Onions: Onion Nutrition, Benefits, Recipes, Side Effects - Dr. Axe

Fact Checked

This Dr. Axe content is medically reviewed or fact checked to ensure factually accurate information.

With strict editorial sourcing guidelines, we only link to academic research institutions, reputable media sites and, when research is available, medically peer-reviewed studies. Note that the numbers in parentheses (1, 2, etc.) are clickable links to these studies.

The information in our articles is NOT intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice.

This article is based on scientific evidence, written by experts and fact checked by our trained editorial staff. Note that the numbers in parentheses (1, 2, etc.) are clickable links to medically peer-reviewed studies.

Our team includes licensed nutritionists and dietitians, certified health education specialists, as well as certified strength and conditioning specialists, personal trainers and corrective exercise specialists. Our team aims to be not only thorough with its research, but also objective and unbiased.

The information in our articles is NOT intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice.

Onions Nutrition Benefits the Heart, Bones & More (+ Onion Recipes)


Onions - Dr. Axe

Records show that various types of onions have been used worldwide as a valuable medicinal and food source for thousands of years. Many ancient populations believed that onion nutrition had a beneficial effect on disease treatment and immunity, which is why this vegetable has long been encouraged as part of a healing diet.

Why is eating onions good for you?

Studies suggest that that onion health benefits, such as enhanced immunity and cancer protection, are due to onion’s many antioxidants. These include flavonoids like quercetin and anthocyanins, the same type of protective compounds founds in berries, cherries and eggplant — plus organosulfides and nutrients like vitamin C.

What Are Onions?

Onions (species name Allium cepa L.) are a member of the Amaryllidaceae plant family, which also includes other flavorful allium vegetables like garlic and leeks. Allium vegetables contain therapeutic oils that hold sulfur compounds (cysteine sulfoxides).

These are partially responsible for their signature smell and taste. They’re also responsible for many of the health benefits of onion nutrition, especially when it comes to naturally treating cancer.

Are onions vegetables?

Yes, according to the University of California Department of Plant Sciences, a vegetable is any edible portion of a plant, and vegetables are usually grouped according to the portion of the plant that is eaten, such as leaves or roots. In the case of the onion, the bulb is eaten, making it a vegetable.


Amaryllidaceae is another name for the onion family of vegetables, which includes onion varieties like:

  • white, yellow and red onions
  • shallots and scallions (green onions)
  • pearl onions
  • Spanish onions
  • Vidalia onions
  • leeks
  • chives
  • and others

Which type of onion is healthiest? 

According to research looking at onion nutrition, yellow onion nutrition is especially impressive because this type contains the most quercetin and also the most sulfur compounds. Red onions (or purple onions) are higher in other protective antioxidants (as indicated by their color).

However, studies show that all onions are beneficial in their own ways, particularly due to their sulfur-containing compounds.

Many people enjoy sweet onion varieties best, like Vidalia onions and shallots, because they tend to have a milder taste and can even be eaten raw, but compared to white and red onions, these usually have a lower percentage of beneficial compounds.

Sweeter onions are left in the soil longer before being harvested so more of their carbohydrates have a chance to turn to sugars, hence their sweeter taste.

In general, the longer onions are left in the ground, the sweeter they taste but the lower phytonutrient count they have. Usually, the more potent the smell and taste of an onion, the more nutrients are present (and therefore the onion is more likely to make you tear).

What are scallions (also called green onions or spring onions), and are they healthier than white or yellow onions?

Scallions are young onions that are harvested when their tops are green, and they have underdeveloped bulbs. They have a mild flavor and can be consumed raw, including the stem, bulb and leaves.

They are high in several important antioxidants, including flavonoid phenolic compounds — such as carotenes, zeaxanthin and lutein — plus nutrients like vitamin K, vitamin C and fiber.

What about shallots vs. onions?

Shallots are a small variety of onion that have a white, light brown or red skin and a mild flavor. They contain many antioxidants, including sulfoxides, which give them antibiotic, antidiabetic and fibrinolytic properties.

Shallots can help reduce oxidative damage and fight various health problems, like infections, high blood sugar levels/insulin resistance, blood clots and high LDL cholesterol levels.

