Understanding Onions

Onions (Allium cepa), also known as bulb onions or common onions, are the most widely cultivated species of the genus Allium, which includes chivesscallionsleeks, garlic, shallots, elephant garlic, and rakkyo. All of these species, belong, in turn, to the Amaryllidaceae family, which includes many ornamentals, such as the belladonna lily, tuberose, snowdrop, snowflake, daffodil, Cape tulip, Peruvian lily, and amaryllis.

Wild onions may have grown on every continent. Humans discovered and started eating wild onions long before farming or even writing was invented. Bulb onions have not one but four possible wild plants they could have evolved from, all of which grow in central Asia.

Onions may be one of the earliest cultivated crops because they were less perishable than other foods of the time, were transportable, were easy to grow, and could be grown in a variety of soils and climates. In addition, onions prevented thirst and could be dried and preserved for later consumption when food might be scarce. Besides their importance as a food, onions were important in art, medicine, and mummification.

In Egypt, onions can be traced back to 3500 BC. Onions grew in Chinese gardens as early as 3000 BC. The Sumerians of Mesopotamia, the first to establish a written language, grew onions as early as 2400 BC. One of their cuneiform inscriptions dating back to 2400 BC read, “The oxen of the gods plowed the city governor’s onion patches. The onion and cucumber patches of the city governor were located in the gods’ best fields.” The inscription actually referred to the property of the temple as the “gods’ best fields” that were being misused as an onion patch by the city governor.

The Code of Hammurabi, known as the ancient law of Mesopotamia, and dated around 1772 BC, provides the needy a monthly ration of bread and onions, which comprised the mainstay of the peasant diet. In Egypt, peasants ate onions extensively along with bread and beer.

Onions symbolized eternal life to the Egyptians, because of their circle-within-a-circle structure. Paintings of onions appear on the inner walls of the pyramids and in the tombs of both the Old Kingdom and the New Kingdom. Onions are mentioned as funeral offerings. Large, peeled onions and slender, immature ones are depicted on the banquet tables of the great feasts and upon the altars of the gods. Frequently, Egyptian priests are pictured holding onions in their hands or covering an altar with a bundle of their leaves or roots.  A small sect of Egyptian priests, however, were forbidden to eat them.

Onions are mentioned in some of the oldest Vedic writings from India dating from 1500 BC.

The Book of Numbers (11:15) mentions that after the Israelites left Egypt (around 1446 BC), onions were one of the foods they greatly missed, along with leeksmelonsgarlic, and cucumbers.

In mummies, onions have been found in the pelvic region, in the thorax, flattened against the ears, and in front of the collapsed eyes. Flowering onions have been found on the chest, and onions have been found attached to the soles of the feet and along the legs. King Ramses IV, who died in 1160 BC, was entombed with onions in his eye sockets. Onions may have been used because it was believed that their strong scent or magical powers would prompt the dead to breathe again. Onions were also known for their strong antiseptic qualities, which could be useful in the afterlife.

In India as early as the sixth century BC, the famous medical treatise Charaka Samhita celebrates onions as diuretics, and as good for digestion, the heart, the eyes, and the joints. Brahmins and Jains, however, are forbidden to eat onions, even today.

By 500 BC, onions were a common peasant food in Greece, along with garlic, peas, cabbage, and fava beans. The Greeks used onions to fortify athletes for the Olympic Games. Before competition, athletes would consume pounds of onions, drink onion juice, and rub onions on their bodies, because it would “lighten the balance of the blood.”

Alexander the Great (20/21 July 356 – 10/11 June 323 BC) believed that if one ate strong foods, one would become strong. Alexander fed his men onions believing they would increase their strength and courage.

