Some Of The Newest Food Allergies Have Nonfood Triggers; How Best To Test

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When is a food allergy not a food allergy? When it's triggered by factors outside the food chain, like pollen or latex. The now-you-see-it, now-you-don't nature of such allergies, in which a person is allergic to certain foods only under certain conditions, makes them difficult to diagnosis and treat.

Although one in three Americans believe they are allergic to certain foods, experts think only about 1% to 2% of adults and 5% to 8% of children have true food allergies. Are the rest of those with itching, swelling and digestive upset merely imagining things? Of course not. The symptoms are real, but whether food is the trigger is a tricky call. Even physicians can mistake other conditions, such as food intolerances, food poisoning or irritable bowel syndrome, for food allergies. Part of the problem is the lack of foolproof diagnosis and the proliferation of questionable tests (see chart, page 6). Add to that the discovery of the following hide-and-seek food allergies: How Pollen Triggers Food Allergies. Oral allergy syndrome (OAS) has long been recognized as a problem in Europe, but is just now gaining attention in the United States. OAS strikes people who are highly sensitive to pollen. It is caused by the cross-reaction of allergens present both in pollen and in certain fresh foods, so that people allergic to pollen experience an allergic response when they eat these foods.

"Most primary-care doctors don't know about OAS," says Marianne Frieri, M.D., Ph.D., director of allergy and immunology at North Shore University Hospital in Manhasset, New York, "so they may not know to ask a patient who's had an allergic reaction to a food that typically triggers OAS whether they also have pollen allergies." The symptoms--limited to itching or swelling of the lips, tongue, roof of the mouth and throat--are much the same as in any severe food allergy. The difference is that OAS is triggered only by such foods as celery, tomato, potato, seeds, nuts and fruits.

In contrast, the eight foods that trigger 90% of traditional food allergies are peanuts, tree nuts (e.g. walnuts and pecans), fish, shellfish, eggs, milk, soy and wheat. While cooking food has no effect on the foods that cause traditional food allergies, heat usually destroys the protein component responsible for OAS.

Food Link to Latex. Anyone with long-term latex exposure--like healthcare workers, beauticians, food handlers, who all wear rubber gloves regularly--can develop a latex sensitivity.

Latex, which comes from a species of rubber tree, has proteins that are very similar to the proteins in foods like the banana, which grows on a similar species. Hence, latex-sensitive people can also be sensitive to bananas. Avocado and kiwi also can cause trouble, says Frieri. Others warn of reactions to chestnuts, potatoes and tomatoes.

Eating these foods won't always cause an allergic reaction in latex-sensitive people, but it's important to be aware of the possibility, especially since latex/food cross-reactions are reportedly on the rise. Strict avoidance of latex (using gloves made of an alternative material or low-allergen gloves) may help decrease the food sensitivity.

Even Exercise Can Trigger Reactions. Another unusual allergic reaction is food-dependent, exercise-induced anaphylaxis. (Anaphylaxis is a life-threatening hypersensitivity in which the chest and throat tighten, severely restricting breathing.) People who react this way after exercising have typically eaten a food to which they are allergic three to four hours before. As they exercise and their body temperature rises, they experience itching and light-headedness, which can lead to hives or wheezing, even anaphylactic shock.

According to allergy expert Hugh Sampson, M.D., of Mt. Sinai Hospital in New York City, the prevalence of food-dependent, exercise-induced anaphylaxis is on the rise. Athletic females are particularly vulnerable. To avoid reactions, don't eat culprit foods for four to six hours before exercising. The trick, of course, is identifying which foods are your potential offenders.

Labeling Loopholes. The best treatment is strict avoidance of offending foods. For some people, as little as 1/5,000 of a teaspoon is potentially fatal. Most allergens can be avoided by diligently reading ingredient labels. But one legal loophole still exists: Companies are allowed to list "natural flavorings" instead of specifying ingredients.

Then there is the new potential threat from genetically modified (GM) foods, which the Food and Drug Administration doesn't require to be labeled. The problem for people with allergies is that a GM food may contain an allergenic protein from a different species. Fortunately, only a fraction of the proteins in foods are potentially allergenic and genetic engineers do evaluate GM foods for allergenicity. However, they are required to do so only for the most common allergens.

Sampson, who has served on expert panels responsible for reviewing the allergenicity of bioengineered foods for both the FDA and the Environmental Protection Agency, does not yet believe there is cause for alarm. But the potential does exist for an unknown allergen to slip through, one reason EN advocates the labeling of GM foods.

Hope for the future may rest with vaccinations. Researchers at Johns Hopkins Medical Institutions in Baltimore have successfully vaccinated mice against peanut allergies, and others are working on a vaccination against shrimp allergy.

Food Allergy Resources
Food Allergy Network: (800) 929-4040; www.foodallergy.org. Good web site and cookbook with tips for shopping, substitutions and a glossary of ingredient terms.

American Academy of Allergy, Asthma and Immunology (AAAAI): (800) 822-2762; www.aaaai.org. Board-certified physicians.

American College of Allergy and Asthma: (800) 842-7777; www.allergy.mcg.edu. Physician referrals.

Asthma & Allergy Foundation of America: (800) 727-8462; www.aafa.org. Consumer newsletter, allergy-free food catalogs.

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By Dayna Winter, M.S., R.D.

Adapted by M.S., R.D.

HOW ALLERGISTS DIAGNOSE FOOD ALLERGIES
Food allergy attracts more than its fair share of unorthodox practitioners, so be wary of a quick diagnosis. A good allergy specialist conducts more than one test. Here is an overview.

Reliable
History: An allergist Should first obtain a thorough history from you. You may be asked to keep a written record of what you eat and when, plus symptoms.

Skin prick test: An allergist injects a small extract of food protein under the skin, then looks for a reaction. No reaction is a very reliable indicator of no allergy, but a positive reaction is not enough for accurate diagnosis. It is useful in conjunction with a good history and food challenge (see below).

Blood test: The most common blood test is called RAST (radio allergosorbent test). It is very expensive and less sensitive than skin testing, but is useful when skin is too irritated for skin prick tests or when skin testing poses too great a danger.

Elimination diet: All common allergens are removed from the diet, and then are reintroduced one by one to see if any provoke a reaction. This can take weeks to complete, but is helpful in identifying food culprits.

Food Challenge: The "gold standard" of food allergy, though rarely done because of the difficulty involved. Ideally performed in a hospital or well-equipped allergist's office to guard against an anaphylactic reaction. The patient takes a capsule of suspected allergen or placebo, then is observed for a reaction. Best if "double-blind" (neither the patient nor the doctor knows what's in the capsule).

Unproved
Cytotoxic blood test: White blood cells are mixed with dried extracts of suspect foods, then observed under a microscope. If the cells are altered in any way, it is assumed you are allergic to the food. There is no evidence the test is valid.

Sublingual provocation: Drops of an allergenic extract are placed under the tongue, then symptoms are observed. If a reaction is provoked, more injections of allergen are given to "neutralize" the response. There is no sound science to back up this test, and it could actually trigger dangerous symptoms.

Intradermal provocation: Similar to sublingual provocation, but the dose of the allergen is injected rather than placed under the tongue. Same lack of backup and worry about triggering symptoms.

Food immune complex assay: Touted to detect "hidden" food allergies. A blood sample is examined for food immune complexes (antibodies and antigens coupled together). There's no evidence such complexes correlate with food allergy.

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