Leffler, who is a gastroenterologist at Havard University’s Beth Israel Deaconess Medical Center, also expects that the total population of Americans with celiac disease may increase to almost 2.5% in the next decade.
Think you have food allergies? Think again
The most commonly used tests can be inaccurate, leading some people to limit their diets needlessly.
By Emily Sohn
July 20, 2009
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."
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.
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."
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.
Not much has changed. Today, between one-quarter and one-third of people suspect an allergy in their children or themselves, even though rates are up to five times lower than that.
For some people, the problem is not an allergy but a more subtle sensitivity or intolerance. Lactose intolerance, for example, occurs when there's a shortage of the enzyme that breaks down milk proteins. About 50 million Americans have it, with symptoms after consuming milk products that include bloating, gas and diarrhea. The solution is simple: Avoid dairy, or supplement the diet with the enzyme lactase.
Gluten sensitivity, which is becoming more common -- in reality and also in people's perceptions -- is more complicated. It occurs when the body fights against gluten, a protein in wheat, barley and rye. At its worst, this sets off a cycle in which the body's immune system gets confused and attacks the small intestine. The result is celiac disease.
About one out of 133 people in the U.S. has celiac disease, though an estimated 90% of cases are currently undiagnosed. And rates are increasing. As many as 2.5% of the population will have celiac disease in a decade, predicts Daniel Leffler, a gastroenterologist at Harvard Medical School in Boston.
The good news is that celiac disease can be diagnosed with a blood test and intestinal biopsy. The bad news is that a large number of people don't have celiac disease and yet still feel lousy after eating gluten. Symptoms can be as vague as fatigue and stomach upset, possibly because gluten is a protein that is hard for everyone to digest. But there is no definitive intolerance test.
In that way, sensitivities to gluten resemble sensitivities to MSG, food dyes and nitrites. Some people insist they feel better without these chemicals in their diets. But scientists can't say for sure if they're right -- or whether what they're reporting is some kind of self-administered placebo effect. There are no data to help clear up the muddle.
"With most intolerances, there's nothing medically you can measure," Leffler says. "There's nothing you can see."
It's a natural human tendency to link ill feelings with whatever you ate last, says Marion Nestle, professor of nutrition, food studies and public health at New York University.
"It makes you feel better to know you've got something real," Nestle says. "It's awful to just feel awful."
It can't hurt to try a diet free of gluten, food dyes or MSG, experts say. The danger is when people eliminate one food after another in an attempt to get rid of symptoms that (perhaps coincidentally) wax and wane with those dietary changes.
Highly restrictive diets can be tough on people and their families. (There is food coloring even in some cheeses, and gluten in soy sauce.) They can also be unhealthy. To avoid malnutrition, fatigue or low bone density, doctors recommends people who start removing ingredients from their diets consult a nutritionist for advice.
"There's nothing magical about a gluten-free diet," Leffler says. "It's actually rigorous and difficult to follow. It's in processed meats, medications, dustings on frozen vegetables. It's everywhere. For people who have to follow a gluten-free diet, it's a huge, huge headache."
As scientists work to unravel the mysteries of the immune system, doctors recommend that people with suspected allergies or intolerances get to a specialist right away. It takes an average of 11 years to get diagnosed for celiac disease. No one should have to wait that long to feel better.