By the first century, onions were suspended from strings that hung from the ceiling of the Trajan market in Rome. The Romans ate onions regularly and carried them on journeys to their provinces in England and Germany. Gladiators were rubbed down with onion juice to “firm up the muscles.” Gaius Plinius Secundus (AD 23 – August 25, AD 79), better known as Pliny the Elder, was a Roman naturalist who wrote of Pompeii’s onions and cabbages. In Pompeii those “lowly vendors” who sold onions were rejected from the guild of fruit and vegetable vendors, and had to form their own guild. Archeologists discovered a basket of overcooked onions in the ruins of one of Pompeii’s favorite brothels. Before he was overcome and killed by the volcano’s heat and fumes, Pliny catalogued the Roman beliefs about the efficacy of the onion to cure vision, induce sleep, heal mouth sores, dog bites, toothaches, dysentery, and lumbago. Excavators of Pompeii would later find gardens where, just as Pliny had said, onions had grown. The bulbs had left behind cavities in the ground. Pedanius Dioscorides (circa 40—90 AD) was a Greek who served in Rome as the chief physician of Nero’s Army. Dioscorides wrote De Materia Medica, a 5-volume encyclopedia about herbal medicine and related medicinal substances (a pharmacopeia), that was widely read for more than 1,500 years. He recommended several medicinal uses of onions. The Roman cookbook Apicius, from the 4th–5th century AD, included many references to onions, although they were never featured in dishes for the wealthy but only as flavorings in sauces or to enhance a mixed dish or a dressing.

During the Middle Ages onions were enjoyed by peasants and aristocrats alike. Emperor Charlemagne ordered onions to be planted in his royal garden, they were written into the French feudal deeds, and strings of onions were even accepted as payment for the use of land. By that time, the three main vegetables of European cuisine were legumes, cabbage, and onions. In addition to serving as a food, onions were prescribed to alleviate headaches, snakebites, and hair loss. They were also used as wedding gifts.

Native American Indians had used wild onions raw and cooked, as a seasoning or as a vegetable, in syrups, as poultices, as an ingredient in dyes, and even as toys. On his second to sailing to Haiti in 1493 to 1494, Columbus brought varieties of cultivated onions to the New World. In 1620, the Pilgrims brought onions with them on the Mayflower. Pere Marquette, a French Jesuit missionary and explorer, avoided starvation in 1624 by consuming America’s native tree onions and nodding onions during his explorations from Green Bay, Wisconsin, to Lake Michigan’s southern shore. The city of Chicago, a region that grew wild onions in abundance, received its name from the Indian word that described the odor of onions. According to diaries of colonists, bulb onions were planted in Plymouth as soon as the Pilgrims could clear the land in 1648.

General Ulysses S. Grant, who headed the Union forces during the American Civil War, sent a note to the War Department that read, “I will not move my troops without onions.” He promptly received three cartloads. Grant also used onion juice to heal wounds.

American cowboys favored another native onion, the prairie onion, which they called skunk egg, probably due to its powerful odor.

Today, world onion consumption is estimated at 13.67 pounds per capita per year. Onions rank sixth among the world’s leading vegetable crops and third in the United States. As Americans search for healthy, tasty meals, they’re eating more onions–almost 18 pounds per person per year, which is 50% more than a decade ago. U.S. farmers plant approximately 125,000 acres of onions each year and produce about 6.2 billion pounds a year.

Onions are a very good source of vitamin C, fibermanganesevitamin B6, folate, and potassium. A 100-gram serving provides 40 calories, mostly as complex carbohydrate, with 1.4 grams of fiber. Like garlic, onions also have the enzyme alliinase, which is released when an onion is cut or crushed, and it causes your eyes to water. They also contain flavonoids, which are pigments that give vegetables their color. These compounds act as antioxidants, have a direct anti-tumor effect, and have immune-enhancing properties. Red and yellow onions are the richest dietary source of quercitin, a potent antioxidant flavonoid, which is found on and near the skin. Onions contain a large amount of sulfur and are especially good for the liver.

