World's Healthiest Foods
The World's Healthiest Foods
George Matelijan Foundation
What would a kitchen be without the distinctively pungent smell and taste of onions filling out the flavors of almost every type of cuisine imaginable? Fortunately, yellow storage onions are available throughout the year but sweet varieties have a much more limited growing season and are available only a few months out of the year.
The word onion comes from the Latin word unio for "single," or "one," because the onion plant produces a single bulb, unlike its cousin, the garlic, that produces many small bulbs. The name also describes the union (also from unio) of the many separate, concentrically arranged layers of the onion.
Onions, like garlic, are members of the Allium family, and both are rich in powerful sulfur-containing compounds that are responsible for their pungent odors and for many of their health-promoting effects. Onions contain allyl propyl disulphide, while garlic is rich in allicin, diallyl disulphide, diallyl trisulfide and others. In addition, onions are very rich in chromium, a trace mineral that helps cells respond to insulin, plus vitamin C, and numerous flavonoids, most notably, quercitin.
Blood Sugar-Lowering Effects
The higher the intake of onion, the lower the level of glucose found during oral or intravenous glucose tolerance tests. Experimental and clinical evidence suggests that allyl propyl disulfide is responsible for this effect and lowers blood sugar levels by increasing the amount of free insulin available. Allyl propyl disulfide does this by competing with insulin, which is also a disulphide, to occupy the sites in the liver where insulin is inactivated. This results is an increase in the amount of insulin available to usher glucose into cells causing a lowering of blood sugar.
In addition, onions are a very good source of chromium, the mineral component in glucose tolerance factor, a molecule that helps cells respond appropriately to insulin. Clinical studies of diabetics have shown that chromium can decrease fasting blood glucose levels, improve glucose tolerance, lower insulin levels, and decrease total cholesterol and triglyceride levels, while increasing good HDL-cholesterol levels. Marginal chromium deficiency is common in the United States, not surprising since chromium levels are depleted by the consumption refined sugars and white flour products as well as the lack of exercise. One cup of raw onion contains over 20% of the Daily Value for this important trace mineral.
The regular consumption of onions has, like garlic, been shown to lower high cholesterol levels and high blood pressure, both of which help prevent atherosclerosis and diabetic heart disease, and reduce the risk of heart attack or stroke. These beneficial effects are likely due to onions' sulfur compounds, its chromium and its vitamin B6, which helps prevent heart disease by lowering high homocysteine levels, another significant risk factor for heart attack and stroke.
Onions have been singled out as one of the small number of vegetables and fruits that contributed to the significant reduction in heart disease risk seen in a meta-analysis of seven prospective studies. Of the more than 100,000 individuals who participated in these studies, those who diets most frequently included onions, tea, apples and broccoli-the richest sources of flavonoids-gained a 20% reduction in their risk of heart disease.
Support Gastrointestinal Health
The regular consumption of onions, as little as two or more times per week, is associated with a significantly reduced risk of developing colon cancer. Onions contain a number of flavonoids, the most studied of which, quercitin, has been shown to halt the growth of tumors in animals and to protect colon cells from the damaging effects of certain cancer-causing substances. Cooking meats with onions may help reduce the amount of carcinogens produced when meat is cooked using high heat methods.
Quercitin, an antioxidant in onions, and curcumin, a phytonutrient found in the curry spice turmeric, reduce both the size and number of precancerous lesions in the human intestinal tract, suggests research published in Clinical Gasteroenterology and Hepatology.
Five patients with an inherited form of precancerous polyps in the lower bowel known as familial adenomatous polyposis (FAP) were treated with regular doses of curcumin and quercetin over an average of six months. The average number of polyps dropped 60.4%, and the average size of the polyps that did develop dropped by 50.9%.
FAP runs in families and is characterized by the development of hundreds of polyps (colorectal adenomas) and, eventually, colon cancer. Recently, nonsteroidal anti-inflammatory drugs (NSAIDs such as aspirin, ibuprofen) have been used to treat some patients with this condition, but these drugs often produce significant side effects, including gastrointestinal ulcerations and bleeding, according to lead researcher Francis M. Giardiello, M.D., at the Division of Gastroenterology, Johns Hopkins University.
