Do you start itching whenever you eat peanuts? Does seafood cause your stomach to churn? Symptoms like these cause millions of Americans to suspect they have a food allergy.
But true food allergies affect a relatively small percentage of people: Experts estimate that only 2 percent of adults, and from 2 to 8 percent of children, are truly allergic to certain foods. Food allergy is different from food intolerance, and the term is sometimes used in a vague, all-encompassing way, muddying the waters for people who want to understand what a real food allergy is.
"Many people who have a complaint, an illness, or some discomfort attribute it to something they have eaten. Because in this country we eat almost all the time, people tend to draw false associations between food and illness," says Dean Metcalfe, M.D., head of the Mast Cell and Physiology Section at the National Institute of Allergy and Infectious Diseases.
The difference between an allergy and an intolerance is how the body handles the offending food. In a true food allergy, the body's immune system recognizes a reaction-provoking substance, or allergen, in the food--usually a protein--as foreign and produces antibodies to halt the "invasion." As the battle rages, symptoms appear throughout the body. The most common sites are the mouth (swelling of the lips), digestive tract (stomach cramps, vomiting, diarrhea), skin (hives, rashes or eczema), and the airways (wheezing or breathing problems). People with allergies must avoid the offending foods altogether.
Cow's milk, eggs, wheat, and soy are the most common sources of food allergies in children. Allergists believe that infant allergies are the result of immunologic immaturity and, to some extent, intestinal immaturity. Children sometimes outgrow the allergies they had as infants, but an early peanut allergy may be lifelong. Adults are usually most affected by tree nuts, fish, shellfish, and peanuts.
Food intolerance is a much more common problem than allergy. Here, the problem is not with the body's immune system, but, rather, with its metabolism. The body cannot adequately digest a portion of the offending food, usually because of some chemical deficiency. For example, persons who have difficulty digesting milk (lactose intolerance) often are deficient in the intestinal enzyme lactase, which is needed to digest milk sugar (lactose). The deficiency can cause cramps and diarrhea if milk is consumed. Estimates are that about 80 percent of African-Americans have lactose intolerance, as do many people of Mediterranean or Hispanic origin. It is quite different from the true allergic reaction some have to the proteins in milk. Unlike allergies, intolerances generally intensify with age.
For people with true food allergies, the simple pleasure of eating can turn into an uncomfortable--and sometimes even dangerous--situation. For some, food allergies cause only hives or an upset stomach; for others, one bite of the wrong food can lead to serious illness or even death.
Food intolerance may produce symptoms similar to food allergies, such as abdominal cramping. But while people with true food allergies must avoid offending foods altogether, people with food intolerance can often eat some of the offending food without suffering symptoms. The amount that may be eaten before symptoms appear is usually very small and varies with each individual.
Heredity may cause a predisposition to have allergies of any type, and repeated exposure to allergens starts sensitizing those who are susceptible. Some experts believe that, rarely, a specific allergy can be passed on from parent to child. Several studies have indicated that exclusive breast-feeding, especially with maternal avoidance of major food allergens, may deter some food allergies in infants and young children. (Smoking during pregnancy can also result in the increased possibility that the baby will have allergies.) Most patients who have true food allergies have other types of allergies, such as dust or pollen, and children with both food allergies and asthma are at increased risk for more severe reactions.
The greatest danger in food allergy comes from anaphylaxis, a violent allergic reaction involving a number of parts of the body simultaneously. Like less serious allergic reactions, anaphylaxis usually occurs after a person is exposed to an allergen to which he or she was sensitized by previous exposure (that is, it does not usually occur the first time a person eats a particular food). Although any food can trigger anaphylaxis (also known as anaphylactic shock), peanuts, tree nuts, shellfish, milk, eggs, and fish are the most common culprits. As little as one-fifth to one-five-thousandth of a teaspoon of the offending food has caused death.
Anaphylaxis can produce severe symptoms in as little as 5 to 15 minutes, although life-threatening reactions may progress over hours. Signs of such a reaction include: difficulty breathing, feeling of impending doom, swelling of the mouth and throat, a drop in blood pressure, and loss of consciousness. The sooner that anaphylaxis is treated, the greater the person's chance of surviving. The person should be taken to a hospital emergency room, even if symptoms seem to subside on their own.
