Sunday 13 December 2009, 23:14

Food allergy and food intolerance

The main differences between these two food-related disorders

Food allergy and food intolerance

Adverse reactions to food affect more than 20% of the population in industrialized countries. They are caused either by food allergy or by food intolerance. Although these two food-related disorders usually cause similar symptoms and signs and are often confused with each other, their incidence and pathogenesis are quite different.


Food allergy is an immunologically mediated disease, affecting 2-5% of adults and 5-10% of children. It develops as an hypersensitivity reaction to a specific food allergen (usually a protein). When a sensitive person eats the incriminated food for the first time, his immune system reacts by creating specific antibodies (immunoglobulin E or IgE antibodies) against that food protein, however without developing any observable adverse reactions. In other words, he gets sensitized to the specific food allergen.


Once sensitized, the immune system responds to subsequent intakes of the incriminated food by producing a greater amount of allergen-specific IgE antibodies: these in turn stimulate specific cells (mast cells) to secrete hystamin, which is the substance responsible for the onset of allergic symptoms.


Food intolerance is a non-immunologically mediated disease, whose incidence (around 20-25%) is much greater than that of food allergy. Food intolerance pathogenesis is complex and may vary from case to case. It may depend either on functional or on structural causes.


Food intolerance of functional origin is usually not associated with any anatomical or morphological changes in the gastrointestinal tract. It may be caused either by toxic or non-toxic mechanisms. Toxic reactions arise through the action of chemicals or toxins (of bacterial, fungal or plant origin) contaminanting foods. Non-toxic adverse reactions derive from a wide range of mechanisms: enzymatic or transport defects (such as lactase deficiency in the small intestine), abnormal effects of pharmacological substances naturally present in some foods (salycilate and hystamin intolerance), idiosyncrasy to food additives.


Food intolerance of structural origin is due to a morphologically observable alteration in the gastrointestinal tract, leading to dysfunction in the digestive process and/or to bacterial overgrowth in the small intestine. Some examples of such structural alterations include: esophageal stricture, stomach resection, chronic pancreatitis, intestinal diverticula, small intestin infection. Obviously in these cases food intolerance may be completely overcome by treating, whenever possible, the underlying structural disorder.


Differential diagnosis between food allergy and food intolerance and among the various etiologies of food intolerance is not always easy, and several tests are often required to make the final diagnosis. However, once diagnosed, both food allergy and food intolerance may be effectively treated with the simplest existing approach: avoid eating the problem foods.


By Chiara De Carli

Category: Allergy

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