Onions not only provide flavor; they also provide health-promoting phytochemicals as well as nutrients.
Onions contain quercetin, a flavonoid (one category of antioxidant compounds). 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. Major dietary sources of quercetin include tea, onions and apples. Recent studies at Wageningen Agricultural University, the Netherlands, showed that the absorption of quercetin from onions is twice that from tea and more than three times that from apples. Studies are in progress to determine whether the increased quercetin accumulation from eating onions translates into significant antioxidant benefit. Other studies have shown that consumption of onions may be beneficial for reduced risk of certain diseases. Consumption of onions may prevent gastric ulcers by scavenging free radicals and by preventing growth of the ulcer-forming microorganism, Heliobacter pylori. A recent study at the University of Bern in Switzerland showed that consumption of 1 g dry onion per day for 4 weeks increased bone mineral content in rats by more than 17% and mineral density by more than 13% compared to animals fed a control diet. This data suggests onion consumption has the potential to decrease the incidences of osteoporosis. Several studies have shown quercetin to have beneficial effects against many diseases and disorders including cataracts, cardiovascular disease as well as cancer of the breast, colon, ovarian, gastric, lung and bladder. In addition to quercetin, onions contain the phytochemicals known as disulfides, trisulfides, cepaene, and vinyl dithiins. These compounds have a variety of health-functional properties, including anticancer and antimicrobial activities. Onions are also a source of vitamin C, potassium, dietary fiber and folic acid. They also contain calcium, iron and have a high protein quality (ratio of mg amino acid/gram protein). Onions are low in sodium and contain no fat.
