(Along with their “Sidekicks:” garlic, scallions, shallots, leeks, chives)
A source of:
- Fructans (including inulin)
- Vitamin E
- Vitamin C
- Diallyl sulfide
It’s hard to imagine a culinary life without onions. A staple of so many cuisines, onions lend a unique savory and pungent flavor to an endless variety of dishes. Eaten cooked and raw, available all year round, onions are hard to avoid, and once you know about their considerable health benefits, it’s difficult to imagine why anyone would want to.
While onions’ health-promoting abilities have long been recognized, it’s only recently that their considerable curative abilities have been conclusively demonstrated and thus their elevation to SuperFoods status.
Onions are a major source of two phytonutrients that play a significant role in health promotion: flavonoids and the mixture of more than fifty sulfur-containing compounds. The two flavonoid subgroups found in onions are the anthocyanins that impart a red-purple color to some varieties, and the flavonoids, such as quercetin and its derivatives, that are responsible for the yellow flesh and brown skins of many other varieties. In general, the phytonutrients in onions, and in other fruits and vegetables, are concentrated in the skin and outermost portions of the flesh.
We know that the health-promoting compounds in onions, like those in garlic, are separated by cell walls. Slicing an onion ruptures these walls and releases the compounds, which then combine to form a powerful new compound: thiopropanal sulfoxide. In addition, this substance also gives cut onions their pungent aroma and their ability to make us cry.
To get the most health benefits from onions, let them sit for 5 to 10 minutes after cutting and before cooking. Heat will deactivate the thiopropanol sulfoxide and you want to give it time to develop fully and to become concentrated before eating.
Onions are high in flavonoid antioxidants, particularly quercetin (which was discussed under broccoli). Most of the onion’s quercetin is in the outermost layer, just beneath the papery skin, so peel just enough but not too much to get the most out of your onion. Also, when cooking onions to make soup, the quercetin is not lost; it is just transferred to the liquid. Drink up!
Onions and Your Heart
As with garlic, onion consumption has been shown to lower high cholesterol levels and high blood pressure. Onions, along with tea, apples, and broccoli—the richest dietary sources if flavonoids—have been shown to reduce the risk of heart disease by 20 percent in one recent meta-analysis that reviewed the dietary patterns and health of more than 100,000 individuals.
Onions and Cancer
Regular consumption of onions has also been associated with a reduced risk of colon cancer. It is believed that quercetin in onions is the protective factor, since it’s been shown to stop the growth of tumors in animals and to protect colon cells from the negative effects of some cancer-promoting substances. There’s also evidence that onions may lower the risk of cancers of the brain, esophagus, lung, and stomach.
Onions as Anti-Inflammatories
Onions contain several anti-inflammatory compounds that contribute to reducing the symptoms associated with a host of inflammatory conditions like osteoarthritis and rheumatoid arthritis, the allergic inflammatory response of asthma, and the respiratory congestion that is a symptom of the common cold. Onions and garlic both contain compounds that inhibit the enzymes that generate inflammatory prostaglandins and thromboxanes. Both vitamin C and quercetin contribute to this beneficial effect. They work synergistically to spell relief from inflammation, making both onions and garlic good choices as ingredients in many dishes during the cold and flu season. Onions also exhibit antimicrobial activity against a range of bacteria and fungi.
*This brief summary contains copyrighted material from SuperFoods HealthStyle by Steven G. Pratt, M.D. and Kathy Matthews. Copyright © 2006 by Steven G. Pratt, M.D. and Kathy Matthews Inc., published by HarperCollins; and from SuperFoods Rx For Pregnancy by Steven Pratt, M.D. Copyright © 2013 by SuperFoods Partners, LLC, published by Wiley. All rights reserved.