Onions: Health Benefits, Health Risks & Nutrition Facts

onions, types of onions, health, nutrition
There are three types of onions: yellow, red and white.
Credit: Africa Studio.

Turns out that onions are nothing to cry over — these flavorful bulbs are packed with nutrients. They are excellent sources of vitamin C, fiber, folic acid, antioxidants and other important flavonoids and phytochemicals.

One particularly valuable flavonoid in onions is quercetin, which is linked to preventing cancer, reducing the symptoms of bladder infections, promoting prostate health, and many other benefits. Other important phytochemicals in onions are disulfides, trisulfides, cepaene and vinyl dithiins. They all are helpful in maintaining good health and have anticancer and antimicrobial properties.

Partly because of their use in cooking around the world, onions are among the most significant sources of antioxidants in the human diet. Their high levels of antioxidants give onions their distinctive sweetness and aroma. These antioxidants and flavonoids may help promote heart health, reduce inflammation, and reduce the risk of cancer, in addition to a load of other good things.

Onions are low in calories (45 per serving), very low in sodium, and contain no fat or cholesterol. Onions are healthy whether they’re raw or cooked, though raw onions have higher levels of organic sulfur compounds that provide many benefits. The beneficial flavonoid quercetin, however, does not degenerate when onions are simmered to make soup. It transfers to the water instead, especially when cooked on a low heat.

The flavonoids in onions are found in the highest concentration in the outer layers of the flesh, so you’ll want to be careful to remove as little of the edible part of the onion as possible when peeling it.

Here are the nutrition facts for avocados, according to the U.S. Food and Drug Administration, which regulates food labeling through the National Labeling and Education Act:


Nutrition Facts

Serving size:
1 medium onion
(5.3 oz / 148 g)

Calories 45
  Calories from Fat 0

*Percent Daily Values (%DV)
are based on a 2,000 calorie diet.

Amt per Serving %DV*   Amt per Serving %DV*  
Total Fat 0g 0%   Total Carbohydrate 11g 4%
Cholesterol 0mg 0%     Dietary Fiber 3g 12%
Sodium 5mg 0%      Sugars 9g  
Potassium 190mg 5%   Protein 1g  
Vitamin A 0%   Calcium 4%
Vitamin C 20%   Iron 4%


Health benefits of onions

Heart health

Onions encourage a healthy heart in many ways. The sulfur in onions can help lower high blood pressure, lower bad cholesterol, and increase good cholesterol. It can also help to prevent blood clots, stroke, and your arteries from hardening. The sulfur acts as a natural blood thinner and prevents blood platelets from aggregating. When platelets cluster, the risk for heart attack or stroke increases significantly, so onions’ blood-thinning properties can be a powerful aid against these heart problems. Raw onions are especially beneficial in this regard. The quercetin in onions can also help prevent plaque buildup in the arteries, which reduces the risk of heart attack and stroke.


Onions have been used to reduce inflammation for centuries. Onions’ sulfurs are effective anti-inflammatory agents. For this reason, onions are often considered a home remedy for asthmatic symptoms. They can even reduce inflammation in blood vessels, which reduces the risk of heart disease. The quercetin in onions can help with arthritis pain by easing swelling and joint stiffness.

Immune system

Onions can promote a strong immune system by eliminating free radicals, improving the effectiveness of vitamin C in your body, and improving the absorption of minerals through probiotics, which are promoted by the fiber in onions. The quercetin in onions also reduces allergic reactions by stopping your body from producing histamines, which are what make you sneeze, cry, and itch if you’re having an allergic reaction.


Onions are high in quercetin, a powerful anti-cancer agent. In lower concentrations, quercetin helps prevent cancer cells from growing by killing free radicals. In higher concentrations, quercetin becomes toxic to cancer cells.

One recent study from the Netherlands showed that people who ate onions absorbed twice as much quercetin as those who drank tea, and more than three times as much quercetin as those who ate apples, which are other high-quercetin sources. Red onions are especially high in quercetin. Shallots and yellow onions are also good options. White onions contain the least amount of quercetin and other antioxidants.


Onions have amino acids that are rich in organic sulfur. They initiate detoxification by forming the basis for glutathione, helps the liver process toxins.


The fiber in onions promotes good digestion and helps keep you regular. Additionally, onions contain a special type of soluble fiber called fructan, which promotes good bacteria growth in your intestines, which helps keeps them healthy and ward off infections. The phytochemicals in onions that scavenge free radicals also reduces your risk of developing gastric ulcers.

Regulating blood sugar

The chromium in onions assists in regulating blood sugar. The sulfur in onions helps lower blood sugar by triggering increased insulin production.

Bone density in older women

A 2009 study found that daily consumption of onions improves bone density in women who are going through or have finished menopause. Women who ate onions frequently had a 20 percent lower risk of hip fracture than those who never ate onions.

