Q. I suspect I have some food allergies and I want to have some tests done. What test should I start with?
A. Although the term “allergy” originally meant an “altered response,” physicians and researchers now use the term to designate only the type of allergy that involves Immunoglobulin E antibodies and the release of histamine. This type of allergic response is indeed the easiest to identify and is potentially life threatening. However, it is more often evoked by airborne allergens than by food.
About 25% of people think they are allergic to foods, but the incidence of IgE mediated allergy to foods is low, probably from 1% to 2%. However, by including “food intolerance” in the definition of food allergies, Alan Gaby M.D. estimates that 60% of the U.S. population suffers from some reaction to a food that can cause or complicate a health problem. An Immunoglobulin G mediated immune response is the most common cause of food intolerance, but because symptoms are often delayed for many hours and people might be unable to associate their symptoms with the foods they eat, such food allergies are underdiagnosed. This type of food allergy or intolerance might not result in histamine release but might instead trigger the release of other inflammatory substances.
For years the gold standard for identifying food sensitivities has been the “elimination and challenge” diet. This entails a careful elimination of one or more foods from your diet for at least a week, then a systematic return of each food, one per day, with careful observation of your response. The week of avoidance allows all traces of the food to leave your body and for your body to adjust to being without that food. This makes your response to the subsequent challenge of eating the food easier to interpret.
Testing for blood levels of IgG antibodies to a variety of foods is available. Testing makes it possible to reduce the number of foods you avoid in the elimination and challenge diet. The blood test by itself is only about 50-80% accurate and still needs the confirmation of the elimination and challenge diet.
Identification of offending foods is essential for effective treatment, which primarily is strict avoidance of the food. Studies have shown that approximately one-third of food allergy sufferers lose their reactivity to an offending food after one to two years of avoidance. Excessive exposure to a particular food may affect the overall rate of allergy to that food in a population. This is seen in the high incidence of fish allergy among Scandinavians and of rice allergy among the Japanese. In America the common culprits are the commonest foods on the American menu: milk, wheat, eggs, soy, corn, etc.
Symptoms of food allergy are so varied as to be virtually useless in deciding whether or not a person has food sensitivity. One source lists 67 complaints that have been associated with food intolerance.
Although heredity seems to be the prime reason some people have allergies and others don’t, there is an ever-expanding list of diseases related to disruption of the immune system. An important concern is the possibility that the chemical soup created by our civilization drives the immune system into an “allergic” state and thus produces this variety of diseases.
This article appears in February 20 • 2004.