Flavonoids, distinct from flavanols, containing a hydroxyl group; they include kaempferol and quercetin. Found naturally in plants, they give ivory and yellow colours to many flowers; dietary sources include fruits, vegetables, red wine and tea, and they are believed to protect against cardiovascular disease and cancer. Quercetin from onions and apples, kaempferol from kale and myricetin from berries are the main dietary flavonols, typically present as glycosides that gut enzymes hydrolyse. They are potent in vitro antioxidants and metal chelators, though whether these mechanisms explain epidemiological associations with heart health remains debated.