Onions can:

  1. Promote cardiovascular healthTo help keep your blood free of clots, and make the most of the health benefits of onions, eat them both raw and cooked. Onions can boost beneficial high-density lipoprotein (HDL or “good”) cholesterol, thin your blood, retard blood clotting, lower total blood cholesterol, lower triglycerides, and lower blood pressure. The vitamin B6 and folate in onions help prevent homocysteine build-up in your blood, reducing your risk for heart attack and stroke. Quercitin in onions can thin your blood, lower cholesterol, raise HDL cholesterol, ward off blood clots, and fight atherosclerosis. Saponins in onions lower blood cholesterol and decrease risk of cardiovascular disease. Campesterol in onions prevents the absorption of low-density lipoprotein (LDL or “bad”) cholesterol, balances blood cholesterol levels, and displays anti-inflammatory properties, which may make it beneficial for fighting cardiovascular diseases, among other health conditions. Isorhamnetin in red onions helps keep your heart healthy by preventing arteriosclerosis (hardening and loss of elasticity within the arteries), preventing high blood pressure, and protecting your heart’s cells against oxidative damage. Kaempferol in onions has cardioprotective activities. It seems to prevent arteriosclerosis by inhibiting the oxidation of LDL cholesterol and the formation of platelets in your blood. Allicin is a sulphur-containing compound that is formed when onions are crushed, chopped, or chewed. It can reduce cholesterol production in your liver, block platelet clot formation, and remove clots from your blood vessels, which helps decrease your overall risk of coronary artery disease (CAD), peripheral vascular diseases (PVD), and stroke. Kaempferol and allicin may also increase production of nitric oxide, a substance that acts as a natural dilator and relaxant of the blood vessels, which lowers your blood pressure.
  2. Promote lung health. Asthma sufferers may also benefit from a hearty dose of onions. A sulfur compound contained in onions can prevent the biochemical chain reaction that causes the bronchial muscles to spasm and leads to asthma attacks. They also relax bronchial muscles. Quercitin in onions can fight asthma, chronic bronchitis, and hay fever. 
  3. Fight free radicals. Onions are an excellent source of vitamin C, which helps protect cells from free radical damage. The manganese in onions is a co-factor for the antioxidant enzyme, superoxide dismutase. Saponins in onions neutralize free radicals to prevent disease. Isorhamnetin in red onions is a powerful antioxidant that protects your body’s cells from damaging free radicals. Kaempferol in onions is a strong antioxidant that helps to prevent oxidative damage of your cells, lipids, and DNA.
  4. Stabilize blood sugar. Onions are an excellent source of chromium, which enhances the actions of insulin. Onions have a significant blood sugar-lowering action. The active compound that seems to be responsible for lowering glucose works by competing with insulin for breakdown sites in the liver, thereby increasing the life span of insulin. Quercitin in onions can fight diabetes. Saponins in onions lower blood glucose responses. Isorhamnetin in red onions reduces the complications associated with diabetes (which include diabetic cataracts and high blood glucose levels). Kaempferol in onions has antidiabetic activities. 
  5. Fight pathogensOnions have potent antibacterial activity, destroying many disease-causing pathogens, including E. coli and salmonella. The vitamin C in onions supports your immune system. Quercitin in onions can fight bacterial and viral infections. Saponins in onions stimulate your immune system by increasing the production of antibodies, fight bacterial and fungal infections, prevent dental cavities, and increase the effectiveness of certain vaccines. Onions are especially useful for fighting the bacteria Streptococcus mutans and Streptococcus sobrinus, bacteria that are commonly involved in the production of tooth cavities. Onions also fight gum (periodontal) disease bacteria, including Porphyromonas gingivalis and Prevotella intermedia. The length of storage (for onion that has been chopped but not cooked) and duration of heat exposure (in this case involving exposure to steam for 10 full minutes) can affect some of onion’s antibacterial benefits. Kaempferol in onions has antimicrobial activities. Allicin in onions can inhibit bacterial, viral, and fungal infections in your digestive tract, including Helicobacter pylori, the bacteria responsible for gastric ulcers that increases your risk for stomach cancer.
  6. Fight cancer. Onions lower your risk of several cancers, including colorectal, laryngeal, and ovarian, esophageal, and cancers of the mouth. One way the antioxidants in onions can protect you against cancer is by reducing the DNA damage in cells caused by free radicals. The vitamin C in onions helps protect cells from free radical damage and lowers your cancer risk. Saponins in onions prevent cancer cells from growing and mutating. Onions are rich in organosulfur compounds shown to help prevent cancer. In fact, onion extract can destroy tumor cells and arrest tumor growth. The onion extract is also unusually nontoxic, since a dose as high as forty times that of the dose required to kill the tumor cells has no adverse effect on the host. Yellow and red onions contain quercetin, a powerful antioxidant that acts as an anti-cancer agent to block the formation of cancer cells. One and one-half to three and one-half ounces of raw onions eaten regularly contain enough quercetin to offer cancer protection. Quercitin is specifically linked to inhibiting human stomach cancer. It also deactivates the growth of estrogen-sensitive cells often found to cause breast cancer, and is thought to have diverse anti-cancer powers. Isorhamnetin in red onions prevents multiple types of cancer (including esophageal cancer, liver cancer, and lung cancer). Kaempferol in onions acts as a chemopreventive agent, which means that it inhibits the formation of cancer cells. Apigenin in onions is a very potent anti-cancer compound. Allyl sulfides in onions help reduce the risk of cancer by reducing the production of certain enzymes that convert cancer-causing precursors into their active form. Oxalic acid in onions is believed to be successful in fighting several kinds of tumor cells.
  7. Detoxify your bodyOnions contain a variety of organic sulfur compounds that provide health benefits. Sulfur-containing amino acids in onions, including methionine and cystine, are very good at detoxifying your body from heavy metals. They are able to latch on to mercury, cadmium, and lead and escort them out of your body. Vitamin C in onions is also excellent at detoxifying your body and is effective in removing lead, arsenic, and cadmium. 
  8. Support healthy bones and connective tissue. Manganese in onions facilitates the formation of bone. Folate helps prevent osteoporosis-related bone fractures. Potassium maintains the density and strength of your bones by decreasing urinary calcium loss. Phosphorus helps in the formation of bones and teeth. Saponins in onions protect against bone loss. Kaempferol in onions has anti-osteoporotic activities. Onions can help increase your bone density and may be of special benefit to menopausal women who are experiencing loss of bone density. Post-menopausal women may be able to lower their risk of hip fracture through daily consumption of onions. T

