Food represents the largest antigenic challenge confronting the human immune system. Food allergies are illnesses that affect only part of the population. True food allergies involve abnormal immunologic responses to food-borne substances. With true food allergy, even minute amounts of the offending food can cause potentially life-threatening reactions.
Two types of true food allergies occur: antibody-mediated and cell-mediated (Sampson, 1994). Allergens are typically naturally occurring proteins from the implicated food. Those proteins that are resistant to digestion can elicit the formation of antibodies, but only the formation of allergen-specific immunoglobulin E (IgE) elicits allergic sensitization.
The antibody-mediated allergies (also known as atopy or immediate hypersensitivity) occur immediately after consumption of the offending food. The foods most commonly involved in IgE-mediated food allergies are peanuts, cow milk, eggs, soybeans, nuts from trees, wheat, and seafood.
The sole known example of a cell-mediated food allergy is celiac disease, also known as gluten-sensitive enteropathy. This is a delayed hypersensitivity reaction because the onset time between ingestion of the offending food and development of symptoms can be from 24 to 72 hours later. Signs and symptoms of celiac disease result from the ingestion of the gluten protein fraction of wheat, rye, barley, triticale, and oats.
The prevalence of IgE-mediated food allergies in the population is estimated to be between 4 and 8 percent of young infants, 1 and 2 percent of children, and less than 1 percent of adults (Sloan and Powers, 1986). The prevalence of celiac disease has been estimated at 1 in every 3,000 individuals in the United States (Ekvall, 1993). The prevalence of food allergies among the WIC population was not available to the committee.
Atopic diseases such as asthma, allergic rhinitis, and atopic dermatitis can all be precipitated by antigenic foods. Both upper and lower respiratory symptoms have been demonstrated as a result of food allergy; however, the role of nutrition part from avoidance of the allergenic food could not be documented.