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Onions

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:

Maui Onions - April through June

Vidalia Onions - May and June

Walla Walla - July and August

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.

 


Health Benefits

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 consuming refined sugars, white flour products, and lack of exercise. One cup of raw onion contains almost 20% of the Daily Value for this important trace mineral.

Cardiovascular Benefits

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 recent 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. (October 24, 2003)

Colon Cancer Prevention

The regular use 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 in certain ways.

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.

Description

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 that 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 Walla Walla, Vidalia and Maui Sweet onion. 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.

History

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 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, and from there, their cultivation spread 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. (December 17, 2004)

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 perforated 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:

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 phytochemical 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 enxyme 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 phytochemicals 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.

Safety

Onions are not a commonly allergenic food, are not included in the list of 20 foods that most frequently contain pesticide residues, and are also not known to contain goitrogens, oxalates, or purines.

Nutritional Profile

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 amount represents; the nutrient density rating; and, the food's World's Healthiest Foods Rating. Not all of our Daily Value standards are obtained from the FDA. In most instances, we used FDA Daily Values when available because they are widely recognized and apply to both men and women. However, when unavailable, we've used other science-based research to establish nutritional standards. Underneath the chart is a table that summarizes how the ratings were devised. Read more about our Food and Recipe Rating System.

 

Onions, Raw
1.00 cup
60.80 calories
Nutrient Amount DV
(%)
Nutrient
Density
World's Healthiest
Foods Rating
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
World's Healthiest
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%

In Depth Nutritional Profile for Onions

References

  • Ali M, Thomson M, Afzal M. Garlic and onions: their effect on eicosanoid metabolism and its clinical relevance. Prostaglandins Leukot Essent Fatty Acids. 2000 Feb;62(2):55-73. Review.
  • Augusti KT. Therapeutic values of onion (Allium cepa L.) and garlic (Allium sativum L.). Indian J Exp Biol. 1996 Jul;34(7):634-40. Review.
  • Challier B, Perarnau JM, Viel JF. Garlic, onion and cereal fibre as protective factors for breast cancer: a French case-control study. Eur J Epidemiol 1998 Dec;14(8):737-47.
  • Dorant E, van den Brandt PA, Goldbohm RA. A prospective cohort study on the relationship between onion and leek consumption, garlic supplement use and the risk of colorectal carcinoma in The Netherlands. Carcinogenesis 1996 Mar;17(3):477-84.
  • Dorsch W, Ettl M, Hein G, et al. Antiasthmatic effects of onions. Inhibition of platelet-activating factor-induced bronchial obstruction by onion oils. Int Arch Allergy Appl Immunol. 1987;82(3-4):535-6.
  • Ensminger AH, Ensminger, ME, Kondale JE, Robson JRK. Foods & Nutriton Encyclopedia. Pegus Press, Clovis, California.
  • Ensminger AH, Esminger M. K. J. e. al. Food for Health: A Nutrition Encyclopedia. Clovis, California: Pegus Press; 1986.
  • Fortin, Francois, Editorial Director. The Visual Foods Encyclopedia. Macmillan, New York.
  • Fukushima S, Takada N, Hori T, Wanibuchi H. Cancer prevention by organosulfur compounds from garlic and onion. J Cell Biochem Suppl 1997;27:100-5.
  • Gee JM, Hara HT. Suppression of Intestinal Crypt Cell Proliferation and Aberrant Crypt Foci by Dietary Quercetin in Rats. Nutr Cancer 2002;43(2):121-126.
  • Grieve M. A Modern Herbal. Dover Publications, New York.
  • Huxley RR, Neil HAW. The relation between dietary flavonol intake and coronary heart disease mortality: a meta-analysis of prospective cohort studies,. European Journal of Clinical Nutrition (2003) 57, 904-908.
  • Moon JH, Nakata R, Oshima S, et al. Accumulation of quercetin conjugates in blood plasma after the short-term ingestion of onion by women. Am J Physiol Regul Integr Comp Physiol. 2000 Aug;279(2):R461-7.
  • Riley DM, Bianchini F, Vainio H. Allium vegetables and organosulfur compounds: do they help prevent cancer. Environ Health Perspect 2001 Sep;109(9):893-902.
  • Sheela CG, Kumud K, Augusti KT. Anti-diabetic effects of onion and garlic sulfoxide amino acids in rats. Planta Med. 1995 Aug;61(4):356-7.
  • Vanderhoek J, Makheja A, Bailey J. Inhibition of fatty acid lipoxygenases by onion and garlic oils: Evidence for the mechanism by which these oils inhibit platelet aggregation. Bioch Pharmacol 29 (1980):3169-73.
  • Wagner H, Dorsch W, Bayer T, et al. Antiasthmatic effects of onions: inhibition of 5-lipoxygenase and cyclooxygenase in vitro by thiosulfinates and "Cepaenes". Prostaglandins Leukot Essent Fatty Acids. 1990 Jan;39(1):59-62.
  • Wood, Rebecca. The Whole Foods Encyclopedia. New York, NY: Prentice-Hall Press; 1988.
  • Yang J, Meyers KJ, van der Heide J, Liu RH. Varietal Differences in Phenolic Content and Antioxidant and Antiproliferative Activities of Onions. J Agric Food Chem. 2004 Nov 3;52(22):6787-6793.

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