written by Dr. Mercola
[source: Mercola.com]
Eighty-seven percent of U.S. adults say they like onions, which is great news since they're one of the healthiest foods you can eat. Rich in vitamin C, sulphuric compounds, flavonoids, and other phytochemicals, an onion a day may help keep the doctor away.
Onions are surprisingly high in beneficial polyphenols, which play an important role in preventing and reducing the progression of diabetes, cancer, and neurodegenerative and cardiovascular diseases.
Polyphenols also play an important role as a prebiotic, increasing the ratio of beneficial bacteria in your gut, which is important for health, weight management, and disease prevention.
Onions contain more polyphenols than even garlic or leeks, and are one of the best sources of a type of polyphenol called flavonoids, especially the flavonoid quercetin.
Onions Provide Disease-Fighting Quercetin
Quercetin is a powerful antioxidant with anti-inflammatory properties that may help fight chronic diseases like heart disease and cancer. In lab studies, quercetin was shown to prevent histamine release (histamines are the chemicals that cause allergic reactions.
This makes quercetin-rich foods like onions "natural antihistamines." In addition, quercetin may:
While apples and tea also contain quercetin, onions appear to be a particularly good source. Research from Wageningen Agricultural University in the Netherlands showed quercetin absorption from onions is double that from tea and three times that from apples.
Research from the University also showed consuming onions leads to increased quercetin concentrations in the blood. As reported by The World's Healthiest Foods:
"… [O]n an ounce-for-ounce basis, onions rank in the top 10 of commonly eaten vegetables in their quercetin content. The flavonoid content of onions can vary widely, depending on the exact variety and growing conditions.Although the average onion is likely to contain less than 100 milligrams of quercetin per 3-1/2 ounces, some onions do provide this amount.And while 100 milligrams may not sound like a lot, in the United States, moderate vegetable eaters average only twice this amount for all flavonoids (not just quercetin) from all vegetables per day."
Quercetin is available in supplement form, but there are a couple of reasons why getting this flavonoid from onions makes more sense:
One animal study found that animals received greater protection against oxidative stress when they consumed yellow onion in their diet as opposed to consuming quercetin extracts.Quercetin is not degraded by low-heat cooking, such as simmering. When preparing a soup with onions, the quercetin will be transferred into the broth of the soup, making onion soup an easy-to-make superfood.
Onions Provide the Valuable Prebiotic Inulin and May Help Prevent Ulcers
Prebiotics are indigestible to you, but they help nourish beneficial bacteria in your body. These beneficial bacteria in turn assist with digestion and absorption of your food, and play a significant role in your immune function. One such prebiotic is inulin, a water-soluble form of dietary fiber that's found in onions.
Inulin has multiple benefits to your health. Among obese women, consuming inulin beneficially changed the gut microbiota composition in a way that might help promote weight loss or lower the risk of diabetes.
Further, among women with type 2 diabetes, those who took inulin had improved glycemic control and increased antioxidant activity. Inulin may even help relieve constipation. Flavonoid-rich foods like onions may also inhibit the growth of H. pylori, a type of bacteria responsible for most ulcers.
Up to 20 percent of Americans over the age of 40 have H. pylori living in their digestive tract, although most will not develop ulcers. Eating onions and other flavonoid-rich foods may lower your risk further.
What Else Are Onions Good For?
Onions, which are very popular in French cuisine, are thought to play a role in the so-called "French Paradox" — the low incidence of heart disease among the French, despite their relatively high-calorie diet.
The sulfur compounds in onions, for instance, are thought to have anti-clotting properties as well as help to lower cholesterol and triglycerides. The allium and allyl disulphide in onions have also been found to decrease blood vessel stiffness by releasing nitric oxide.
This may reduce blood pressure, inhibit platelet clot formation and help decrease the risk of coronary artery disease, peripheral vascular diseases and stroke. The quercetin in onions is also beneficial, offering both antioxidant and anti-inflammatory properties that may boost heart health.
Further, as reported by the National Onion Association, onions are considered a dietary anti-carcinogen:
"The inhibitory effects of onion consumption on human carcinoma have been widely researched …In a review on the effects of quercetin … persons in the highest consumption category versus the lowest had a 50 percent reduced risk of cancers of the stomach and alimentary and respiratory tracts.Organosulfur compounds [in onions] such as diallyl disulfide (DDS), S-allylcysteine (SAC), and S-methylcysteine (SMC) have been shown to inhibit colon and renal carcinogenesis.… Mechanisms of protection ranged from induced cancer cell apoptosis and gene transcription inhibition to protection against UV-induced immunosuppression."
The many phytochemicals and other nutrients in onions work together to provide synergistic health benefits that reach body-wide. For instance, research has show including onions in your diet may offer the following benefits:
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