What is a food intolerance?
A food intolerance or hypersensitivity is defined as an immunologically or non-immunologically mediated reaction to certain substances contained in food (European Academy of Allergy and Clinical Immunology, EAACl).
Which reactions are caused?
Immunological reactions, usually referred to as food allergies, are hypersensitivities that occur in susceptible individuals, the symptoms of which occur after repeated contact with the allergen (sensitization). These also cover lgE-mediated reactions, which are considered real food allergies, and non-lgE-mediated reactions (notably, gluten intolerance [coeliac disease, sprue]) in combination with an lgA- or lgG-mediated reaction.
Among the most important non-immunological reactions are enzymatic intolerances (enzymopathy). These are characterized by certain enzyme deficiencies or enzyme defects, which make it impossible for the individual to (fully) digest certain nutritional components. Enzyme deficiencies or defects may either be congenital or acquired. The following important enzymatic intolerances are known: lactose, fructose, sucrose and histamine intolerance.
Additional non-immunological hypersensitivities to food include pseudoallergic reactions to additives, pharmacologically active constituents as well as toxic reactions (food poisoning). The clinical picture (i.e. the symptoms) of pseudoallergies is similar to that of allergies. Pseudoallergies cause an unspecific activation and degranulation of mast cells. Typical triggers include preservatives, colourants, emulsifying agents or sulphites.
Certain substances in food, such as certain biogenic amines, glutamates or caffeine, are pharmacologically active and may lead to symptoms of a food hypersensitivity (relative intolerance), if consumed in larger quantities.