Allergic to one type of nut? You may not have to avoid them all, study suggests

Why you should eat nuts
Allergic to walnuts? It doesn't mean you're allergic to all tree nuts, a new study suggests. BSIP/UIG via Getty Images

If you’re allergic to one type of nut, chances are high that you’re avoiding all types of nuts. Now, new research suggests that people with a single nut allergy may be able to eat other types even if a blood or skin prick test tells you otherwise.

The key is to try an oral food challenge – this is when an allergist feeds patients with tiny amounts of a specific food in increasing doses over a period of time to see if allergies are triggered.

The researchers behind the study out of the American College of Allergy, Asthma and Immunology say that this is the best way to tease out which nuts are safe.

READ MORE: Did dated recommendations contribute to the spike in food allergies in kids?

In their findings, half the people who were allergic to one nut and tested positive to being allergic to others, passed oral food challenges to other tree nuts without a reaction.

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“Too often, people are told they’re allergic to tree nuts based on a blood or skin prick test. They take the results at face value and stop eating all tree nuts when they might not actually be allergic,” Dr. Christopher Couch, an ACAAI allergist and study lead author, said.

“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,” Dr. Matthew Greenhawt, another study co-author and allergist, explained.

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About 109 people with nut allergies took part in the ACAAI study. But the study authors are warning: if you’re curious about whether you’re truly allergic to all nuts, you need to do a food test with a trained, board-certified allergist.

If you’re in the clear for certain nuts, there’s a possibility they could be weaved into your diet, they said.

“The practice of avoiding all peanut and tree nuts because of a single nut allergy may not be necessary,” Greenhawt said.

Peanut allergies and tree nut allergies aren’t the same. Keep in mind, peanuts are legumes, not nuts.

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Still, between 25 and 40 per cent of people who are allergic to peanuts also react to at least one tree nut, the ACAAI says.

READ MORE: 5 common food allergies: How much is enough to trigger a reaction?

Tree nuts include almonds, Brazil nuts, cashews, chestnuts, hazelnuts, macadamia nuts, pecans, pistachios and walnuts, among others.

People who are allergic to some tree nuts tend to avoid others because of the risk of cross-contamination, according to Beatrice Povolo, director of advocacy at Food Allergy Canada, a national non-profit dedicated to helping people with food allergies.

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“Not everyone who is allergic to peanuts is allergic to tree nuts, and not everyone who is allergic to a tree nut is allergic to all tree nuts,” she told Global News.

“The issue is when people are managing their allergies, there is potential for cross-contamination if a product is being manufactured or if people are dining out,” she said.

For some people with allergies, all it takes is trace amounts to trigger a severe reaction, she noted.

READ MORE: What doctors are warning about parents about allergies and asthma in kids

Right now, about seven per cent of Canadians have food allergies. Other research suggests that food allergies in babies is on the rise, affecting more than 10 per cent of one-year-olds.

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The number of people who have a food allergy in general is on the rise, but there’s no clear-cut answer as to why.

The ACAAI study was published this week in the Annals of Allergy, Asthma and Immunology.