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Think you have food allergies? Think again

The most commonly used tests can be inaccurate, leading some people to limit their diets needlessly.

July 20, 2009|Emily Sohn

Allergies were far from Christie Littauer's mind when she fed creamed spinach to her son Jack for the first time. The 6-month-old had already eaten peas and green beans. Why not try something more exciting?

"A few bites into it, he started wheezing," says Littauer, of Henderson, Nev. "He got bright red. Something was obviously wrong."

After a scary ambulance ride, Littauer later discovered that her little boy was allergic to dairy in the spinach, making him one of a growing number of people with known food allergies.

Follow-up tests pointed to a bunch of other allergies too, putting Jack in another large category: those who think (or whose parents think) they're allergic or intolerant to foods they can handle just fine.

For 2 1/2 years, Jack was shielded from a wide array of foods, until more accurate testing proved he could eat quite a few of them, including wheat and fish. That opened a menu of possibilities for Jack -- bread, pasta, even chicken nuggets.

With a glut of nonspecialist doctors now offering allergy testing to patients, results that can be difficult to interpret, symptoms that can be wide-ranging and people's insatiable need to find explanations for whatever ails them, foods are frequently blamed for crimes they did not commit.

Though allergies or intolerances (and recognition of them) do appear to be on the rise, there are far more people who erroneously think they have problems with specific foods.

"Every study has shown that the perception of having a food allergy is more often wrong than right," says Robert Wood, a pediatric allergist at Johns Hopkins University in Baltimore. "Only about 25% of people who think they have a food allergy will actually have one."

Many reactions

Between 6% and 8% of children under 3 are known to be allergic to at least one food. By adulthood, the number drops to about 3% or 4%, or about 12 million people in the U.S. Milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts account for 90% of food allergies.

Whether it's to pollen, penicillin, bees or strawberries, an allergic reaction involves an antibody called IgE (Immunoglobulin E) that is part of the body's normal attack against substances it senses as foreign.

In people with allergies, IgE triggers the release of histamines and other chemicals that can lead, within minutes to two hours, to a variety of symptoms, including itchy mouth, swollen tongue, hives, wheezing, skin rashes, nausea, vomiting and diarrhea. At its worst, the reaction is anaphylaxis -- a potentially life-threatening reaction that can occur within seconds and may lead to shock, airway closure and a blood-pressure drop.

In the case of food, these reactions appear to be happening more often than they used to. Exact comparisons are hard to come by, but some studies show a doubling of peanut allergies in the last five to 10 years in kids in the U.S., United Kingdom and Australia. A Mayo Clinic study published in June reported that celiac disease is now four times more common than it was in the 1950s.

For all food allergies, diagnoses in U.S. kids have increased by 18% in the last decade, according to the Centers for Disease Control and Prevention.

Inaccurate tests

As food allergies become more common, doctors struggle to figure out who actually has them. Testing is part of the problem: Common food allergy tests aren't very accurate.

The only sure-fire way to test for food allergies is with food challenges, in which patients consume controlled and increasing doses of a suspected food under careful supervision.

Yet doctors, especially primary care doctors who aren't allergy specialists, are far more likely to do blood tests, which are much less accurate and more difficult to interpret.

Experts have seen a proliferation of blood testing by primary doctors, a trend that leads to misdiagnoses of food allergies.

"We get patients coming in who are avoiding 20 or 30 foods based on blood tests," says David Fleischer, a pediatric allergist at National Jewish Health in Denver.

In a recent study, Fleischer and colleagues spent two weeks working with 125 children who had been diagnosed with a collective total of 60 food allergies. The kids, whose average age was 4, took a series of food challenges.

At the end of the study, presented in March at an allergy conference, the researchers were able to reintroduce at least four and as many as 20 foods into each child's diet. About 90% of the suspected allergies had turned up negative.

"People are so happy and appreciative when they can get more foods in," Fleischer says. "Even just one food allergy changes your life."

Celiac disease

There is no doubt that food allergies are real, serious and dangerous. At the same time, there is a long history of paranoia about food that lies more in the mind than the stomach.

In a 1987 study that followed nearly 500 children from birth to age 3, 28% of parents and caregivers thought their babies had adverse food reactions, though only 8% ended up having confirmed allergies.

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