, and Immunology, examined the results of patients who were tested for tree nut allergies — which include almonds, cashews, pecans, Brazil nuts, walnuts and hazelnuts, but not peanuts — with two different methods. The first is a skin prick test, which measures sensitivity to a small amount of the allergen, and the second is a oral food challenge, in which the patient actually consumes the food.

The oral test is much more accurate than the skin prick test, the study's press release notes: "Passing an oral food challenge means you aren't allergic to that nut."

"Too often, people are told they're allergic to tree nuts based on a blood or skin prick test," says allergist Dr. Christopher Couch, a diplomate with the American Board of Allergy and Immunology and lead author of the study.

Usually, this happens because the patient has a real allergy to one kind of nut. Doctors sometimes recommend these patients avoid all nuts to be safe, or they direct the patients to take the potentially inaccurate skin prick tests.

"They take the results at face value and stop eating all tree nuts when they might not actually be allergic," Couch said. "We examined records of 109 people with a known tree nut allergy to an individual nut. They were tested for other tree nuts they had never eaten before using blood or skin prick tests. Despite showing a sensitivity to the additional tree nuts, more than 50 percent of those tested had no reaction in an oral food challenge."

Any test of an allergy should be conducted in a controlled setting and in coordination with one's doctor.

"Previous studies suggested people with a tree nut allergy, as well as those with a peanut allergy, were at risk of being allergic to multiple tree nuts," said allergist Dr. Matthew Greenhawt, chair of the American College of Allergy, Asthma and Immunology Food Allergy Committee and co-author on the study. "We found even a large-sized skin test or elevated blood allergy test is not enough by itself to accurately diagnose a tree nut allergy if the person has never eaten that nut. Tree nut allergy should only be diagnosed if there is both a positive test and a history of developing symptoms after eating that tree nut."

Photo credit: Steve Parker