The term "food allergy" is both an inappropriately and excessively used term by consumers and health professionals alike. Many call any adverse reaction to food an allergy, even when the underlying mechanism is unknown. The following glossary describes the proper terminology of food reactions:

What is a food allergy?

A true food allergy or food hypersensitivity is an adverse reaction to a food or food component that involves the body's immune system. Using milk as an example, an immunologic response would be cow's milk protein allergy, whereas the nonimmunologic response would be lactose intolerance, due to lactase deficiency. Although many people believe they have a food allergy, true food allergies are rare, affecting 1-3% of children under 6 years and less than 2% of adults in the general population.

The most common form of allergy is the Type I allergy which involves IgE antibody and release of chemical mediators, such as histamine, in response to ingestion of the offending allergen. Most allergens are glycoproteins that the immune system recognizes as foreign and tries to eliminate.

What are the most common food allergens?While any food protein is potentially capable of eliciting an allergic reaction, most reactions are due to a limited number of foods. The 'big five' - egg, milk, peanut, soy and wheat - account for ~ 85% of food allergies. If you add fish and tree nuts to that list you have now identified the cause of 95% of reactions.

What are the symptoms of an allergic reaction to food?

Responses can be quite variable from individual to individual. It may involve gastrointestinal reactions including nausea, abdominal cramps, vomiting and diarrhea, itchy rash, hives, asthma and hay fever, swelling of the lips, tongue and throat, migraine headaches and, in severe cases, anaphylaxis. Some cases of food-induced hives or anaphylaxis are dependent on a cofactor for exacerbation of clinical symptoms. The only cofactor clearly demonstrated to provoke symptoms is exercise.

Mood swings, attention problems or behavioral disorders are not allergic responses to the food you eat. Reactions to chemicals contained in foods, such as caffeine, that stimulate the central nervous system are well known, and clearly distinct from the allergy-mediated response described above.

How is a food allergy diagnosed?

Before one should embark on an investigation of a food allergy, there must be a reasonable suspicion of food sensitivity based on the development of symptoms following the consumption of a particular food. Random testing for food allergies without one of the symptoms listed above is likely to be futile and an unnecessary medical expense. If there is a reasonable suspicion of food allergy, the first step is allergy skin testing to the suspected foods. A negative skin test result is highly accurate and can be used to reassure you that you are not allergic. On the other hand, a positive test does not confirm an allergy, but suggests that you may be allergic to the particular food. Foods to which a positive test is obtained should be eliminated from your diet for a trial period to see whether your symptoms resolve.

The only completely objective test for validating a food allergy is the double-blind placebo-controlled food challenge. In this test, both the physician and patient are blinded to whether the testing substance contains placebo or food. Subjects ingest either placebo or food, and then symptoms are noted for a certain period of time. These day-long testing sessions are normally only conducted at academic medical institutions.

Accurate diagnosis of food allergy is important for several reasons. Deleting suspected foods from your diet has nutritional and social implications. If a major food group is avoided, then nutritional adequacy has to be ensured.

What is the treatment for food allergies?