Health risks

While not especially serious, eating onions can cause problems for some people. The fructose in onions may cause gas and bloating. Onions, especially if consumed raw, can worsen heartburn in people who suffer from chronic heartburn or gastric reflux disease. 

Eating a large amount of green onions or rapidly increasing your consumption of green onions may interfere with blood thinning drugs. Green onions contain a high amount of vitamin K, which can decrease blood thinner functioning.

It is also possible to have a food intolerance or allergy to onions. People with onion allergies may experience red, itchy eyes and rashes if an onion comes into contact with the skin. People with a food intolerance to onions may experience nausea, vomiting, and other gastric discomfort.

Onion history

According to the National Onion Association:

Onions probably originated in central Asia, in modern-day Iran and Pakistan. Prehistoric people probably ate wild onions long before farming was invented. Onions may have been among the earliest cultivated crops.

Onions also grew in Chinese gardens as early as 5,000 years ago, and they are referred to in the oldest Vedic writings from India. As early as the sixth century B.C., a medical treatise, the Charaka Sanhita celebrates the onion as medicine, a diuretic, good for digestion, the heart, the eyes, and the joints.

A Sumerian text dated to about 2500 B.C. tells of someone plowing over the governor's onion patch.

In Egypt, onions were planted as far back as 3500 B.C. They were considered to be objects of worship, and symbolized eternity because of the circle-within-a-circle structure. Paintings of onion appear on the inner walls of pyramids and other tombs.

Onions were buried with mummies. Some Egyptologists theorize that onions may have been used because it was believed that their strong scent and/or magical powers would prompt the dead to breathe again.

Onions are mentioned in the Bible. In Numbers 11:5, the children of Israel lament the meager desert diet enforced by the Exodus: "We remember the fish, which we did eat in Egypt freely, the cucumbers and the melons and the leeks and the onions and the garlic."

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.

The Romans ate onions regularly. Pedanius Dioscorides, a Roman physician of Greek origin in first century A.D., noted several medicinal uses of onions.

Pliny the Elder catalogued Roman beliefs that onions could cure poor vision, induce sleep, and heal mouth sores, dog bites, toothaches, dysentery and lumbago. Pliny wrote of Pompeii's onions and cabbages, and excavators of the doomed city found gardens where, just as Pliny had said, onions had grown. The bulbs had left behind cavities in the ground.

By the Middle Ages, the three main vegetables of European cuisine were beans, cabbage and onions. Onions were prescribed to alleviate headaches, snakebites and hair loss. They were also used as rent payments and wedding gifts.

The Pilgrims brought onions with them on the Mayflower. However, they found that Native Americans were already using wild onions in a variety of ways: eating them raw or cooked, as a seasoning or as a vegetable. Onions were also used in syrups, as poultices, as an ingredient in dyes, and even as toys.

Onion facts

Slicing onions makes you cry because when you cut into it, the onion produces a sulfur-based gas. The gas reacts with the water in your eyes and forms sulfuric acid. To rid your eyes of this fiery irritant, your tear ducts work overtime. For no more (or fewer) tears, try moving your face farther away from the onion so the gas disperses before reaching your eyes.

Another suggestion for reducing tears is to first chill the onions for 30 minutes. Then, cut off the top and peel the outer layers leaving the root end intact.

Bulb onions are yellow, red or white. In the United States, about 87 percent of the commercial onion crop is yellow onions, 8 percent is red onions and 5 percent is white onions.

Onions range in size from less than 1 inch to more than 4.5 inches in diameter. The most common sizes sold in U.S. markets are 2 to 3 3/4 inches.

Scallions, or green onions, are actually immature yellow, red or white onions, harvested before the bulb begins to form. “Spring onions” and “salad onions” are other aliases for immature onions.

A scallion is nota shallot. This misnomer probably occurs because “échalion” is another name for the shallot, derived from the French échalote. Shallots have a distinctive taste, but the flavor is closer to that of mature onions than to that of scallions.

The largest onion ever grown weighed 10 pounds 14 ounces (about 5 kilograms), according to the Guinness Book of World Records.

U.S. farmers plant about 125,000 acres of onions each year and produce about 6.2 billion pounds a year. The top onion-producing areas are Washington state, Idaho-Eastern Oregon and California.

The Ieading onion production countries are China, India, United States, Turkey and Pakistan.

The average American eats 20 pounds (9 kg) of onions per year.

To avoid "onion breath," eat a sprig of parsley, or rinse your mouth with equal parts lemon juice and water, or chew a citrus peel.

Onion quotes

"I will not move my army without onions!"
— Ulysses S. Grant

"It's hard to imagine civilization without onions."
— Julia Child

"Onion skins very thin
Mild winter coming in.
Onion skins very tough,
Coming winter very rough."

— old English rhyme

"Mine eyes smell onions: I shall weep anon."
— 'All's Well that Ends Well' by William Shakespeare

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