Food Allergies
Mitchell R. Lester
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Abbreviations Used
AD: Atopic dermatitis
CD: Celiac disease
DBPCFC: Double-blind, placebo-controlled food challenge
EoE: Eosinophilic esophagitis
EGID: Eosinophilic gastrointestinal disorder
FA: Food allergy
FPIES: Food protein-induced enterocolitis syndrome
GER: Gastroesophageal reflux
NPV: Negative predictive value
PPV: Positive predictive value
RAST: Radioallergosorbent test

Food allergy (FA) is an adverse reaction to food arising from a specific immune response that occurs reproducibly upon re-exposure. Many patients assume food allergies are limited to IgE-mediated (immediate hypersensitivity) reactions. Although immediate reactions are most common, most frightening, and most publicized, other food allergies are not IgE- mediated or have mixed IgE/non-IgE mechanisms (Table 1). It is important to identify the specific mechanism whenever possible and to avoid using vague terms such as “food sensitivity” and “food intolerance”.

Non-immunologic adverse reactions to food are probably more common than allergic reactions (Table 2). Furthermore, patients with external locus of control often blame food for conditions that are not attributable to specific foods.

Table 1: Immunologic adverse reactions to food (food allergies)

IgE-Mediated

Mixed IgE/Non-IgE Mediated

Non-IgE Mediated

Urticaria/angioedema

Atopic dermatitis

Food-protein induced enterocolitis syndrome

Immediate gastrointestinal allergy

Eosinophilic esophagitis

Food-protein induced enteropathy

Anaphylaxis

Eosinophilic gastritis

Allergic/eosinophilic proctocolitis

Contact urticaria

Eosinophilic gastroenteritis

Celiac Disease/dermatitis herpetiformis

Food-pollen syndrome

Eosinophilic enteritis

Heiner’s Syndrome

Fruit-Latex Syndrome

 

Contact dermatitis

Asthma/rhinitis

 

 



Table 2: Non-allergic adverse reactions to foods.

Toxic/pharmacologic

Non-toxic/intolerance

Disorders not related to specific foods

Bacterial food poisoning

Lactase deficiency

Migraine headache (some)

Heavy metal poisoning

Fructose intolerance

Behavioral problems

Scombroid poisoning

Galactosemia

Developmental/learning disorders

Caffeine related side effects

Pancreatic insufficiency

Arthritis

Alcohol related side effects

Gall bladder/liver disease

Seizures

Migraine headache (some)

Anatomic defects (hiatal hernia, other GER, TEF, etc.)

Inflammatory bowel disease

 

Gustatory rhinitis

Irritable bowel syndrome

 

Psychological conditions (anorexia nervosa, bulimia, anxiety, etc.)

 

 

Auriculotemporal syndrome

 



IgE-mediated reactions are the most common FAs and the ones with which practitioners and patients are most familiar. Immediate hypersensitivity reactions result when mast cell-bound IgE is cross-linked by antigen. Cross-linking rapidly activates the IgE receptor with the release of pre-formed mediators including histamine and tryptase. Onset of IgE-mediated food reactions is almost always within 1-2 hours and usually much faster, even within 20-30 minutes, although reactions might not peak that rapidly.

Most mast cells live at surfaces interfacing the outside world (skin, eyes, respiratory tract, GI tract, and to a lesser extent bladder and uterus). The signs and symptoms of IgE-mediated food allergy reflect mast cell activation at those sites (Table 3). About 90-95% of FA reactions include but are not limited to cutaneous or gastrointestinal signs and symptoms.

Anaphylaxis is the involvement of two or more body systems or hypotension after ingestion of a known food allergen. Systemic absorption of mediators released locally, cross-linking of IgE bound to circulating basophils, and activation of the kinin system might all contribute to cardiovascular signs including tachycardia, hypotension, and shock.

Table 3: Signs and symptoms of mast cell activation.

Body system

Signs and symptoms

Cutaneous

Flushing, urticaria, pruritus, angioedema

Respiratory:

     Nose

Congestion, discharge, sneezing, pruritus

     Laryngeal*

Dysphonia, stridor, dyspnea, asphyxiation

     Pulmonary*

Dyspnea, wheeze, cough, congestion, tightness, asphyxiation

Gastrointestinal

Nausea, vomiting, bloating, cramping, diarrhea

Cardiovascular*

Tachycardia, hypotension, shock, bradycardia, cardiovascular collapse

Other

Urinary urgency, uterine cramping

* Can be potentially life threatening



MIXED IgE/NON-IgE-MEDIATED FOOD ALLERGIES

In some conditions, FA is IgE-mediated and/or non-IgE-mediated. The identification of the IgE mediated component (if present) is as described above. However, identification of foods causing presumably T cell mediated reactions can be difficult and often depends on the history, diary keeping, diagnostic suspicion, and a knowledge of the most common (but not only) foods that cause the condition. Recognizing that the best test for ANY adverse reaction to a food is what happens with ingestion, we are often left to make recommendations without any objective measures when we don’t know the mechanism.

A complete review of these disorders is beyond the scope of this article, but how FA contributes to them warrants discussion.

Not a day goes by in a busy pediatric office when no food allergic children or parents concerned about food allergy are seen. Although 10-25% of people believe they or their children have food allergy, only 5-8% of children and 1-3% of the general population are allergic. The prevalence is highest in infants and toddlers with moderate to severe atopic dermatitis, patients with certain pollen allergies, and some patients allergic to latex.

The aim of this paper is differentiate what is and is not food allergy by defining the term and distinguishing it from non-allergic reactions by means of identifying common food allergens, classifying mechanisms of food allergy, their presentations, and by discussing the utility and interpretation of testing.


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