Prevention & Recovery
Food allergies: Symptoms, causes, testing and treatment
Prevention & Recovery
Food allergies: Symptoms, causes, testing and treatment
When she was seven years old, Susan Hickman, 57, from Ottawa, moved to the coastal town of Sept-Îles, Que., where shrimp was part of her everyday cuisine – and in her favourite dish, shrimp fried rice. But as much as she adored shellfish, at 28, Susan developed a life-threatening allergy to all types of shellfish. Now eating even the tiniest morsel of her favourite food could kill her.
Between three and four per cent of Canadian adults, and nearly six per cent of children, suffer from food allergies, says Dr. Susan Waserman, an associate professor of medicine at McMaster University in Hamilton. And for unknown reasons, the numbers are growing. Although most people with a food allergy have non-life-threatening symptoms, such as a skin rash, itchy throat or gastrointestinal upset, everyone has the potential to develop severe, extreme reactions similar to Susan’s, says Waserman.
Unfortunately, there is no way to predict who will develop food allergies or progress to getting life-threatening reactions. In Susan's case, her ability to eat shellfish changed abruptly in the late 1970s, when she was living in Sault Ste. Marie, Ont., working at a newspaper. One night she was at a Chinese restaurant eating a beef-and-green-pepper dish; later that evening, red itchy hives broke out all over her face and mouth, and her throat swelled so much she was gasping for air.
"I went to the hospital, where I was treated for an allergic reaction," says Susan, who had never been aware of having allergies before. The whole event came as a shock, and she had no idea what triggered it. It took more than a year, and two additional near-death experiences, before she discovered shellfish was the culprit. Looking back she guesses that the beef dish must have been made with oyster sauce, which is common in many Chinese dishes.
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How do allergies happen?
To be allergic to something, your immune system must become sensitized to it, says Waserman, who explains that blood contains antibodies (cells that are part of your immune system), which normally fight invading organisms such as bacteria or viruses. Among these is an antibody called IgE, whose role is to identify substances, such as parasites, that should be attacked. For unknown reasons, IgE sometimes becomes programmed to identify something else – such as a protein from a specific food – as a substance that needs to be destroyed.
IgE sits on special cells called mast cells, which are filled with different types of granules containing chemicals. "If you're allergic to peanuts and accidentally eat something containing them, IgE recognizes the peanut allergen and binds to it," explains Waserman. This causes the mast cell to burst apart and discharge its army of chemicals. These chemicals then cause the symptoms seen in an allergic reaction to food, including hives, itchy skin, vomiting, lip and tongue swelling, shortness of breath and even low blood pressure.
Since food allergens get into the blood, they can travel anywhere in the body. That is why, when you eat a food you are allergic to, hives can appear on any part of your body.
Food allergies versus food intolerances
It's important to distinguish a true food allergy from a food intolerance. This is because allergies have the potential to progress to something life-threatening. Food intolerances (or food sensitivities) can be very uncomfortable, but it's highly unlikely they will kill you.
Since people often don't know the difference between an intolerance and a true allergy, they may not get appropriate treatment. But the two are very different beasts, says Waserman. Food intolerances have a huge variety of causes, ranging from a lack of certain digestive enzymes (as in lactose intolerance), abnormalities in the structure of the bowel or intestines (as in irritable bowel syndrome) and inherited conditions; they rarely involve the immune system.
With a true allergy, an adverse reaction to a food occurs more quickly than one from an intolerance; symptoms can start within minutes or even seconds. A food allergy reaction often includes itchy skin and swelling of the throat.
If you develop any sort of reaction to a food, says Waserman, you'll need to get tested by an allergist to find out whether or not the problem is an allergy. Allergists commonly do skin tests, which involve placing a small drop of allergen on the skin and then pricking the skin through it to see if there is a reaction, such as a hive and surrounding redness. Another test is the oral food allergy challenge: In a medically controlled environment, you are given increasing amounts of suspect foods to see if and how you react to them.
Many different foods can cause allergic reactions, but the top foods people are allergic to are shellfish, fish, peanuts (a legume, not an actual nut), eggs, milk, tree nuts (which includes everything from almonds to pine nuts to walnuts), wheat, soy and sesame seeds.
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The deadly reaction Susan suffers is anaphylaxis – an extreme response that involves multiple organs and systems in the body, including the skin, lungs, heart and respiratory system. Reactions often start with itchiness and swelling in the mouth, on the skin and in the throat, and rapidly progress to trouble breathing. Blood vessels expand, leading to a deadly drop in blood pressure, which causes the heart to stop. Anaphylaxis is triggered when the IgE antibody recognizes something it has identified to attack, and the immune system goes into overdrive to deal with it. The nonprofit support group Anaphylaxis Canada notes that up to two per cent of Canadians live with the risk of anaphylaxis – some from wasp or bee stings, others from specific foods.
