Foods and beverages contain nutrients that are essential to human life, but they also contain elements that, for some individuals, may be harmful to health or even life-threatening. Foods and beverages may cause adverse reactions when ingested, but humans also can have adverse reactions to foods through inhalation (Edwards, McConnochie, and Davies 1985; Kemp, Van Asperen, and Douglas 1988), skin contact (Mathias 1983), or injection (Flu Shots and Egg Allergy 1992; Schwartz 1992).

Sensitivity to foods may be caused by immunologic abnormalities or by other mechanisms, such as host enzyme deficiency. Food sensitivities caused by immunologic abnormalities are commonly referred to as food allergies, whereas food sensitivities caused by nonimmunologic mechanisms are referred to as food intolerances (Anderson 1990; Beaudette 1991). This chapter reviews major considerations with regard to both classifications of food sensitivities. It should also be noted that a disorder called “pseudo-food allergy syndrome” exists. This syndrome is a psychological disorder in which the sufferer believes in the existence of a food allergy that cannot be confirmed by clinical testing (Pearson and Rix 1983, Pearson 1988).

Food Allergies

Allergic, or immunologically based, reactions to food most commonly involve a Type I or IgE mediated reaction (Anderson, 1990) as classified by R. R. A. Coombs and P. G. H. Gell (1975). The stages of the Type I reaction are illustrated in Table IV.E.5.1. It has been theorized that IgE mediated reactions to food may be related to a reduction in the need to produce IgE in response to intestinal parasitic infection. This theory, known as the “mast cell saturation hypothesis,” speculates that when the majority of IgE antibodies are bound to intestinal parasites, fewer antibodies are available to bind with food antigens. Production of high levels of IgE to fight parasitism would be protective, whereas production of high levels of IgE specific for food antigens is counterproductive to health (Godfrey 1975; Merrett, Merrett, and Cookson 1976; Lieberman and Barnes 1990).