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Advice from your Allergist

Here's some food for thought.

Allergies, including hay fever, asthma and skin disorders, affect 58.7 million Americans or 25% of the population. Although the true incidence of food allergy is unknown, a recent study suggests that about 5% of the population may suffer from adverse reactions to food.

Historical records show that people have long been ware of food allergy. Hippocrates noted that cow's milk could cause gastric upset and hives. The Roman poet Lucretius said, "One man's meat is another man's, poison." And some scholars believe Old Testament dietary restrictions were based upon the awareness that certain foods could cause adverse reactions. However, the serious study of food allergy began at the start of this century. Since then, research has led to effective procedures for the diagnosis and treatment of food allergy, relieving the symptoms of millions with this problem.

What are some common symptoms of food allergy?
Vomiting, nausea, stomach cramps, indigestion, diarrhea, hives, eczema, headaches, asthma, earaches and rhinitis (itchy, stuffy, runny nose; sneezing, and phlegm in the throat) are among the most common symptoms. In fact, many parts of the body can be affected by food allergy. The frequency and severity of symptoms vary widely from one person to another. Highly allergic persons may experience severe and life threatening reactions such as upper airway swelling of the tongue and lips while, in milder cases, others may only suffer a minor case of sniffles. Because these symptoms can be caused by a number of diseases, your allergist may want to examine you to rule them out as the source of your problem. Not all adverse reactions to foods are due to allergy. Some reactions to milk, for example, are related to a deficiency of an enzyme (lactase) which normally breaks down a sugar in milk (i.e. lactose). This deficiency in some individuals causes a reaction similar to food allergy when milk is ingested.

What causes my symptoms?
Allergy is caused when your body's immune system over-reacts to the introduction of offending substances. Normally, your body's defense mechanisms (antibodies) keep you healthy by fighting such invaders as bacteria and viruses, which can cause infections, and inactivating allergens, which ran cause allergic reactions. The body produces several types of antibodies, or immunoglobulins. When antibodies battle with allergens, chemicals, including histamine, are released as a part of the body's reaction to these substances. One anti-body in particular, immunoglobulin E or IgE for short is produced in greater quantities than normal by persons with allergies. In large amounts, IgE released chemicals can cause blood vessels to widen, smooth muscles to contract and affected skin areas to become red, itchy and swollen, resulting in an allergic reaction. In fact, these IgE antibodies found in tissues and secretions are thought to be responsible for classic allergy symptoms such as hives, swollen nasal membranes, diarrhea and wheezing.

Why me? Why have I developed food allergy?
You probably inherited it. Heredity seems to be the prime reason some people have allergies and others don't. If both your parents have allergies, you have a 75117c chance of being allergic. If one parent is allergic or you have relative on one side with allergies you have a 5017c chance of becoming allergic. Although food allergy occurs most often in infants and children, it can appear at any age and can be caused by foods that have been eaten for years without any problems.

Other factors also come into play. For instance, excessive exposure to a particular food may create sensitivity to that food as testified to by the high incidence of fish allergy among Scandinavians and of rice allergy among the Japanese.

Some foods are more potent allergens than others. More people suffer reactions from peas than from carrots, from citrus fruits than from pears. Also, your reaction to a particular food can be affected by your physical condition at the time. If you have a cold, an upset stomach or a non-food allergy hay fever, for example, during high pollen season you may be more susceptible to food allergy. Emotional stress also may aggravate allergic symptoms.

What foods are most likely to cause allergy?
Eggs, milk, nuts, soy, seafood, fish, corn and wheat are the most common allergy causing foods, but almost any food can cause allergy. Keep in mind that if you are allergic to a particular food, you might be allergic to related foods. For example, a person allergic to avocado also may react to bay leaves because they're in the same botanical family. Likewise, a person allergic to peanuts often cannot tolerate other members of the legume family whose members include peas, beans and licorice.