Previous observational studies in populations that consume large amounts of curry, as well as animal research, have strongly suggested that curcumin, one of the main ingredients in Asian curries, might be effective in preventing and/or treating cancer in the lower intestine. Similarly, quercetin, an anti-oxidant flavonoid found in a variety of foods including onions, green tea and red wine, has been shown to inhibit growth of colon cancer cell lines in humans and abnormal colorectal cells in animals.
In this study, a decrease in polyp number was observed in four of five patients at three months and four of four patients at six months.
Each patient received curcumin (480 mg) and quercetin (20 mg) orally 3 times a day for 6 months. Although the amount of quercetin was similar to what many people consume daily, the curcumin consumed was more than would be provided in a typical diet because turmeric only contains on average 3-5 % curcumin by weight. While simply consuming curry and onions may not have as dramatic an effect as was produced in this study, this research clearly demonstrates that liberal use of onions and turmeric and onions can play a protective role against the development of colorectal cancer.
Onion and Garlic Protective against Many Cancers
Making onion and garlic a staple in your healthy way of eating may greatly lower your risk of several common cancers, suggests a large data set of case-control studies from Southern European populations (Galeone C, Pelucchi C et al, American Journal of Clinical Nutrition).
Study participants consuming the most onions showed an 84% reduced risk for cancer of the oral cavity and pharynx, 88% reduced risk for esophageal cancer, 56% reduced risk for colorectal cancer, 83% reduced risk for laryngeal cancer, 25% reduced risk for breast cancer, 73% reduced risk for ovarian cancer, 71% reduced risk for prostate cancer, and 38% reduced risk for renal cell cancer, compared to those eating the least onions. Similarly, those eating the most garlic had a 39% reduced risk for cancer of the oral cavity and pharynx, 57% reduced risk for esophageal cancer, 26% reduced risk for colorectal cancer, 44% reduced risk for laryngeal cancer, 10% reduced risk for breast cancer, 22% reduced risk for ovarian cancer, 19% reduced risk for prostate cancer, and 31% reduced risk for renal cell cancer, compared to those eating the least garlic.
Onions Protective against Ovarian Cancer
Research calculating flavonoid intake in 66,940 women enrolled in the Nurses Health Study between 1984 and 2002 revealed that women whose diets provided the most kaempferol had a 40% reduction in risk of ovarian cancer, compared to women eating the least kaempferol-rich foods. In addition to onions, foods richest in kaempferol include tea (nonherbal), broccoli, curly kale, leeks, spinach, and blueberries.
A significant 34% reduction in ovarian cancer risk was also seen in women with the highest intake of the flavone luteolin (found in citrus). Int J Cancer. 2007 Apr 30; Am J Clin Nutr. 2004 May;79(5):727-47.
Boost Bone Health
Milk isn't the only food that boosts bone health. Onions also help maintain healthy bones, suggests a study published in the Journal of Agricultural and Food Chemistry.
A compound newly identified in onions with the long complex name of gamma-L-glutamyl-trans-S-1-propenyl-L-cysteine sulfoxide, GPCS, for short, inhibits the activity of osteoclasts (the cells that break down bone). The more GPCS given in this animal study, the more the bone resorptive (breakdown) action of osteoclasts was inhibited.
Onions may be especially beneficial for women, who are at increased risk for osteoporosis as they go through menopause. Fosamax (Alendronate), the drug typically prescribed to prevent excessive bone loss, works in a similar manner, by destroying osteoclasts, so they do not break down bone. Potential negative side effects of Fosamax include irritation of the upper gastrointestinal mucosa, acid regurgitation, esophageal ulcers and erosions. Potential negative side effects of eating onions: onion breath.
Anti-Inflammatory and Anti-Bacterial Activity
Several anti-inflammatory agents in onions render them helpful in reducing the severity of symptoms associated with inflammatory conditions such as the pain and swelling of osteo- and rheumatoid arthritis, the allergic inflammatory response of asthma, and the respiratory congestion associated with the common cold. Both onions and garlic contain compounds that inhibit lipoxygenase and cyclooxygenase (the enzymes that generate inflammatory prostaglandins and thromboxanes), thus markedly reducing inflammation. Onions' anti-inflammatory effects are due not only to their vitamin C and quercitin, but to other active components called isothiocyanates. These compounds work synergistically to spell relief from inflammation. In addition, quercitin and other flavonoids found in onions work with vitamin C to help kill harmful bacteria, making onions an especially good addition to soups and stews during cold and flu season.
