Date Published: November 10, 2011
Publisher: BioMed Central
Author(s): Susan Waserman, Wade Watson.
Food allergy is defined as an adverse immunologic response to a dietary protein. Food-related reactions are associated with a broad array of signs and symptoms that may involve many bodily systems including the skin, gastrointestinal and respiratory tracts, and cardiovascular system. Food allergy is a leading cause of anaphylaxis and, therefore, referral to an allergist for appropriate and timely diagnosis and treatment is imperative. Diagnosis involves a careful history and diagnostic tests, such as skin prick testing, serum-specific immunoglobulin E (IgE) testing and, if indicated, oral food challenges. Once the diagnosis of food allergy is confirmed, strict elimination of the offending food allergen from the diet is generally necessary. For patients with significant systemic symptoms, the treatment of choice is epinephrine administered by intramuscular injection into the lateral thigh. Although most children “outgrow” allergies to milk, egg, soy and wheat, allergies to peanut, tree nuts, fish and shellfish are often lifelong. This article provides an overview of the epidemiology, pathophysiology, diagnosis, management and prognosis of patients with food allergy.
In recent years, there has been a significant amount of media attention on the subject of food allergy. While the exact prevalence is unknown, recent estimates suggest that 6% of young children and up to 4% of adults in North America are affected by food allergy, and the prevalence of the disorder appears to be rising [1-4].
The term food allergy is used to describe an adverse immunologic response to a food protein. It is important to distinguish food allergy from other non-immune-mediated adverse reactions to foods, particularly since more than 20% of adults and children alter their diets due to perceived food allergy . Adverse reactions that are not classified as food allergy include food intolerances secondary to metabolic disorders (e.g., lactose intolerance), reactions to toxic contaminants (e.g. histamine produced by scombroid fish contaminated by Salmonella organisms) or pharmacologically active food components (e.g. caffeine in coffee causing jitteriness, tyramine in aged cheeses triggering migraine). Other conditions which are associated with symptoms similar to food allergy include auriculotemporal syndrome (a disorder characterized by facial flushing and salivation that may follow trauma to the parotid gland), and gustatory rhinitis [2-4].
Although food allergy can arise to any food, the allergens responsible for more than 85% of food allergy are: milk, egg, peanut, tree nuts, shellfish, fish, wheat, sesame seed and soy . These are also the “priority” allergens defined by Health Canada. It is the protein component, not the fat or carbohydrate component, of these foods that leads to sensitization and allergy. The allergenic segments or “epitopes” of these proteins tend to be small (10 to 70 kd in size), water-soluble glycoproteins that are generally resistant to denaturation by heat or acid and, therefore, can remain intact even after processing, storage, cooking and digestion [3,4,6]. Examples of these glycoproteins include caseins in milk, vicillins in peanut, and ovomucoid in egg. In general, allergies to additives and preservatives are uncommon.
Many food allergies, particularly allergies to milk, egg, soy, and wheat, are usually outgrown within the first ten years of life . In contrast, allergies to peanut, tree nuts, fish, and shellfish are often lifelong, although 20% of individuals may outgrow peanut allergy . Peanut and tree nuts are responsible for the most serious allergic reactions and food-allergy related fatalities . Canadian prevalence estimates for five of the major food allergens (i.e., peanut, tree nuts, fish, shellfish, and sesame) are shown in Table 1.
Food allergy is associated with a broad array of well-defined signs and symptoms, and can involve many body systems including the skin, GI and respiratory tracts, and cardiovascular system (see Table 2). Food allergy is not felt to play a role in chronic respiratory symptoms.
The diagnosis of a food allergy requires a detailed history and physical examination, and diagnostic tests, such as skin prick tests (SPT) and/or serum-specific IgE testing to foods (ImmunoCAP®). In some cases, oral food challenges may also be required [2-4].
There is currently no treatment for food allergy, beyond avoidance of the responsible food(s). Once a food allergy is diagnosed, strict elimination of the offending food allergen from the diet is necessary. A properly managed, well-balanced elimination diet can lead to resolution of symptoms while maintaining nutritional status. When the elimination diet is used as treatment, the identified food allergens are removed from the diet indefinitely, unless evidence exists that the food allergy has resolved [2-4].
Strategies for the prevention of food allergy have been extensively studied. Prior recommendations suggesting avoidance of highly allergenic foods in infant diets and the diets of pregnant/breastfeeding mothers have not been shown to decrease the prevalence of food allergy or atopic disease . Recent guidelines from the American Academy of Pediatrics state that “no current convincing evidence exists to recommend specific avoidance of certain foods beyond 4-6 months of age for the prevention of allergy” .
The prognosis of food allergy is complex and dependent on the particular food. As mentioned earlier, most infants and young children outgrow allergies to milk, egg, soy and wheat. Children should be re-evaluated at regular intervals to determine whether clinical tolerance has developed. The natural history of egg and milk allergy appears to be evolving in that an increasing number of children are outgrowing these allergies in their teenaged years [23,24]. Allergy to peanut, tree nuts, fish, and shellfish is more persistent, and lifelong in most cases.
Food allergy is an important clinical problem of increasing prevalence. Assessment by an allergist is very important for appropriate diagnosis and treatment. Diagnosis currently relies on a careful history and diagnostic tests, such as SPT, serum-specific IgE testing (where appropriate) and, if indicated, oral food challenges. The mainstay of treatment is avoidance of the responsible food(s) and appropriate, prompt response to allergic reactions with epinephrine. Further insights into the pathophysiology of food allergy will lead to the development of improved methods for prevention, diagnosis, and management of the disorder.
Dr. Susan Waserman has received consulting fees and honoraria from AstraZeneca, GlaxoSmithKline, King Pharma, Merck, Novartis, Nycomed, and Paladin.