How do allergists determine which foods make me sick?
The procedure varies from patient to patient. Some persons know exactly what food causes their allergies. They eat strawberries and immediately break out with hives, or they drink milk and immediately begin vomiting or get diarrhea. Sometimes, however, they need their allergist's help in determining the "culprit," especially when symptoms show up man hours after ingesting an offending food.

Your allergist may begin by taking a detailed history. He'll look for clues in your lifestyle that will help pinpoint the cause of your problem. You'll be asked about your work and home environments, your eating habits, your family's medical history and miscellaneous matters, such as what kind of heating and cooking fuels you use, and if you have pets.

But some of these questions don't have anything to do with food!

These questions are necessary because your allergist wants to eliminate the possibility that another problem or multiple allergies may be causing your symptoms. For example, a patient's allergy to pollen or mold may trigger his allergy to eggs, so that in the summer, when mold and pollen are everywhere he may not be able to eat eggs even though he can eat them safely the rest of the year.

What's next, after taking history?
You may require some tests. Your allergist may employ skin testing, in which small amounts of the suspected allergen are introduced into the skin. A positive reaction a wheal, swelling or flare in the surrounding red area indicates the presence of allergic antibodies. Some patients are given RAST tests, which use blood samples to determine the extent of antibody product against an allergen.

Will these allergy tests pinpoint my problem?
Although these tests give your allergist further clues for the diagnostics, they are not 100% reliable. With the information gained from your history, physical exam and the tests, your allergist may further narrow down the suspected foods by placing you on a special diet.

If your symptoms occur only occasionally, the culprit is a food that is eaten infrequently. Your allergist may ask you to keep a daily food diary listing all food and medication ingested, along with your symptoms for the day. By comparing "good days" with "bad days," you and your allergist can determine which foods are prime suspects.

Then you may be asked to follow a trial diet, which alternates days of consumption and avoidance of suspected foods. If your symptoms subside during abstinence - and flare up when you eat the food again - the problem food has been identified.

But I have allergy symptoms every day. How do my allergist and I begin to identify what foods I'm allergic to?
Your allergist may ask you to go on an elimination diet tailor made for you. You may be asked to eliminate foods implicated on the basis of your history, foods known to be highly allergenic and foods indicated in positive skin tests. After several weeks on the elimination diet, your system should be cleared of allergenic foods. When your symptoms cease, your allergist may reintroduce foods one at a time to your diet, and watch for reactions.

This reintroduction is called a "challenge." Many challenges may be necessary to identify which foods are safe for you and which will make you sorry. In some cases, not all offending foods or additives can be identified. Then your allergist may prescribe drugs to ease the symptoms.

Once my allergy is identified, how is it treated?
Avoidance of the allergenic food is the best policy. You must be vigilant in checking ingredient labels of food products to make sure an offending food or food additive is not present. For example, a person allergic to milk must avoid ice cream, cheese, chocolate bars, many cake mixes, and luncheon meats in which milk is used as filler. If you are allergic to fish, be aware that glue on envelopes sometimes is made with fish products and could cause an allergic reaction. Special food allergy cookbooks are widely available. Your allergist can recommend some to you.

Will I ever be able to eat these foods again?
If you have a severe immediate type reaction to certain foods, NEVER taste them again. In some very sensitive persons a small taste of an allergenic food can produce a life threatening reaction. However, if your symptoms are milder, you may be able to try a problem food again. After you have abstained of at least six months or longer, your allergist may suggest that you try a small portion of a problem food. If you have no reaction, you may be able to eat this food occasionally and in moderation. Allergic reactions to foods have been known to disappear for months or years then reappear. In some cases, the allergy disappears for good.

If you use caution and carefully follow your allergist's advice, you can bring your food allergy under control. If you have more questions, consult your doctor.

Source: Palo Alto Medical Foundation

Adapted by Editorial Staff, June 2007
Last update, August 2008