Onions may bring a tear to your eye, and a pungency to your breath, but they will most certainly bring delight to your tastebuds. The onion, known scientifically as Allium cepa, is, on the surface, a humble brown, white or red, paper-thin skinned bulb; yet, despite its plain looks, has an intense flavor and is a beloved part of the cuisine of almost every region of the world. The word onion comes from the Latin word unio for "single," or "one," because the onion plant produces a single bulb, unlike its cousin, the garlic, that produces many small bulbs. The name also describes the onion bulb when cut down the middle; it is a union (also from unio) of many separate, concentrically arranged layers.
Onions range in size, color and taste depending upon their variety. There are generally two types of large, globe-shaped onions, classified as spring/summer or storage onions. The former class includes those that are grown in warm weather climates and have characteristic mild or sweet tastes. Included in this group are the Maui Sweet Onion (in season April through June), Vidalia (in season May through June) and Walla Walla (in season July and August). Storage onions are grown in colder weather climates and, after harvesting, are dried out for a period of several months, attaining dry, crisp skins. They generally have a more pungent flavor and are usually named by their color: white, yellow or red. Spanish onions fall into this classification. In addition to these large onions, there are also smaller varieties such as the green onion, or scallion, and the pearl onion.
Onions are native to Asia and the Middle East and have been cultivated for over five thousand years. Onions were highly regarded by the Egyptians. Not only did they use them as currency to pay the workers who built the pyramids, but they also placed them in the tombs of kings, such as Tutankhamen, so that they could carry these gifts bestowed with spiritual significance with them to the afterlife.
Onions have been revered throughout time not only for their culinary use, but also for their therapeutic properties. As early as the 6th century, onions were used as a medicine in India. While they were popular with the ancient Greeks and Romans, they were oftentimes dressed with extra seasonings since many people did not find them spicy enough. Yet, it was their pungency that made onions popular among poor people throughout the world who could freely use this inexpensive vegetable to spark up their meals. Onions were an indispensable vegetable in the cuisines of many European countries during the Middle Ages and later even served as a classic healthy breakfast food. Christopher Columbus brought onions to the West Indies; their cultivation spread from there throughout the Western Hemisphere. Today China, India, the United States, Russian, and Spain are among the leading producers of onions.
How to Select and Store
Onions are a major source of both phenols and flavonoids, phytonutrients that numerous population studies have shown are protective against both cardiovascular disease and cancer. Research published in the November 2004 issue of the Journal of Agricultural and Food Chemistry shows that the variety of onions you choose and the way you prepare them can make a huge difference in the amount of beneficial compounds, and the antioxidant and anti-cancer effects, they deliver.
Shallots and 10 other onion (Allium cepa L.) varieties commonly available in the United States were evaluated: Western Yellow, Northern Red, New York Bold, Western White, Peruvian Sweet, Empire Sweet, Mexico, Texas 1015, Imperial Valley Sweet, and Vidalia.
In general, the most pungent onions delivered many times the benefits of their milder cousins.
Shallots had the most phenols, 6 times the amount found in Vidalia onion, the variety with the lowest phenolic content. Shallots also had the most antioxidant activity, followed by Western Yellow, New York Bold, Northern Red, Mexico, Empire Sweet, Western White, Peruvian Sweet, Texas 1015, Imperial Valley Sweet, and Vidalia.
Western Yellow onions had the most flavonoids, 11 times the amount found in Western White, the variety with the lowest flavonoid content.
For all varieties of onions, the more phenols and flavonoids they contained, the more antioxidant and anti-cancer activity they provided.
When tested against liver and colon cancer cells, Western Yellow, New York Bold and shallots were most effective in inhibiting their growth. The milder-tasting varieties, Western White, Peruvian Sweet, Empire Sweet, Mexico, Texas 1015, Imperial Valley Sweet, and Vidalia, showed little cancer-fighting ability. So, next time your eyes water when you're slicing onions, be glad. The onion you're cutting is likely to be loaded with beneficial phytonutrients.
