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There is a large correlation between a peanut allergy and a nut allergy. Although most people discussing food allergies tend to combine peanuts and tree nuts into one, on a basic biological level, the two are quite different. Peanuts are actually legumes and they grow in the ground. Tree nuts, which are truly nuts, grow in trees and include cashews, almonds, pecans, walnuts, pistachios, pine nuts, hazel nuts, Brazil nuts, macadamia nuts, and hickory nuts.
Despite the botanical differences between a peanut and a tree nut, there are some remarkable similarities for those suffering from nut allergies. First, both peanuts and tree nuts can cause extreme allergic reactions. Second, a person with a nut allergy can have a severe reaction with only the smallest exposure to the offending nut – just like the peanut. Third, typically, where one finds peanuts, there will also be tree nuts – common places for hidden nuts are in baked goods, candy, ice cream, and ethnic food. Fourth, both peanut oil and extract and tree nut oils and extracts have proteins that cause allergies.
Usually thirty to forty percent of the people with a peanut allergy also have a tree nut allergy. Basic research holds that both peanuts and tree nuts are potent allergens; consequently, they remain the highest among the foods that cause fatal reactions. Other research holds that there some structural similarities between the protein of the peanut and that of the tree nut. In general, a person who has a peanut allergy should also avoid tree nuts for fear of developing a tree nut allergy – and visa versa.
Typically, a reaction to peanuts has a greater chance of turning into anaphylaxis than a reaction to tree nuts. Anaphylaxis can appear within a few seconds of consuming a peanut or in rarer cases, a tree nut. The symptoms can last up to a few hours. It affects the skin, intestines, blood vessels, heart, and breathing passages of a person who has a peanut or a nut allergy. Itching, hives, vomiting, cramps, difficulty breathing due to swollen passages, and fainting may occur. In the worst cases, it could cause a deep, deadly shock.
In addition, both peanuts - to a greater degree - and tree nuts – to a lesser degree – can cause exercised-induced anaphylaxis. In those cases, a person who does not even know he has a food allergy eats the food, and then exercises. The same symptoms seen in normal food-induced anaphylaxis is seen; however, it can be hours after eating a peanut or tree nut. Consequently, an allergy exists; but, the person may have a hard time determining that he has a peanut or nut allergy because of the duration between the consumption of the food and the symptoms of the attack.
When I volunteered to provide snacks for my son's fifth grade class, the teacher gave me a list of guidelines to follow. Several of the items concerned the use of tree nuts and peanuts. I could make brownies with walnuts, but I also had to make another batch of walnut-free brownies and clearly label it. If I used peanut butter in a recipe, I had to make sure it was marked "contains peanuts". Some children were actually so allergic that contact with peanut shells alone could cause problems.
I managed to make enough snacks under those restrictions, but I couldn't help but feel sorry for the children who had to live their lives in fear of things like mulch and peanut shells. Even products that don't contain tree nuts or peanuts may have been processed n shared equipment.
I've seen warnings on peanut butter jars that say the production equipment may have also been used to process tree nuts. I figure that means a company may have produced almond butter in the morning and switched over to peanut butter in the afternoon. There's no way to guarantee the workers managed to remove all traces of the tree nuts before they started grinding the peanuts for peanut butter.
I wouldn't think there would be that much of a risk of cross-contamination, but apparently some people with a tree nut allergy might have a bad reaction if there was the smallest trace of almonds in their peanut butter. The nut butter processing companies have to put that warning on their products, because they know they can't make things 100% allergen free. If the consumer is made aware of the risks, then he or she can make an informed decision.
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