Food Allergy

by Donald Y.M. Leung, M.D., Ph.D. & Allan Bock, M.D.

Print PDF Version

Allergy vs. Adverse Reaction ... Incidence ... Patterns & Character of Hypersensitivity ... Age of Onset ... Recognition & Diagnosis ... Treatment ... References

See also Peanut Allergy

Allergy vs. Adverse Reaction

Food reactions are real and not uncommon; however, true food allergy is probably rarer than generally thought. Part of the confusion results from failure to distinguish immune-mediated (IgE or allergic) reactions from other adverse reactions to food. ² The latter can be caused by intestinal enzyme deficiencies, microbial toxins or infections, neurologic or psychological reactions and reactions to noxious natural constituents of foods. ³ Therefore, an adverse reaction or food intolerance is not necessarily a food allergy, i.e., an immunologic (IgE) mediated reaction.

Incidence

Many patients report they suffer from food allergy. Estimates for adults believing they are allergic to certain foods go as high as 30%. ⁴ But for most of these, no allergy is found when their history is tested against a double-blind, placebo-controlled food challenge--the most objective, scientific standard. The prevalence of IgE-mediated food allergy or food hypersensitivity is estimated to range from 0.1% to 7% in the population. ³ Patients who truly are allergic generally find it's not to nearly as many foods as they think.

Patterns & Character of Hypersensitivity

A 1990 report by Bock and Atkins ⁵ on patterns of food hypersensitivity during 16 years of study found that 39% of 480 children with a history of food allergy had positive Double-Blind-Placebo-Controlled Food Challenge (DBPCFC) results. The investigators concluded that food hypersensitivity (food proteins producing immunologically mediated reactions) does exist, but it does not involve as many foods as usually suspected and is often over reported. Of the food reactions objectively confirmed in this study, 95% were to egg, peanut, milk, soy, fish, wheat and tree nuts. Multiple food hypersensitivity and placebo reactions were rare findings.

In a study of 160 children with severe eczema, 80% of the subjects diagnosed with food hypersensitivity reacted to only one or two foods. Also, allergy to foods was highly specific; only one patient reacted to more than one food within a botanical family or animal species. ²

Virtually any food, as well as food additives, can cause allergic reactions; however, true allergy to two commonly suspected foods - chocolate and corn-- rarely exists. The prevalence of reactions to specific foods depends, in part, on the eating habits of a given population; for example, fish allergies appear to be more prevalent in Scandinavian countries, whereas soybean allergy is more common in Japan.

People who are allergic to milk and soy products usually have a less severe reaction and usually outgrow their sensitivity. People allergic to peanuts and shrimp, on the other hand, often have a severe reaction, even anaphylaxis causing death, and usually don't outgrow their allergy.

Age of Onset

Food allergy occurs most frequently in children from birth to age of 3 years, and most of that in the first year of life. ⁶ After age 3, most children have outgrown these reactions. The notable exception is allergies to peanut and tree nuts, which generally are life-long conditions. The occurrence of food allergy in adults has been well documented, but, in one longitudinal study, the patterns of symptoms, foods causing reactions and natural history were similar to the findings in children. ¹¹

Recognition & Diagnosis

Clinical manifestations of food allergy include classic respiratory, skin and gastrointestinal allergic symptoms, such as systemic anaphylaxis, asthma, allergic rhinitis, atopic dermatitis, dermatitis herpetiformis, gluten, milk and soy enteropathies and eosinophilic gastroenteritis, urticaria, angioedema, vomiting, diarrhea and abdominal pain. ^2,3

Allergic reactions to food typically involve immediate or quick onset of symptoms. Delayed reactions several hours or days later have been reported, but have rarely been verified in blind challenges.

Diagnosing food allergy usually requires a through review of the patient's history, physical examination, skin testing, food elimination and oral challenge. Although skin testing is not always definitive in predicting allergic symptoms, it is a useful method to determine immediate hypersensitivity.

Treatment

After identifying a food that may be causing allergy and confirming your suspicion with a double-blind food challenge, the available therapy is: avoid the allergen, i.e. eliminate it from the diet. Allergy must be determined to each food separately, rather than assuming that allergy to a whole food group.

