Food Allergies Rare But Risky
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.
Allergy and Intolerance: Different Problems
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.
When Food Additives are a Problem
Over the years, people have reported to FDA adverse reactions to certain food additives, including aspartame (a sweetener), monosodium glutamate (a flavor enhancer), sulfur-based preservatives, and tartrazine, also known as FD&C Yellow No. 5 (a food color). The federal Food, Drug, and Cosmetic Act requires that FDA ensure the safety of all substances added to foods, but individual health conditions sometimes cause problems with certain additives.
After reviewing scientific studies, FDA determined in 1981 that aspartame was safe for use in foods. In 1987, the General Accounting Office investigated the process surrounding FDA's approval of aspartame and confirmed the agency had acted properly. However, FDA has continued to review complaints alleging adverse reactions to products containing aspartame. To date, FDA has not determined any consistent pattern of symptoms that can be attributed to the use of aspartame, nor is the agency aware of any recent studies that clearly show safety problems.
Carefully controlled clinical studies show that aspartame is not an allergen. However, certain people with the genetic disease phenylketonuria (PKU), those with advanced liver disease, and pregnant women with hyperphenylalanine (high levels of phenylalanine in blood) have a problem with aspartame because they do not effectively metabolize the amino acid phenylalanine, one of aspartame's components. High levels of this amino acid in body fluids can cause brain damage. Therefore, FDA has ruled that all products containing aspartame must include a warning to phenylketonurics that the sweetener contains phenylalanine.
Monosodium glutamate (MSG) has been used for many years in home and restaurant foods, and in processed foods. People sensitive to MSG may have mild and transitory reactions when they eat foods that contain large amounts of MSG (such as would be found in heavily flavor-enhanced foods). Because MSG is commonly used in Chinese cuisine, these reactions were initially referred to as "Chinese restaurant syndrome."
FDA believes that MSG is a safe food ingredient for the general population. It is regarded by the agency as among food ingredients that are "generally recognized as safe." FDA has studied adverse reaction reports and other data concerning MSG's safety. The agency also has an ongoing contract with the Federation of American Societies for Experimental Biology to re- examine the scientific data on possible adverse reactions to glutamate in general. MSG must be declared on the label of any food to which it is added.
Of all the food additives for which FDA has received adverse reaction reports, the ones that most closely resemble true allergens are sulfur-based preservatives. Sulfites are used primarily as antioxidants to prevent or reduce discoloration of light-colored fruits and vegetables, such as dried apples and potatoes, and to inhibit the growth of microorganisms in fermented foods such as wine.
Though most people don't have a problem with sulfites, they are a hazard of unpredictable severity to people, particularly asthmatics, who are sensitive to these substances. FDA uses the term "allergic-type responses" to describe the range of symptoms suffered by these individuals after eating sulfite-treated foods. Responses range from mild to life-threatening.
FDA's sulfite specialists say scientists, at this time, are not sure how the body reacts to sulfites. To help sulfite-sensitive people avoid problems, FDA requires the presence of sulfites in processed foods to be declared on the label, and prohibits the use of sulfites on fresh produce intended to be sold or served raw to consumers (see "A Fresh Look at Food Preservative" in the October 1993 FDA Consumer).
FD&C Yellow No. 5
Color additives must go through the same safety approval process as food additives. But one color, FD&C Yellow No. 5 (listed as tartrazine on medicine labels), may prompt itching or hives in a small number of people.
Since 1980 (for drugs taken orally) and 1981 (for foods), FDA has required all products containing Yellow No. 5 to list it on the labels so sensitive consumers could avoid it. (As of May 8, 1993, food labels must list all certified colors as part of the requirements of the Nutrition Labeling and Education Act of 1990. See "From Shampoo to Cereal, Seeing to the Safety of Color Additives" in the December 1993 FDA Consumer.)
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.
How to Cope
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.
Source: Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration.