Onion
Onion is an exceptionally strong antioxidant food. It is one of civilization’s oldest medicines. It contains several anticancer compounds. This vegetable is the richest dietary source of quercetin, a powerful antioxidant. This substance is found only in shallots, yellow and red onions and not in white. Some onions are so full of quercetin that the compound accounts for up to 10 per cent of their dry weight, according to tests by Terrance Leighton, Ph.D., professor of biochemistry and molecular biology at the University of California at Berkeley.