Gastrointestinal symptoms
Allergy to foods continues to be a topic of debate among clinicians as to its existence, diagnosis and treatment. Every conceivable gastrointestinal symptom, including diarrhoea, vomiting, colic, constipation, bloody stools, flatus (excess gas), abdominal pain, and regurgitation may be attributed to food allergy.
Gastrointestinal allergy is more common than other disorders, especially in early childhood. The symptoms are closely associated with food intake and there is evidence of specific IgE formation to offending foods.
The most common cause of gastrointestinal allergy in infancy is cow’s milk protein, since this is the first protein to which babies may be exposed. However, other proteins such as egg white, soy protein, fish and peanut also have the potential for causing gastrointestinal 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.
Various gastrointestinal disorders of childhood may be confused with allergy:
- Lactose intolerance: This disorder is caused by a deficiency of the enzyme lactase in the small bowel mucosa. The patients suffer from diarrhoea, abdominal distension and cramps after the ingestion of milk. Lactase deficiency is screened for by using the lactose tolerance test.
- Cystic fibrosis: In early life, the diarrhoea 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.
- Coeliac disease: May be classified as a non-IgE mediated allergy or autoimmune disease. The disease is diagnosed by demonstration of IgA and IgG antibodies to gliadin, small bowel biopsy revealing a flat lesion in the small intestine (villous atrophy), and improvement of symptoms as a response to a gluten-free diet.
Adverse reactions to food
The concept "adverse reactions to food" is not easily defined, since it refers to any abnormal response to food. Adverse reactions to food are prevalent in all age groups, although the symptoms and triggering factors vary.
For the sake of clarity, adverse reactions to food are classified by the European Academy of Allergy and Clinical Immunology (EAACI) and defined as follows (1):
Toxic food reactions are not dependent on individual susceptibility, but result from general human toxicity to substances naturally present in or contaminating foods. Non toxic food reactions depend on an individual's susceptibility to certain foods and are caused by both immune-mediated (food allergy) or non immune-mediated (food intolerance) reactions. Food allergy includes IgE-mediated reactions as well as non IgE-mediated reactions. Celiac disease is defined as a non IgE immune- mediated reaction, although the immunopathogenesis of this disease is still unclear. Non immune-mediated food adverse reactions, when proven by provocation tests and a clear history, lack evidence of an immunological mechanism. The cause could be enzymatic defects, pharmacologically active substances present in the food, or remain undefined.
Food aversion refers to psychological (psychosomatic) factors that can lead a patient to a false conviction that symptoms are the results of food allergy. Food aversion is often associated with an unpleasant physical reaction caused by emotions associated with a food, rather than by the food itself. Such reactions do not occur when the food is given in an unrecognizable form.
Besides IgE-mediated reactions, it is crucial for an allergist to be aware also of non IgE-mediated and non immune-mediated adverse reactions, as the symptoms are often the same in individuals and could be misleading. Confirmation of food allergy by in vitro tests and food challenge tests gives objective measurements helpful in differential diagnosis.
An accurate diagnosis is necessary in order to be able to eliminate the right food from the diet. This is especially important when there is a risk of undernourishment or anaphylaxis.
It has been suggested that the IgE-mediated reaction to food is the most common cause of anaphylaxis, and that more people die from food-induced anaphylaxis than from insect stings.