There is no specific test to predict the likelihood of anaphylaxis, although allergy testing may help determine what a person may be allergic to and provide some guidance as to the severity of the allergy. Experts advise people who are susceptible to anaphylaxis to carry medication, such as injectable epinephrine, with them at all times, and to check the medicine's expiration date regularly. Doctors can instruct patients with allergies on how to self-administer epinephrine. Such prompt treatment can be crucial to survival.
Injectable epinephrine is a synthetic version of a naturally occurring hormone also known as adrenaline. For treatment of an anaphylactic reaction, it is injected directly into a thigh muscle or vein. It works directly on the cardiovascular and respiratory systems, causing rapid constriction of blood vessels, reversing throat swelling, relaxing lung muscles to improve breathing, and stimulating the heartbeat.
Epinephrine designed for emergency home use comes in two forms: a traditional needle and syringe kit known as Ana-Kit, or an automatic injector system known as Epi-Pen. Epi-Pen's automatic injector design, originally developed for use by military personnel to deliver antidotes for nerve gas, is described by some as "a fat pen." The patient removes the safety cap and pushes the automatic injector tip against the outer thigh until the unit activates. The patient holds the "pen" in place for several seconds, then throws it away.
While Epi-Pen delivers one premeasured dosage, the Ana-Kit provides two doses. Which system a patient uses is a decision to be made by the doctor and patient, taking into account the doctor's assessment of the patient's individual needs.
Because there is no "cure" for food allergies other than strict avoidance of an offending food, one of the biggest problems those with food allergies face is verifying whether a forbidden product is contained in a particular food. For example, in Sampson's study, all six deaths occurred because either the child or the parent was unaware the food contained a substance to which the child was allergic. Munoz-Furlong says the Nutrition Labeling and Education Act, which requires more complete food labeling, should greatly help people with food allergies to avoid dangerous foods.
"The new labeling changes will make it easier for the consumer to readily identify things they could be allergic to," says Linda Tollefson, D.V.M., chief of the epidemiology branch at FDA's Center for Food Safety and Applied Nutrition. "Before this law was passed, true allergens were required to be on the label, but the exceptions were standardized foods, which will now have to list all ingredients."
According to Elizabeth J. Campbell, director of the center's division of programs and enforcement policy, the principle underlying standardized foods originally was that people basically knew what was in various foods.
"Originally, food standards were adopted to ensure uniformity. If you saw a product labeled mayonnaise, food standardization meant it had to be mayonnaise. People used to know what was in mayonnaise; nowadays they have to be told that mayonnaise contains both eggs and oil," Campbell says. "Years ago, when the law was first written to provide for standards of identity for certain foods, it only required that optional ingredients be declared. The new law stipulates that all ingredients in standardized foods must be declared." (See "Ingredient labeling: What's in a Food?" in the April 1993 FDA Consumer.)
Campbell believes that once the labeling is in place, consumers will have the information they need to make correct food choices. "In most cases, ingredients have to be labeled simply because they are ingredients, not because they are unsafe," she stresses. "For those with food allergies, I think it is more of a patient education problem."
Food additives, such as sulfites and certain colors, can also cause problems for people sensitive to them.
"If you have a food allergy, you really have to alter your life," Tollefson says. "You have to really read labels, and really be careful about what you eat."
Steve Taylor, Ph.D., a professor and head of Department of Food Science and Technology at the University of Nebraska in Lincoln, says the biggest problem for people with food allergies is restaurant food. Historically, restaurants have been regulated by local heath departments and have not had to label foods.
"For many restaurants, labeling of food products they serve would cause horrendous problems...what about chalkboard menus? How would you include all the ingredients? Enforcement would be a nightmare," he admits.
But steps are being taken to better educate restaurant employees. The Food Allergy Network and The American Academy of Allergy and Immunology, along with the National Restaurant Association, recently produced a pamphlet on food allergies, which has been distributed to 30,000 members of the association. The brochure explains what restaurants can do to help customers who need to avoid certain foods, defines anaphylaxis, and advises employees on what to do if food allergy incidents occur.
John A. Anderson, M.D., director of the Allergy and Immunology Training Program at Henry Ford Hospital in Detroit, says changes in food habits may be responsible for the feeling some physicians have that food allergies may be on the rise.
"You could make a case for the fact that we are introducing peanuts, in the form of peanut butter, to people at a very young age, which would affect the prevalence rate for people who are sensitive to that allergen," he notes. "In Japan, where they use more soy, there is a higher prevalence of soy allergy. My feeling is that as soy, a cheap protein supplement, is put in a lot of commercial foods you will see an increase in the rate sensitivity worldwide."
