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Food allergy is a common problem in the pediatric age group, one that has numerous manifestations and touches on many organ systems. As such, food allergy is often first seen and managed by the generalist such as the pediatrician or family practitioner. However, various aspects of food allergy may also necessitate the involvement of a subspecialist. For the purposes of this chapter, we will focus on the aspects of food allergy and intolerance that involve the gastrointestinal tract and may require the assistance of a gastroenterologist.

Immune-mediated food reactions are typical (IgE-mediated or type 1) food allergy as well as several types of food reactions that involve either mixed (IgE and non-IgE) or delayed (non-IgE) hypersensitivity. GI manifestations of type 1 food allergy include the oral allergy syndrome (OAS) and immediate hypersensitivity reactions. From this point forward, the term food allergy will refer to immune-mediated food reactions, with a particular emphasis on the gastrointestinal manifestations of each of these reactions.

Type I (IgE-mediated) immediate hypersensitivity reactions to foods are most common in young children, with 50% of these reactions occurring in the first year of life. The majority are reactions to cow’s milk or to soy protein from infant formulas.1 Other food allergies begin to predominate in older children, including egg, fish, peanut, and wheat. Together with milk and soy, these account for more than 90% of food allergy in children.2

There are several gastrointestinal illnesses that manifest as a result of mixed and non-IgE allergies. Some, such as gastroesophageal reflux (GER), infantile colic, constipation, and diarrhea, are multifactorial illnesses, in which food allergy may play a prominent role in a proportion of patients with refractory symptoms. Others, such as infantile allergic proctocolitis (AP), eosinophilic esophagitis (EoE), and in some cases eosinophilic gastroenteritis (EoG), are disorders where food allergy has been demonstrated as the main (if not only) causative factor.

The gastrointestinal tract plays a major role in the development of oral tolerance to foods. Through the process of endocytosis by the enterocyte, food antigens are generally degraded into non-antigenic proteins.3,4 Although the gastrointestinal tract serves as an efficient barrier to ingested food antigens, this barrier may not be mature for the first few months of life.5 As a result, ingested antigens may have an increased propensity for being presented intact to the immune system. These intact antigens have the potential for stimulating the immune system, and driving an inappropriate response directed at the gastrointestinal tract.

With IgE-mediated food allergy, the rapid onset of GI symptoms after food ingestion correlates highly with positive IgE–RAST or skin prick tests to the offending antigen, demonstrating that these reactions are related to typical type 1 hypersensitivity. On the other hand, in patients with OAS, symptoms relate to cross-reaction between similar epitopes on certain pollens and certain fruits and vegatables.6

EoE and gastroenteritis are thought to ...

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