    he high sulfur content of onions may provide direct benefits to your connective tissue, because many of your connective tissue components require sulfur for their formation.

  9. Prevent chronic inflammation. Saponins in onions reduces inflammation. Campesterol in onions displays anti-inflammatory properties, which may make it beneficial for fighting arthritis and cardiovascular diseases, among other health conditions. Kaempferol in onions has anti-inflammatory activities. Onionin A, a unique sulfur molecule in onions, inhibits the activity of macrophages, specialized white blood cells that play a key role in your body’s immune defense system, and one of their defense activities involves the triggering of large-scale inflammatory responses. While macrophage activity is usually a good thing, inhibition of their activity can sometimes be critical in getting chronic inflammation under control. Onion’s antioxidants, including the flavonoid antioxidant, quercetin, also provide you with anti-inflammatory benefits. These antioxidants help prevent the oxidation of fatty acids in your body. When you have lower levels of oxidized fatty acids, your body produces fewer pro-inflammatory messaging molecules, and your level of inflammation is kept in check.

You can reap the health benefits of onions by eating just one medium onion, raw or cooked, each day.

Nutrients in 100 Grams Chopped Onions



Daily Value


24 µg


vitamin C

7.4 mg



1.7 g



0.1 mg


vitamin B6

0.1 mg



19 µg



146 mg



29 mg



9.3 g



0.046 mg



1.1 g






23 mg



10 mg



0.039 mg



0.027 mg



0.5 µg



0.2 mg



0.2 mg



0.1 mg


pantothenic acid

0.1 mg


vitamin K

0.4 µg



4 mg



0.1 g


vitamin E

0.02 mg


vitamin A

2 IU



0 mg



4 µg


1 µg

Onions are available year-round.  Those harvested in the spring and summer are available from March through August. They can be identified by their thin, lighter-colored skin. Typically higher in water content, spring and summer onions have a reduced shelf-life and are more susceptible to bruising. They range in flavor from sweet to mild, and are best to use in salads, sandwiches, and fresh, lightly-cooked, or grilled dishes. Some domestic and all imported onions with these traits are offered other times of the year.

