Food intolerances—a diagnostic challenge

Background: Food-associated complaints in the gastrointestinal tract can be signs of an intolerance of different etiology, which is reported by almost a quarter of the population. Due to the unspecific symptoms, a whole range of different triggers and immune reactions can be considered for the differential diagnosis, which cannot always be determined unambiguously and quickly. Differentiation and diagnosis of disease entity: The time course in connection with the clinical picture already allows a rough estimation of the underlying pathomechanism and points the diagnostic way. Thus, immune-mediated clinical pictures such as allergy must be distinguished from nonimmune-mediated intolerances. An allergic reaction can be IgE-mediated or cellularly induced. Secondary food allergies are triggered by other allergens than primary allergies, differ in their sensitization routes and course of disease. Non-immunological intolerance reactions also play a not insignificant role, including carbohydrate utilization disorders and histamine intolerance in addition to toxic reactions. Often difficult to identify are also those food components which trigger a nonspecific mast cell activation. Due to their particular clinical relevance, wheat intolerances of different pathogenesis are also discussed. As a consequence of their complexity with regards to disease-causing proteins, target organ manifestations, pathomechanisms and diagnostic clarification, these require a particularly differentiated approach. Purpose: This review article presents the current recommendations regarding the diagnosis of food intolerance and food allergy, with a separate focus on the specifics in the interpretation of different tests including IgE diagnostics.