During infancy, avoidance is best accomplished by breast feeding, with the mother also avoiding the allergen and other highly allergenic food. Patients using food elimination as an allergy treatment must be careful to partake of a balanced and nourishing diet.

It is typical for patient with food Hypersensitivity, especially those under age 3, to lose or "outgrow" their symptomatic reaction, possibly through development of immunologic tolerance. That is why an offending food which has been eliminated from the diet should be reintroduced cautiously and gradually to see if it can be tolerated. These regular interval challenges must be carefully controlled, using very small amounts of the food and gradually increasing the challenge. ⁶

In this instance, the physician should adequately prepared to treat anaphylaxis and patients with proven anaphylaxis, especially older children and adults, should not be rechallenged. ³

Total avoidance is difficult for most people, since eggs, peanuts, tree nuts and milk are common ingredients in many foods. However, this therapy can be accomplished safely and effectively if the patient does not have multiple food allergies and/or severe anaphylactic reaction to a minute quantity of the allergen. Carefully reading food labels and being alert for food that commonly contain the offending substance is recommended.

Food allergies an be very significant for some patients, occasionally resulting in death, and should not be treated cavalierly. However, with careful, accurate diagnosis, the majority of patients can identify and remedy their problem with reasonable measures.

For people susceptible to anaphylaxis it is imperative to carry an epinephrine kit at all times and a medical emergency information bracelet in case accidental exposure to an allergen brings on anaphylaxis. Review of fatal food-induced anaphylaxis by Yunginger et al. ¹⁰ reveals that delayed administration of such remedies was a common factor.

References (Updated, July, 2002)

1. Bock SA. Food Allergy: a primer for people. Denver: A.J. Publishing, 1982.

2. Lemanske RF, Jr., Sampson HA. Adverse reactions to foods and their relationship to skin diseases in children. Adv Pediatr 1988;35:189-218. UI: 3055858.

3. Kettelhut BV, Metcalfe DD. Adverse Reactions to Foods in "Allergy: Principles and Practice. In: Middleton E, Reed CE, Ellis EF, Ad!dnson NF, Yunginger JW, eds. Allergy: Principles and Practice. 3rd ed. St. Louis: CV Mosby Co, 1988:1481-1502.

4. Kocoshis SA. Pharmacotherapy of Childhood Food Allergies. Amer J Asthma Allergy Pediatr 1991;4(4):184-8.

5. Bock SA, Atkins FM. Patterns of food hypersensitivity during sixteen years of double-blind, placebo-controlled food challenges. J Pediatr 1990;117(4):561-7. UI: 2213379.

6. Bock SA. Prospective appraisal of complaints of adverse reactions to foods in children during the first 3 years of life. Pediatrics 1987;79(5):683-8. UI: 3575022.

7. Sampson HA. Peanut anaphylaxis. J Allergy Clin Immunol 1990;86(1):1-3. UI: 2196300.

8. Sachs MI, Yunginger JW. Food-Induced Anaphylaxis. Immun Allergy Clin No Amer 1991;11(4):743-55.

9. Leung DY, Rhodes AR, Geha RS. AtopicDermatitis. In: Fitzpatrick TB, Eisen AZ, Wolff K, Fredberg IM, Aristen KF, eds. Dermatology in General Medicine. 3rd ed. New York: McGraw-Hill, 1986:1385-1408.

10. Yunginger JW, Sweeney KG, Sturner WQ, et al. Fatal food-induced anaphylaxis. JAMA 1988;260(10):1450-2. UI: 3404604.

11. Pastorello EA, Stocchi L, Pravettoni V, et al. Role of the elimination diet in adults with food allergy. J Allergy Clin Immunol 1989;84(4 Pt 1):475-83. UI: 2794292.

The Medical Scientific Update, a publication of the Office of Professional Education at National Jewish, provides information to physicians about our clinical and research programs in allergic, respiratory, and immune system disorders. The Web edition of the Medical Scientific Update published by the Gerald Tucker Memorial Medical Library.