Food Allergies

Posted on: Mon, 07/17/2006 - 10:03am
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Food Allergies

July 17, 2006, 02:10 PM

By Charles Stuart Platkin

Food allergies are serious business. In fact, according to Michael C. Young, M.D., assistant clinical professor of pediatrics at Harvard Medical School, approximately 11.4 million Americans (4 percent of the general population) have food allergies -- 90 percent of which are peanut and tree nut allergies. And food allergies lead to about 30,000 emergency room visits and 150 to 200 fatalities per year.

How do you know you have a food allergy?

It's tricky to identify an allergenic food after an isolated reaction. The usual culprits should be considered: peanuts, nuts, seeds, fish and shellfish. If more reactions occur, there is typically a pattern that makes the offending food easier to identify, says Anna Nowak-Wegrzyn, M.D., a professor specializing in pediatric allergy and immunology at the Mount Sinai School of Medicine. Diagnosis requires a combination of investigative work (trying to pin down the foods) and laboratory testing, such as skin prick tests and measuring antibody levels. "Frequently oral food challenges [feeding with the suspected food under physician supervision] are needed to conclusively establish the diagnosis," adds Nowak-Wegrzyn.

How do you know you're having an allergic reaction?
"Allergic reactions typically occur within minutes to no more than one to two hours after ingestion and contact with the food," says Young. The symptoms are as follows: Nearly all -- 90 percent -- produce skin reactions, about half -- 47 percent -- induce respiratory or multi-organ system responses, some -- 35 percent -- result in gastrointestinal symptoms, and about 20 percent result in anaphylaxis requiring epinephrine, he adds.

What's the difference between food intolerance and food allergies?

Allergic reactions are immunologic responses to food proteins that trigger the release of chemical mediators, such as histamines, which result in allergic symptoms: itching, rashes and hives, swelling, wheezing, vomiting, low blood pressure, anaphylaxis, etc. "Food intolerance results from the inability of the gastrointestinal tract to digest and metabolize components of the food," says Young. For example, in lactose intolerance, a deficiency of the enzyme lactase, which breaks down sugar in milk, results in GI symptoms, such as abdominal pain, bloating, nausea, vomiting, diarrhea or bloody stools.

What is happening biologically that creates a food allergy?

According to Young, "Genetically susceptible individuals are more prone to making immunoglobulin E (IgE) antibodies, which target specific food proteins. When the food proteins are ingested, these IgE antibodies bind to them and trigger the release of chemical mediators, such as histamine, from mast cells located in many tissues of the body, including the skin, lungs, circulatory system, digestive tract, mucous membranes of the nose, sinuses and throat." Histamine and other chemical mediators cause tissues to swell, itch and secrete mucus, airways to contract, blood vessels to dilate and blood pressure to drop, all effects of allergic reactions and, in the worst case, anaphylaxis.

What is anaphylaxis?

Anaphylaxis is an allergic reaction that can range from mild to life-threatening. It is most commonly seen as the effect of the rapid release of histamine, which, along with other released inflammatory signals, can cause hives/swellings (localized or all over the body), airway symptoms (throat itching or closure), cardiovascular symptoms (low blood pressure and dizziness), as well as gut symptoms (vomiting or cramping and diarrhea), says Jonathan Becker, M.D., a professor of medicine at the University of Washington and an allergy specialist. Anaphylaxis occurs in 40 to 50 percent of individuals with food allergies, adds Young.

What are the most common food allergies?

The eight most common (accounting for 90 percent of childhood allergies) are cow's milk, eggs, peanuts, soy, wheat, tree nuts, fish and shellfish. In children, allergies to milk, eggs and peanuts (in that order) are most common, whereas allergies to shellfish, peanuts and tree nuts are most common in adults, says Young.

Are some allergies worse than others?

Any food may cause fatal anaphylaxis, but peanuts and tree nuts have been identified as the most frequent causes of severe, life-threatening anaphylaxis, says Nowak-Wegrzyn.

How can you protect yourself if you do have food allergies?

There is no cure for food allergies, and the only way to prevent reactions is to avoid the offending food. Some must even avoid environmental exposures to the ingredients, such as nut oils or milk proteins in cosmetics, steaming of foods, etc.

Recently, the Food Allergen Labeling and Consumer Protection Act (FALCPA) was passed. It requires food manufacturers to list the major food allergens on ingredient labels. "Always read the label, even if you buy the product repeatedly, because the manufacturer may change the ingredients at any time. Pay attention to

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