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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.
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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.
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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
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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.
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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.
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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
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EoE and gastroenteritis are thought to ...