Metcalfe say that if food allergies are rising, it is due to more common use of foods that tend to be allergenic. He cites milk as a source of protein supplement in many prepared foods, and points out that people are eating more exotic seafood and more fish.
"But it's important to remember that the majority of people with true food allergies are allergic to three or fewer foods," Metcalfe says.
Other than advising anyone with a known or suspected severe food allergy to carry and know how to self-administer epinephrine, there is no treatment for food allergy other than to eliminate the offending food. But Metcalfe is optimistic about the future.
"I don't think it is likely a drug will be found to prevent food allergies. But I do think within 10 years we will see allergy shots available for some of the more common food allergies, because we are learning to identify and purify food allergens. I think we will see some development of immunotherapy for food allergies," he says.
What should you do if you suspect you have a food allergy?
The Food Allergy Network's Anne Munoz-Furlong suggests keeping a food diary as a first step, writing down everything you eat or drink for a one- or two-week period. Note any symptoms and how long it took for such symptoms to develop.
But Furlong and other experts agree that those who suspect food allergies also need to be evaluated by a physician with intensive specialty training in allergy and immunology. Be sure to discuss what diagnostic and treatment plan is anticipated, and the costs.
Ask if the tests have been proven effective by accepted standards of scientific evaluation.
"Go to a board-certified physician who is an allergy expert," advises Paul C. Turkeltaub, M.D., associate director of the division of allergenic products and parasitology at FDA's Center for Biologics Evaluation and Research. "Be very wary of claims of food allergy to explain chronic, common complaints."
The diagnosis of food allergy requires a careful history, physical exam, appropriate exclusion diet, and diagnostic test to rule out other conditions. Tests can include direct allergy skin tests, blood tests, or "elimination and challenge" tests for suspected foods.
The most accurate kind of test is a controlled challenge test, often done in "blind" or "double-blind" fashion to eliminate psychological factors. In a blind challenge, the patient is given either a sample of the food, without being told what it is, or a placebo, an inert substance used as a control in the test. The observer (a doctor or assistant), however, knows what the substance is. Both patient and observer record any symptoms of allergic reaction. In a double-blind challenge, neither the patient nor the observer knows if the patient is given the food (allergen) or the placebo.
In recent years, unproven tests such as "food cytotoxic blood tests" and "sublingual provocation food testing" have been promoted as supposed "diagnostic" tools to detect food allergies. FDA believes that food cytotoxic blood tests are not supported by well-controlled studies and clinical trials.
In food cytotoxic testing, a test tube of blood is taken from the patient. The white cells (leukocytes) are mixed with plasma and sterile water and placed on microscope slides coated with dried extracts of a particular food. The reaction of the cells is then examined under a microscope; if they change shape, disintegrate, or collapse--or the person examining them says they do--the patient is supposedly allergic to that particular food. Test results may be interpreted by a "nutritional counselor" working on commission, who recommends vitamins and minerals (often available on site) that the patient needs to correct his or her "allergic condition." But FDA and other experts emphasize there is no evidence that such tests are valid in diagnosing food allergies.
Sublingual provocation food testing dates back to 1944. The test consists of placing three drops of an allergenic extract under a patient's tongue and waiting 10 minutes for any symptoms to appear. When the doctor is satisfied he has determined the cause of the symptoms, he administers a "neutralizing" dose, which is usually three drops of a diluted solution of the same allergenic extract. The symptoms are then expected to disappear in the same sequence in which they appeared. Advocates claim that if the neutralizing dose is given before a challenge test (for instance, eating a meal containing the offending food), the person will not have symptoms.
But after careful study of existing data, The American Academy of Allergy and Immunology says no controlled clinical studies demonstrate either diagnostic or therapeutic effects of sublingual provocation food testing. The academy concludes that use of the tests should be reserved for experiments in well-designed trials.
If you are diagnosed with a food allergy, scrutinize food labels to detect potential sources food allergens. When eating out, ask about ingredients if you are unsure about a particular food; ask to talk to the manager of the restaurant about ingredients in specific dishes.
Keep epinephrine with you and know how to administer it. If you do experience a reaction, seek medical attention immediately, even if the symptoms are mild or seem to subside. Mild symptoms may be followed 10 to 60 minutes later by the onset of severe problems.