An estimated two point five million Canadians is allergic to a least one food. For many, that means cashews, pecans and other kinds of tree nuts. If your doctor told you to stay away from all of them, there may be some good news, thanks to a new study.

Let's start with the basics. There are lots of tree nuts. They include almonds, Brazil nuts, cashews, chestnuts, hazelnuts or filberts, hickory nuts, macadamia nuts, pecans, pine nuts, pistachio nuts and walnuts. Health Canada considers tree nuts a priority allergen. There are food sources that contain tree nuts. These include amaretto liqueurs, baked goods such as biscotti, cookies and crackers, barbecue sauce, granola, muesli, health food supplements, herbal teas, hot cocoa, ice cream, main course dishes, natural flavourings, nut-flavoured coffee, peanut oil, pesto sauce, smoke flavourings, spreads and nut butters.

And let's not forget that some non-edible products contain tree nuts. These include beanbags, birdseed and other pet food, massage oils and cosmetics round out the list.

Here is a link to an information sheet from Food Allergy Canada.

The study - published in the journal Annals of Allergy, Asthma & Immunology - looked at 109 people with a known allergy to a single kind of tree nut. Fifty-four were allergic to almonds, 28 to cashews, 27 to walnuts, 18 to hazelnuts, 14 to pecans, 13 to pistachios and two to Brazil nuts. The patients had skin or blood testing for allergies to other tree nuts. Fifty-four of the patients in the study had an actual allergy – meaning they had symptoms of an allergy and positive testing. Forty-three of them had a positive test but no allergic symptoms. The remaining 13 had been avoiding tree nuts despite negative allergy testing. You can find the study by following the links to the current issue here.

Participants in the study were tested with what's called an oral food challenge. This is a controlled test in which the patient eats tiny amounts of the food being tested while being observed in the clinic for allergic symptoms. If they tolerate the food, they are tested with an increased dose of the food. Passing an oral food challenge means you are not allergic to the nut.

Despite showing sensitivity to other tree nuts, more than 50 per cent of those tested had no reaction to an oral food challenge. In the case of almonds, 100 per cent of the patients passed.

The study's authors speculated on why patients with nut allergies may have been getting the wrong advice.

As part of the work up, patients with an allergy to tree nuts or peanuts typically receive a battery of skin tests. Often, these show they are sensitive to a range of tree nuts. Does that mean they are allergic to all of them? Not necessarily. It may have to do with how allergy skin testing is interpreted.

In a scratch test, a tiny extract of the allergen enters the skin. A positive test means that skin erupts in a small bump or wheal 2 mm in diameter or greater. The authors of the study say maybe it should be 3 mm or greater, which would cut down on the number of false positives.

Some doctors might be telling patients with positive skin tests that they're allergic because they don't know better. Or, they may be responding to patient or parental anxiety to "play it safe" by avoiding all tree nuts. In particular, many doctors routinely advise patients with peanut allergy to avoid all nuts to which they have positive skin testing.

Most of us want to play it safe. Still, it comes down to a balance of benefit versus risk. If the risk of an allergic reaction is great, then the benefit would have to be substantial to take a chance. On the other hand, if the risk is low, then all we're doing is telling patient not to eat foods that contain valuable nutrients. Tree nuts are rich in unsaturated fats, vegetable protein, fiber, minerals, and antioxidants. They have proven health benefits. They reduce oxidative stress and inflammation. They help lower blood pressure and reduce triglycerides. They help reduce the risk of heart attack and stroke.

And let's not forget that the play it safe attitude especially involves children. No doubt there will be parents who want to put tree nuts into their kids' lunch boxes. But again, that raises legitimate concerns for other kids who have proven allergies.

What should you do?

If you've are allergic to a particular tree nut, avoid that tree nut in all forms. By the way, the symptoms of an allergy include abdominal pain, cramps, nausea, vomiting, diarrhea, difficulty swallowing, itching of the mouth, throat, eyes or any other area, nasal congestion, shortness of breath, wheezing, and anaphylaxis.

If you don't have a proven allergy to other kinds of tree nuts, speak with your doctor. If you've avoided all tree nuts simply because you had positive blood or skin testing only, and you want to know for sure, see your allergist about an oral food challenge. There's a reasonable chance that you can tolerate one or more tree nuts, especially almonds. If you do try this with the support of your doctor, remember to always carry an Epi-Pen with you at all times.

Playing it safe no longer means that you must say no to some very nutritious foods.