Adverse reactions to foods may result from immunologic (food allergy) and nonimmunologic responses.^1,2 Food allergy is defined as an "adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food."¹ Food allergy affects approximately 8% of children in the United States, although rates of parent-perceived allergies are significantly higher.^3,4 It is not clear whether the discordance of self-perceived allergy compared with true allergy is the result of lay perceptions regarding any adverse response to a food being an "allergy," or simply incorrect self-diagnosis, but the discordance indicates the need for a physician diagnosis to avoid unnecessary dietary avoidance. Food allergies can be severe and potentially fatal, also indicating the need for careful diagnostic assessments and appropriate education regarding allergen avoidance and treatment of reactions.

There are a number of adverse reactions to foods that are not allergies. Toxins or pharmacologically active components of the diet account for several nonimmune adverse reactions, such as food poisoning. Food intolerance is another adverse reaction not involving the immune system. A common example is lactose intolerance caused by lactase insufficiency. Symptoms include abdominal discomfort, bloating, and loose stools from a reduced ability to digest lactose. Examples of adverse reactions to foods are shown in Table 31.1. This chapter focuses on food allergies. Although celiac disease involves an immune response to gluten, it is not generally considered among food allergies and is not discussed in this chapter (see Chapter 38: Nutrition in Management of Chronic Autoimmune Inflammatory Bowel Disease in Children).