It turned out she had a potentially fatal allergy to sesame, a main ingredient in halvah. Today, if she bites into a plain bagel which so much as sat next to a sesame seed bagel in the bakery, she feels the reaction begin in her throat. Susan is allergic to tree nutstoo. And as an adult she has developedoral allergy syndrome, a reaction to certain fruit and vegetable proteins which resemble thepollen proteins responsible for hay fever allergies.
Today she carries an EpiPen®. Accidental exposure to one of the foods she’s allergic to can send her to the hospital.
Some people don’t get diagnosed, or even develop food allergies, until much later in life. Holly Caster was in her 30’s when she started noticing that eating a peach made the roof of her mouth itchy. Sometimes the sensation went up into her ears. A scratch test showed that she was allergic to stone fruits, and many nuts to boot. But Holly’s food allergies are less severe than Susan’s—for her, they’re an annoyance, not a life-threatening danger.
Food allergies may be one of the hottest topics in medicine, but they are also among the least understood. Horror stories of children dying from exposure to a particle of peanut can obscure some of the realities about these allergies. Let’s try to blow away a few of those clouds of peanut dust:
What exactly is a food allergy? Simply put, it’s an abnormal immune response to a food. But other situations, such as toxic reactions to spoiled food and lactose intolerance, can be mistaken for allergic reactions.
Real allergic reactions range from Holly’s tingling sensation in the mouth to Susan’s potentially fatal anaphylactic shock. Complicating the definition are related phenomena like exercise-induced food allergies and cross-reactivity between pollens and foods.
The National Institute of Allergy and Infectious Diseases estimates that out of some 30,000 episodes of anaphylaxis caused by food each year, 100-200 people die.
How common are food allergies? Depends who you ask. Dr. Matthew Fenton of the NIH’s National Institute of Allergy and Infectious Diseases says there’s a good deal of evidence of over-diagnosis by doctors, as well as over-self-reporting. Still, the odds a child has a food allergy are a pretty hefty 1 in 25.64, the exact same odds ( 1 in 25.64) a household owns a bird. And speaking of birds, the odds an adult is allergic to eggs are 1 in 500. Fish: 1 in 250.Shellfish: 1 in 50.
How accurate are the tests? Another thorny question. When a skin or blood test identifies a food allergy, much of the time it’s effectively a false positive, since the presence of an antibody doesn’t necessarily indicate an allergy. According to Dr. Jennifer Schneider Chafen of Stanford University, co-author of a recent paper that reviewed more than 70 food allergy studies, about 1 in 12.5 people would test positive for a peanut allergy. Yet the odds an adult is actually allergic to peanuts are only 1 in 166.7.
Currently, only a “challenge test”—giving a patient tiny amounts of a suspected allergen in a controlled environment—can definitively prove an allergy, according to pediatric allergist Dr. Robert Wood of Johns Hopkins. A new test under development at MIT analyzes individual immune cells. It would be less demanding of the patient than a challenge test and more pleasant than common skin patch tests. Better tests would lead to more confident eaters and less fear. For years Susan thought she was allergic to strawberries and never touched them. After more testing it turned out she could have been enjoying strawberries all along.
What other foods are people allergic to?Tree nut allergy afflicts 1 in 200 adults. (Cashews, almonds, and walnuts are tree nuts; peanuts are legumes, not nuts.) Sesame triggers reactions in some people. Others are allergic to soy or wheat, two of the most common foods in our diet. And while lactose intolerance is common, 1 in 333.3 adults is actually allergic to milk.
Do people grow out of food allergies? Depends what food. Remember those 1 in 333.3 adults allergic to milk? Well, for children under 3 those odds were a much higher 1 in 40. All told, the odds a child younger than 3 has a food allergy are 1 in 16.67—but the odds then drop to 1 in 27.03 for kids between 5 and 17.
But most people don’t grow out of tree nut allergies. Peanut allergies, too, are usually lifelong, and can be so dangerous the US government is considering banning peanut snacks on all airline flights. Closer to home, more children with peanut allergies mean more hassles for schools that provide lunches. The Brandon, SD schools are typical: their effort to purchase only nut-free ingredients is about to give way to a system of preparing meals separately for allergic kids.
How are food allergies identified and treated? Usually with an elimination diet—completely removing suspected foods from the diet, then gradually introducing other foods, observing what causes a reaction, and eliminating that food from the diet permanently. But the Stanford researchers found only one randomized controlled study of that treatment.
Immunotherapy (gradual acclimation) shows promise; British researchers say they’ve effectively cured children of peanut allergies this way.
But for now, the only reliable way to avoid an allergic reaction is to avoid the foods you’re allergic to…after you’ve determined for sure what they are.
Add a comment
