Producing a biological effect in living tissue or organisms, the defining property of the food components that do more than supply calories. Bioactive compounds include polyphenols, carotenoids, glucosinolates, peptides, and plant sterols, each interacting with human physiology in specific ways: modulating inflammation, influencing cholesterol, or affecting cell signaling. The term distinguishes these functional components from basic nutrients, though the boundary blurs, since vitamins are bioactive by definition. Food companies prize bioactives as the basis for functional food claims, while researchers work to establish which effects are real, at what doses, and in whom. The concept has shifted nutrition from preventing deficiency toward optimizing health through the thousands of bioactive compounds in ordinary foods.