Dictionary of Allergies .. Food allergy

The term ''food allergy'' is widely misused for all sorts of symptoms and diseases caused by food. Food allergy (FA) is an adverse reaction to food (food hypersensitivity) occurring in susceptible individuals, which is mediated by a classical immune mechanism specific for the food itself.

The best established mechanism in FA is due to the presence of IgE antibodies against the offending food. Food intolerance (FI) are all non-immune-mediated adverse reactions to food. The subgroups of FI are enzymatic (e.g. lactose intolerance due to lactase deficiency), pharmacological (reactions against biogenic amines, histamine intolerance), and undefined food intolerance (e.g. against some food additives). The diagnosis of an IgE-mediated FA is made by a carefully taken case history, supported by the demonstration of an IgE sensitization either by skin prick tests or by in vitro tests, and confirmed by positive oral provocation. For scientific purposes the only accepted test for the confirmation of FA/FI is a properly performed double-blind, placebo-controlled food challenge (DBPCFC)[1]. Intradermal testing has a higher false-positive rate and greater risk of adverse reactions; therefore, it should not be used for initial evaluations[2].A panel of recombinant allergens, produced as single allergenic molecules, may in future improve the diagnosis of IgE-mediated FA. Due to a lack of causal treatment possibilities, the elimination of the culprit <<food allergen>> from the diet is the only therapeutic option for patients with real food allergy[1].

Family physicians play a central role in the suspicion and diagnosis of immunoglobulin E-mediated food allergies, but they are also critical in redirecting the evaluation for symptoms that patients are falsely attributing to allergies. Although any food is a potential allergen, more than 90 percent of acute systemic reactions to food in children are from eggs, milk, soy, wheat, or peanuts, and in adults are from crustaceans, tree nuts, peanuts, or fish. The oral allergy syndrome is more common than anaphylactic reactions to food, but symptoms are transient and limited to the mouth and throat. Skin-prick and radioallergosorbent tests for particular foods have about an 85 percent sensitivity and 30 to 60 percent specificity[2]. Treatment is through recognition and avoidance of the responsible food. Patients with anaphylactic reactions need emergent epinephrine and instruction in self-administration in the event of inadvertent exposure. Antihistamines can be used for more minor reactions[2]. Current therapeutic approaches to food allergy are focused on modulating the immunologic response to food proteins to promote induction of oral tolerance[3].

The inability to accurately predict the severity of future allergic reactions to foods in a given individual coupled with the real--although usually remote--risk of a fatal anaphylactic reaction complicates care and remains a constant source of concern to food-allergic patients, their family members, and health care providers. Current epidemiologic evidence suggests that the incidence of food-induced anaphylaxis is increasing, although confidently approximating the incidence of fatal allergic reactions to foods remains difficult. 

References

1. Wüthrich B. Food allergy, food intolerance or functional disorder? Praxis (Bern 1994). 2009 Apr 1;98(7):375-87

2. Kurowski K, Boxer RW. Food allergies: detection and management. Am Fam Physician. 2008 Jun 15;77(12):1678-86. Summary for patients in: Am Fam Physician. 2008 Jun 15;77(12):1687-8.

3. Scurlock AM, Burks AW, Jones SM. Oral immunotherapy for food allergy. Curr Allergy Asthma Rep. 2009 May;9(3):186-93.

4. Atkins D, Bock SA. Fatal anaphylaxis to foods: epidemiology, recognition, and prevention. Curr Allergy Asthma Rep. 2009 May;9(3):179-85.