Onions harvested during the fall and winter are available August through April. They’re easy to recognize by their multiple layers of thick, darker colored skin. Because they are lower in water content, they have a longer shelf-life. They range in flavor from mild to pungent and are best for savory dishes that require longer cooking times or more flavor.

Choose onions that are clean, firm, well shaped, have no opening at the neck, and feature crisp, dry outer skins with little to no scent. Avoid those with cuts, bruises, blemishes, soft spots, moisture, dark patches, or that are sprouting or have signs of mold. As conventionally grown onions are often irradiated to prevent them from sprouting, purchase organically grown varieties whenever possible to avoid onions that have undergone this process.

Onions should be stored in a well ventilated space at room temperature, away from heat and bright light. With the exception of green onions, do not refrigerate onions. 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, should keep for about a month if stored properly, since the compounds that confer their sharp taste help to preserve them. They will keep longer than those with a sweeter taste, such as white onions. Store onions away from potatoes, as they will absorb their moisture and ethylene gas, causing them to spoil more readily.

Store cut onions by placing them in a sealed container; use them 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 and much of their texture.

The flavonoids in onion tend to be more concentrated in the outer layers of the flesh. To maximize your health benefits, peel off as little of the fleshy, edible portion as possible when removing the onion’s outermost paper layer. Even a small amount of “overpeeling” can result in unwanted loss of flavonoids. For example, a red onion can lose about 20% of its quercetin and almost 75% of its anthocyanins if it is “overpeeled.”

The substance that causes your eyes to burn is a gas called lachrymatory factor (LF). LF is produced through activity of an enzyme named lachrymatory-factor synthase, although the alliinase enzyme must still be present in order for LF gas production to occur. Chill the onions for an hour or so before cutting; this practice can slow down the onion’s metabolism and thereby lessen the rate of LF gas production.   use a very sharp knife and always cut the onions while standing; that way your eyes will be as far away as possible. Consider cutting onions by an open window, and consider wearing glasses or goggles. Cut onions into 1/4-inch slices or dices to cook them evenly and quickly. Let them sit for at least 5 minutes to help the allicin form.

Watch How to Chop an Onion (although in my opinion, this chef removes too much of the outer skin):

Onions add flavor to an otherwise bland dish and turn an average meal into an elegant dinner.

When you simmer onions to make soup, their quercetin does not get degraded. It simply gets transferred into the water part of the soup. By using a low-heat method for preparing onion soup, you can preserve the health benefits of onion that are associated with this key flavonoid.

Here are some quick serving ideas:

  • Onions can be eaten on their own steamed, boiled, or roasted.
  • Sautéed chopped onions can be added to almost any vegetable dish to enhance its nutritional content and taste.
  • For an instant chili, heat together 1 medium chopped sautéed onion, with one can of kidney beans, one can of chunky tomato sauce, and season to taste with chili powder.
  • Chop 1 red onion, 2 medium tomatoes, 2 avocados and 1 jalapeno and combine together for an all-in-one guacamole salsa dip.
  • Place chunks of onion or small pearl onions on a skewer, either alone or with other vegetables, spritz lightly with olive oil, and grill for approximately 10 minutes.

This blog uses the latest nutritional data available from the USDA (United States Department of Agriculture), and the FDA (United States Food and Drug Administration), as well as nutritional data provided by food growers and manufacturers about their products. We believe the information on this blog to be accurate. However, we are not responsible for typographical or other errors. Nutrition information for recipes is calculated by Living Cookbook based on the ingredients in each recipe based on statistical averages. Nutrition may vary based on methods of preparation, origin and freshness of ingredients, and other factors.

This blog is not a substitute for the services of a trained health professional. Although we provide nutritional information, the information on this blog is for informational purposes only. No information offered by or through this blog shall be construed as or understood to be medical advice or care. None of the information on this blog should be used to diagnose or treat any health problem or disease. Consult with a health care provider before taking any product or using any information on this blog. Please discuss any concerns with your health care provider.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s