Unfriendly foods--how great is the threat of food allergy?

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There's a new villain in town. The seemingly benign peanut has become public food allergy enemy number one.

In response to several occurrences of peanut mislabeling and the specter of severe reactions by people who are allergic, manufacturers are scrambling to list peanuts as an ingredient on food labels, even if it is present only in minute amounts. But new worries arise from allergic reactions attributed to inadvertent cross-contamination of a nonpeanut-containing food with traces of peanuts during manufacture or transportation.

Still, food allergies are much less common--though potentially more serious--than you might think. One survey estimated that up to 40% of adults believe that they or some member of their family suffer from food allergies. In reality, only 1% to 2% of adults and about 5% of children demonstrate true food allergy.

Food intolerances, food poisoning, and even psychological aversions to food are often mistaken for food allergies. A true allergic reaction, however, is the result of a very specific sequence of events in the body.

Allergy: The Immune System Gone Wrong. Your immune system is the primary line of defense against microorganisms that can cause disease. Bacteria and viruses contain proteins, called antigens, that are foreign to your body. When first confronted by a harmful antigen, your body responds by forming antibodies, called immuno-globulins, specific to that antigen. During future attacks by the same antigen, these antibodies quickly mobilize forces to destroy the invading microorganism. So far, so good.

But nature is far from perfect. An allergy occurs when your immune system mistakenly identifies a harmless substance as a potentially harmful antigen. The resulting antibodies--typically immunoglobulin E (IgE)--coat cells in the stomach, lungs, upper respiratory tract or skin. No harm is done the first time you're exposed. It's subsequent times you encounter the allergen that cause trouble. The allergen binds to the antibodies your body produced the first time, causing release of histamine and other chemicals that trigger allergy symptoms. So, just because you've eaten a food before with no problem doesn't mean you're not allergic to it. It may take several encounters before an allergy reveals itself.

What to Expect if You're Allergic. The part of the body affected and the severity of symptoms vary from person to person. They may include:

Skin -swelling of lips, mouth, tongue, face or throat; redness or rash; hives; itchy skin or eyes.

Nose, Throat, Lungs -stuffy or runny nose; sneezing; coughing or wheezing.

Stomach, Intestines -abdominal pain or cramping; bloating or gas; nausea and vomiting; diarrhea.

Unfortunately, an allergy can first make itself known by provoking an anaphylactic reaction, a sudden, severe allergic reaction that demands immediate treatment for a sharp drop in blood pressure and breathing difficulty caused by swelling of the tongue and throat. This can develop as quickly as a few seconds after eating or may take minutes to occur. An anaphylacticreaction is not to be taken lightly. It can be fatal if not treated immediately, usually with an injection of epineph-rine (adrenaline).

Growing Older With Food Allergies. Although it is theoretically possible to be allergic to almost any food, 90% of allergies are to the same few foods:

Cow's milk
Eggs
Fish and shellfish
Nuts
Peanuts
Soy protein and other legumes
Wheat
Children tend to be more allergic than adults. Many people, however, eventually outgrow allergies to cow's milk, eggs, soy and wheat, so there is often no need to avoid them for life.

But people don't usually outgrow allergies to peanuts, tree nuts (such as walnuts or cashews), fish and shellfish. Unfortunately, these are the foods most likely to cause severe reactions. Experts note that hypersensitivity to peanuts and tree nuts are the leading causes of fatal and near-fatal food-induced anaphy-lactic reactions. Extremely sensitive individuals can develop symptoms by simply touching or smelling a food to which they are allergic.

A Multitude of Food Allergy Tests. Allergies can be distinguished from other negative food reactions by the presence of antibodies.

Skin tests are the traditional method of diagnosis. An allergy specialist injects extracts of various food proteins under the skin. The appearance of a round bump indicates a reaction and possible allergy. A negative skin test--indicating no allergy to the tested food--is usually accurate. Unfortunately, skin tests often over diagnose food allergies, giving false positive results (indicating an allergy when one really doesn't exist) as much as 65% of the time.

Blood tests for allergy include the radioallergosorbent test (RAST), and enzyme-linked immunosorbent assay (ELISA). Both tests are expensive and require expert interpretation, so are best done by a physician who is board-certified in allergy.

Food challenges require you to eat a small amount of the suspect food and then be observed for a reaction. To be accurate, a food challenge should be controlled by a placebo (you don't know if you're consuming the suspect food or a look- and taste-alike fake). It should also be "double-blind" (neither you nor the person giving the test knows which is the suspect food and which is the placebo).

What to Do. Allergy shots are not recommended for food allergies because the shots themselves can trigger severe reactions. Antihistamines can be effective in some cases, but that must be determined by trial and error.

People at risk for severe reactions, because they have suffered previous severe reactions or have a history of asthma or multiple allergies should carry an emergency Epi-Pen or Ana-Kit, to self-administer epinephrine.

The only sure way to treat a food allergy is to identify the offending substance and avoid it completely. That's easier said than done, especially in the case of peanuts, which are "hidden" ingredients in many foods.

In the meantime, if you have a food allergy, check labels every time you buy a food, because companies can change ingredients without warning. Especially, become familiar with words and phrases that indicate the presence of an allergen. (See below.)

The Perilous Peanut
Peanut allergies are on the increase, says Hugh Sampson, M.D., of Johns Hopkins University School of Medicine. He suggests it's due to all the peanut-containing products children eat before age three, when their immune systems may not be mature enough to handle the peanut protein. This, then, becomes a lifelong allergy.

Avoiding peanuts is tricky. They can be hidden in foods you would never suspect, for example: Chinese dishes, chili, spaghetti sauce, gravy, ice cream and enriched cocoa, where they may be in powdered form as a thickener.

People who are extremely sensitive can react simply from cross-contamination, such as Chinese food cooked in a pan previously used to cook a peanut-containing dish. Don't take chances if you are allergic to peanuts. Read labels carefully and ask lots of questions.

Ingredient List Terms
If you are allergic to any of the following foods, look for these words and prefixes in ingredient lists on food labels so you'll know what to avoid:

Cow's Milk: butter, casein, cheese, chocolate (may contain milk solids), cream, curds, lacta-, lacto-, milk, whey, yogurt.

Wheat: bran, bread, cereal extract, farina, flour, gluten, graham, hydrolysates, malt, modified food starch, starch, wheat.

Soy: hydrolyzed vegetable protein, lecithin, miso, modified food starch, soy, tempeh, textured vegetable protein (TVP), tofu, vegetable protein concentrate.

Peanuts and Nuts: specific peanut or nut name (e.g. cashews, walnuts), nut meats.

Egg: albumin, egg, globulin, livetin, ova-, ovo-, vitellin, white, yolk.

Fish and Shellfish: specific fish or shellfish name, imitation crab or lobster (surimi).

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By Mary Carole McMann, M.P.H., R.D.

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