Nontoxic food reactions

These reactions are either immune-mediated or non-immune-mediated. When the reaction is immune-mediated the term 'food allergy' is applied, and when non-immune-mediated the term 'food intolerance' is recommended. Both types of reactions are reproducible and depend on an individual's susceptibility.

Food allergy

Food allergy itself can be subdivided into two categories, IgE-mediated food allergy and non-IgE-mediated food allergy (Fig. 1.1). Immunoglobulin (Ig) E, or IgE, is the main antibody involved in induction of immediate allergic reactions. Most of the research evidence available on food allergy has been focused on IgE-mediated food allergy. Indeed, most common food allergies are mediated by IgE antibodies. The mechanism underlying IgE-mediated food allergy is fairly well established. Symptoms of this form of food allergy appear rapidly, are varied and range from anaphylaxis to skin reactions.2

Non-IgE-mediated food allergy is less well understood. Such allergies include reactions involving other immunoglobulin isotypes such as IgG and its subclasses, food immune complexes and cell-mediated immunity. Diagnosing this form of food allergy has been difficult and none of the above-mentioned mechanisms have been proven to be causative by double-blind, placebo-controlled food challenges (DBPCFC).

Food intolerance

Food intolerance reactions are reproducible non-immune-mediated reactions which, depending on their causality, are divided into the following types of intolerance:

• pharmacological, i.e. reactions caused by either naturally derived or added chemicals that produce a pharmacological effect in the individual

• undefined food intolerance.

Lactase deficiency (usually referred to as lactose intolerance) is a good example of the enzymatic form of food intolerance.3 It is often secondary to other conditions such as viral gastroenteritis. In very rare situations lactase deficiency can be an inborn error of metabolism.

Examples of pharmacological forms of food intolerance include reactions to vasoactive amines, such as histamine, found in many foods. The importance of these amines in provocation of symptoms is not well defined. The third category of food intolerance reactions is 'undefined'. These reactions include any reproducible adverse reaction due to an unknown mechanism. Reactions to food additives may be considered in this category.

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