Choose onions that are clean, well shaped, have no opening at the neck and feature crisp, dry outer skins. Avoid those that are sprouting or have signs of mold. In addition, onions of inferior quality often have soft spots, moisture at their neck, and dark patches, which may all be indications of decay. As conventionally grown onions are often irradiated to prevent them from sprouting, purchase organically grown varieties since these are not treated with this process.
When purchasing scallions, look for those that have green, fresh-looking tops that appear crisp, yet tender. The base should be whitish in color for two or three inches. Avoid those that have wilted or yellowed tops.
Onions should be stored at room temperature, away from bright light, and in a manner where they are well ventilated. To do this, either place them in a wire hanging basket or a perforated bowl with a raised base so that air can circulate underneath. The length of storage varies with the type of onion. Those that are more pungent in flavor, such as yellow onions, can stay longer than those with a sweeter taste, such as white onions, since the compounds that confer their sharp taste help to preserve them. Scallions should be stored in a plastic bag in the refrigerator where they will keep for about one week. All onions should be stored away from potatoes, as they will absorb their moisture and ethylene gas, causing them to spoil more readily.
The remainder of cut onions should be wrapped tightly in plastic or in a sealed container and should be used within a day or two since they tend to oxidize and lose their nutrient content rather quickly. Cooked onions will best maintain their taste in an airtight container where they can be kept for a few days; they should never be placed in a metal storage container as this may cause them to discolor. Although peeled and chopped onions can be frozen (without first being blanched), this process will cause them to lose some of their flavor.
How to Enjoy
For some of our favorite recipes, click Recipes.
Tips for Preparing Onions:
While many people love to eat onions, most dread cutting them since this process usually brings a tear or two to the eyes. The compound that causes the eyes to burn is a phytonutrient known as allyl sulfate that is produced when sulfur-compounds released by the onion's ruptured cells are exposed to air.
If cutting onions irritates your eyes, there are a few tricks that you can employ. Chill the onions for an hour or so before cutting. This will slow the activity of the enzyme that produces the allyl sulfate and is a better choice than the traditional method of cutting onion under running water. This latter process may dilute the amount of allyl sulfate, which, while it may be irritating to the eyes, is actually one of the phytonutrients most responsible for onions significant health benefits.
Use a very sharp knife and always cut the onions while standing; that way your eyes will be as far away as possible. If cutting onions really makes you cry, consider wearing glasses or goggles.
A Few Quick Serving Ideas:
Combine chopped onions, tomatoes, avocado and jalapeno for an all-in-one guacamole salsa dip.
To perk up plain rice, sprinkle some green onions, also known as scallions, and sesame seeds on top.
Sautéed chopped onions are so versatile that they can be added to most any vegetable dish.
Enjoy a classic Italian salad-sliced onions, tomatoes and mozzarella cheese drizzled with olive oil.
Onions are not a commonly allergenic food, are not known to contain measurable amounts of oxalates or purines and are also not included in the Environmental Working Group's 2009 report "Shopper's Guide to Pesticides" as one of the 12 foods most frequently containing pesticide residues.
Introduction to Food Rating System Chart
The following chart shows the nutrients for which this food is either an excellent, very good or good source. Next to the nutrient name you will find the following information: the amount of the nutrient that is included in the noted serving of this food; the %Daily Value (DV) that that amount represents (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and, the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. Read detailed information on our Food and Recipe Rating System.
Nutrient Amount DV
Density World's Healthiest
chromium 24.80 mcg 20.7 6.1 very good
vitamin C 10.24 mg 17.1 5.1 very good
dietary fiber 2.88 g 11.5 3.4 very good
manganese 0.22 mg 11.0 3.3 good
molybdenum 8.00 mcg 10.7 3.2 good
vitamin B6 (pyridoxine) 0.19 mg 9.5 2.8 good
tryptophan 0.03 g 9.4 2.8 good
folate 30.40 mcg 7.6 2.3 good
potassium 251.20 mg 7.2 2.1 good
phosphorus 52.80 mg 5.3 1.6 good
copper 0.10 mg 5.0 1.5 good
Foods Rating Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%
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