Food allergy and food intolerance--what is the difference?

The literature is contradictory concerning the use (and misuse) of the terms "food allergy" and "food intolerance." When using double-blind, placebo-controlled food challenge as the gold standard, the clinical picture characterizing both diseases is identical, ie, concomitant signs and symptoms from the skin, gastrointestinal-tract and respiratory system (classical allergic signs and symptoms). A distinction between food allergy and food intolerance thus depends on whether the involvement of the immune system can be verified. The basic problem with diagnostic tests such as skin prick test (SPT), measurement of specific IgE (RAST) or histamine release from basophils (HR) is that in contrast to inhalant allergens, no standardized extracts are commercially available. It is therefore often not possible to discriminate between the ability of a test per se in the diagnosis of food allergy and differences in allergen extract quality. This is probably the reason for the great variability in diagnostic sensitivity and specificity reported in the literature. Many cases of food allergy to proteins may be therefore misdiagnosed as food intolerance due to a low sensitivity of the tests (SPT, RAST, and HR) used.