Every conceivable gastrointestinal symptom including diarrhea, vomiting, colic, constipation, bloody stools, flatulance, abdominal pain, and regurgitation has been attributed to food allergy. IgE-mediated gastrointestinal food allergy is more common than the disorders described below. The symptoms are closely associated with food intake and in such cases there is evidence of allergen-specific IgE antibody formation to identified foods.

The most common cause of gastrointestinal allergy in infancy is sensitivity to cow's milk protein, since this is the first protein to which babies are exposed. However, other proteins such as soy protein, egg white, fish, peanuts and tree nuts also have the potential for causing gastro-intestinal disease. Milk allergy usually resolves itself and is rare after the age of 2-3. Allergy to other food proteins tends to persist much longer. Oral allergy syndrome (OAS) is a food-induced gastrointestinal allergy which affects the lips and the mucosa of the pharynx. Since OAS is mostly related to tree pollen allergy, due to similar epitopes in fruit and vegetables as in pollens, it is mainly seen in older children and adults.

Various gastrointestinal disorders of childhood may be confused with IgE-mediated food allergy: Non-IgE-mediated gastrointestinal food allergy such as e.g. coeliac disease: Infants with coeliac disease are retarded in growth, especially weight, for their age and have a history of chronic diarrhea, anorexia and vomiting.

The stools are large, bulky and malodorous. The disease is diagnosed by (1) demonstration of IgA/ IgG antibodies to gliadin and/or IgA antibodies to tissue transglutaminase, (2) small bowel biopsy revealing a non-specific flat lesion and (3) response to a gluten-free diet. Treatment consists of a life-long gluten-free diet.

Lactose intolerance: This disorder is caused by a deficiency of the enzyme lactase in the small bowel mucous. The patient suffers from diarrhea, abdominal distension and cramps after the ingestion of milk. Lactase deficiency is screened for using the lactose tolerance test.

Cystic fibrosis: In early life, the diarrhea of cystic fibrosis can mimic gastrointestinal allergy. The pathophysiologic and diagnostic hallmarks of cystic fibrosis are (1) pancreatic enzyme deficiency, (2) progressive chronic obstructive, infective and destructive pulmonary disease, and (3) elevated sweat sodium and chloride concentrations. The sweat test is the only diagnostic test.

Prevalence

IgE-mediated gastrointestinal food allergy is estimated to affect between 1 and 3% of infants during their first year and about 0.5% of older children. If oral allergy syndrome (OAS) is added, the prevalence is much higher in older children and adolescents, since OAS is seen in about 50% of patients with tree pollen allergy.