Methodological issues 1021 Defining adverse food reactions

There are internationally agreed definitions for adverse food reactions, as have been discussed in Chapter 1. Unfortunately, terms such as 'food intolerance' are still used inconsistently. Thus the term 'intolerance' according to internationally agreed definitions is taken to mean physiological reactions to foods that do not have an immunological mechanism. However the term 'cows' milk protein intolerance' is often used to describe an immunological reaction to cows' milk that is non IgE-mediated (Host et al. 1997). It is not uncommon for authors to use several definitions of food allergy or food intolerance within a single publication. Any critical analysis of epidemiological studies must begin with a detailed understanding of the definitions used (for example, Table IV in Zeiger et al. 1999). This is of critical importance in comparative studies where like must be compared with like.

The international definitions of adverse food reactions exclude food aversion. Such aversions have a psychological origin and cannot be reproduced under objective conditions when the patient and observer are blinded to the identity of the food consumed. In population studies, up to a third of adults may report symptoms of adverse food reactions; however, double-blinded, placebo-controlled studies (Young et al. 1994) show that the majority of these are not reproducible. This discrepancy between real and perceived adverse food reactions is likely to be accounted for by the large number of subjects who have food aversion. The failure to differentiate between food aversion and reproducible adverse food reactions in studies relying on self-reporting (Bjornsson et al. 1996) or open challenges (Crespo et al. 1995) must be considered when prevalence data is assessed.

In this chapter we will focus on food allergies as this form of adverse food reaction is the best studied and associated with the highest morbidity. Additionally, we will describe adverse reactions to food additives. Although any food can cause allergic reactions, most reactions are caused by a limited range of foods. In infants and young children, the commonly implicated foods are cows' milk, egg, soy, wheat and peanuts. For older children, teenagers and adults, foods such as fish and shellfish are also a significant problem.

Food Allergies

Food Allergies

Peanuts can leave you breathless. Cat dander can lead to itchy eyes, a stuffy nose, coughing and sneezing. And most of us have suffered through those seasonal allergies with horrible pollen counts. Learn more...

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