A set of conditions where a particular food or food component cannot be digested properly, often causing malabsorption syndromes. They include lactose intolerance, caused by shortage of a brush-border enzyme in the gut wall, and histamine intolerance from impaired breakdown of dietary histamine. Exclusion of the offending food from the diet can eliminate symptoms. Lactose intolerance reflects declining lactase after weaning in most of the world’s population, managed with lactose-free dairy or lactase supplements rather than dairy avoidance. Coeliac disease is strictly an autoimmune disorder — not an intolerance — requiring lifelong gluten exclusion; non-coeliac gluten sensitivity remains diagnostically contested, and FODMAP intolerances explain many irritable-bowel symptoms.