Adverse reactions to food affect about one third of the population. They are based on very different mechanisms and are triggered by specific foods. They are divided into food intolerances, which manifest mainly in the gastrointestinal tract and food allergies, which can also cause extraintestinal symptoms and have an immunological genesis. In adults, food intolerances are significantly more common than food allergies with a prevalence of approximately 10-20%. The most important food intolerances are sugar intolerances, such as lactose and fructose intolerance but intolerances to wheat also play an increasing role. The diagnostics of food intolerances require extensive exclusion diagnostics, whereby in particular irritable bowel syndrome and intestinal dysbiosis must be differentiated. The therapy of food intolerance is primarily based on a targeted elimination diet. In this advanced education article the most important food intolerances are discussed.