Julie Kartzewski from Burnaby, B.C., is more than familiar with anaphylaxis. She's been hospitalized with it nearly a dozen times due to a nut allergy. When she eats a food she's allergic to (always unintentionally), she feels itchy all over, her mouth and throat swell, her eyes and lips get puffy and hives break out over her face. "Then I get a tightening in my chest and it becomes difficult to breathe," she says. As soon as the early signs of trouble occur, she injects herself with a device she carries around – an epinephrine auto injector – then immediately heads to the nearest emergency room. Two products, EpiPen and Twinject, contain epinephrine, a drug that gives the heart a temporary boost (for about 30 minutes) – just long enough for most people to get to a hospital.
A surprisingly difficult aspect of having a food allergy is avoiding the food, since it's often a "hidden" ingredient. Julie had her last anaphylactic reaction when she bit into an éclair in which the whipped-cream filling had been mixed with almond paste. Another time she ate pesto that had walnuts as an ingredient.
"You get used to reading food labels," she says. But even then you have to be careful; an ingredient can be listed under different names. For instance, whey is a milk product and can wreak havoc in people with a milk allergy.
How to avoid attacks
Avoiding foods you're allergic to, reading labels and carrying an epinephrine auto injector are key strategies for people living with food allergies, says Dr. Peter Vadas, an allergist, immunologist and associate professor of medicine at the University of Toronto and director of the division of allergy and clinical immunology at St. Michael's Hospital.
At restaurants, it's important to ask staff about food ingredients and how something is prepared. You need to be wary of imported foods, too, since food-labelling laws vary among countries, and accuracy can't be guaranteed. For instance, Vadas says, labels on chocolate bars from Europe often don't say they may contain peanuts.
Because of her extreme allergy, Susan, who loves eating out, often avoids it. She hates living with an extreme allergy and says that asking servers in restaurants detailed questions about ingredients or how food is prepared makes her feel like a fussy customer. Then again, even the tiniest exposure could be a death sentence.
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Who's most at risk?
In Canada, deaths from severe food allergies are rare, thanks to epinephrine auto injectors and increased awareness. But deaths do happen, especially among teens and young adults. "This group takes the highest risks," says Vadas. These people might think they can get over a food allergy, or they're in denial and keep eating the food that makes them sick. "The people who die typically don't have a rescue medication [epinephrine] with them."
Children are at lower risk of death because of attentive parents and growing awareness in schools. Older adults have a lower risk because they are more careful, and because food allergies are most prevalent in children, and less so in adults.
The bottom line for food allergy sufferers is be alert about what you eat at all times, and carry an epinephrine auto injector.
The scoop on food intolerances
Food allergies and food intolerances are not the same. A food allergy results from part of the immune system reacting to a specific protein in the food you're allergic to. Food intolerances (sensitivities) result from a large number of medical conditions, most of which have nothing to do with the immune system. Dr. Peter Vadas, an allergist, immunologist and associate professor of medicine at the University of Toronto, explains the types of food intolerances.
A low level of a digestive enzyme causes one type of intolerance. For instance, people with low levels of the enzyme lactase cannot properly metabolize lactose, a sugar found in milk. For them, eating milk products results in diarrhea, cramps, gas and bloating.
Some food intolerances, such as irritable bowel syndrome, are a result of a digestive tract that doesn’t function well. People with this problem can’t digest foods properly.
Then there are chemical sensitivities. For instance, caffeine, alcohol, chocolate or certain compounds in wine are known to trigger migraines in some people.
There are also inherited conditions, such as G6PD deficiency (favism), in which people lack the enzyme G6PD, which supports the health of red blood cells. For those without this enzyme, eating fava beans leads to the destruction of red blood cells.
A small number of food intolerances involve parts of the immune system – but not the parts connected to allergies. For instance, children with intolerances to certain foods, such as milk, eggs or soy, may suffer an eczema flare-up. Another example is celiac disease. People with this condition have an immune system that attacks the small intestine when they eat gluten, a compound found in wheat, barley and rye.
Food intolerances are more common than true food allergies. Avoiding the culprit food is key to staying well. Treatment depends on what the underlying condition is.
Tips for living with food allergies
• Get tested by an allergist to determine if you have a true food allergy.
• Learn the various names of the foods you're allergic to.
• Read food labels. Call toll-free numbers on food package labels. Ask manufacturers about ingredients and food preparation.
• Avoid foods that "may contain" the food you're allergic to.
• See a dietitian. Get advice on what foods your allergen might appear in and tips on eating out and eating a balanced diet.
• Be cautious in restaurants and at take-out counters. Ask staff about food ingredients and the risk of cross-contamination. For instance, is the same cutting board that's used for fish also being used for non-fish food?
• Always carry your epinephrine auto injector. Learn to use it. Train others how to use it on you, in case you cannot manage.
• Wear a Medic-Alert bracelet.
• Tell family and friends what you're allergic to.
• Get additional information from patient support groups such as Anaphylaxis Canada and the Allergy Asthma information Association.
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