Doubt cast on many reports of food allergies
New government study finds widespread misdiagnoses, misleading tests
By Gina Kolata
updated 1 hour, 34 minutes ago
Many who think they have food allergies actually do not.
A new report, commissioned by the federal government, finds the field is rife with poorly done studies, misdiagnoses and tests that can give misleading results.
While there is no doubt that people can be allergic to certain foods, with reproducible responses ranging from a rash to a severe life-threatening reaction, the true incidence of food allergies is only about 8 percent for children and less than 5 percent for adults, said Dr. Marc Riedl, an author of the new paper and an allergist and immunologist at the University of California, Los Angeles.
Yet about 30 percent of the population believe they have food allergies. And, Dr. Riedl said, about half the patients coming to his clinic because they had been told they had a food allergy did not really have one.
Dr. Riedl does not dismiss the seriousness of some people’s responses to foods. But, he says, “That accounts for a small percentage of what people term ‘food allergies.’ ”
Even people who had food allergies as children may not have them as adults. People often shed allergies, though no one knows why. And sometimes people develop food allergies as adults, again for unknown reasons.
For their report, Dr. Riedl and his colleagues reviewed all the papers they could find on food allergies published between January 1988 and September 2009 — more than 12,000 articles. In the end, only 72 met their criteria, which included having sufficient data for analysis and using more rigorous tests for allergic responses.
“Everyone has a different definition” of a food allergy, said Dr. Jennifer J. Schneider Chafen of the Department of Veterans Affairs’ Palo Alto Health Care System in California and Stanford’s Center for Center for Primary Care and Outcomes Research, who was the lead author of the new report. People who receive a diagnosis after one of the two tests most often used — pricking the skin and injecting a tiny amount of the suspect food and looking in blood for IgE antibodies, the type associated with allergies — have less than a 50 percent chance of actually having a food allergy, the investigators found.
One way to see such a reaction is with what is called a food challenge, giving people a suspect food disguised so they do not know if they are eating it or a placebo food. If the disguised food causes a reaction, the person has an allergy.