Onions not only provide flavor, they also provide important nutrients and health-promoting phytochemicals. Plenty of onion health research provides strong evidence of its nutritional value.Antioxidants are compounds that help delay or slow the oxidative damage to cells and tissue of the body. Studies have indicated that quercetin helps to eliminate free radicals in the body, to inhibit low-density lipoprotein oxidation (an important reaction in the atherosclerosis and coronary heart disease), to protect and regenerate vitamin E (a powerful antioxidant), and to inactivate the harmful effects of chelate metal ions.