Related: Allicin: The Beneficial Compound that Makes Garlic So Healthy

Onions are among the world’s oldest cultivated plants. Although there’s no conclusive evidence as to where they first appeared, their history goes back about 5,000 years to parts of the Middle East and Southwestern Asia, including Iran and West Pakistan.

They are believed to be one of the earliest cultivated crops because they were less perishable than other foods of the time, last a long time, are transportable, can easily be grown year-round, and grow well in different types of climates and soils. They can also be dried and preserved, which has made them a valuable source of nutrients during times of famine.

Some records show that onions grew in parts of China, India and Egypt around the time of 3500 B.C. In Egypt, they were even considered to be an object of worship and symbolized eternity because of the onion’s “circle-within-a-circle” structure.

Paintings of the vegetable can even be found within the inner walls of the ancient Egyptian pyramids and tombs. Onions were also eaten by the Israelites and mentioned as one of the Bible foods, along with cucumbers, melons, leeks and garlic.

Ever wonder why your eyes water when cutting an onion? It’s because cutting onions punctures their cell membranes that store sulfur compounds and flavonoids.

While it might be inconvenient to tear up while cooking, as you can see it’s a small price to pay for the very impressive roles that these compounds hold when it comes to disease prevention.

Nutrition Facts

According to the USDA, one cup (approximately 160 grams) of raw, chopped onion nutrition contains about:

  • 64 calories
  • 14.9 grams carbohydrates
  • 2 grams protein
  • 0.2 grams fat
  • 3 grams fiber
  • 11.8 milligrams vitamin C (20 percent DV)
  • 0.2 milligrams vitamin B6 (10 percent DV)
  • 0.2 milligrams manganese (10 percent DV)
  • 30.4 micrograms folate (8 percent DV)
  • 234 milligrams potassium (7 percent DV)
  • 46 milligrams phosphorus (5 percent DV)
  • 0.1 milligrams thiamine (5 percent DV)

In addition, onion nutrition contains small amounts of vitamin A, vitamin K, niacin, pantothenic acid, choline, betaine, calcium, iron, magnesium, zinc, copper and selenium.

Health Benefits

1. May Help Fight Cancer

According to many clinical studies looking at onion nutrition benefits, this vegetable can help reduce the risk of developing colon, ovarian and mouth cancers through its rich supply of antioxidants that prevent cell damage.

Onion’s sulfur compounds have been found in studies to prevent the growth of tumors and cancer development by protecting cells from mutation and inducing apoptosis. They seem to be especially protective against cancers affecting the gastrointestinal tract, according to research published in 2016 by the National Cancer Institute.

What happens if you eat onions every day? Even consuming onion just several times per week has been linked to enhanced cancer protection. Of course, the more you consume, the more you’ll benefit.

For example, large studies from Southern European populations published in the American Journal of Clinical Nutrition show an inverse association between the frequency of consuming onions and other allium vegetables and the risk of developing several common cancers.

At least 25 different flavonoid compounds have been identified across all onion varieties. Studies suggest that quercetin benefits include lowering the effects of histamines on the immune system.

In fact, quercetin is considered an antihistamine phytonutrient that’s often found in allergy products. Anthocyanins, the same type of antioxidants found in red berries, are responsible for giving red onion its deep color and have been linked to anti-carcinogen and anti-tumor effects.

Studies show that another form of onion’s flavonoids is alkenyl cysteine sulphoxide, a sulfur compound that has been reported to have a range of health benefits, including anti-carcinogenic properties, anti-platelet activity, anti-thrombotic activity, anti-asthmatic and antibiotic effects.

2. Protects Heart Health

Why are onions good for your heart? They have fibrinolytic benefits, meaning they provide cardiovascular protection by reducing the risk of blood clot formation.

Additionally, they can protect against “bad” LDL cholesterol. They do this by limiting the activity of harmful free radicals within blood vessels, therefore lowering oxidative stress and improving blood circulation and blood pressure levels.

A 2017 study found evidence that onions can act as “functional ingredients with bioactive lipid mediator potential and impact on inflammation, oxidative stress and organ dysfunction.” Onion-derived phenolic compounds, including flavonols and organosulfur compounds (especially thiosulfinates), seem to play a positive role in balancing cholesterol via several metabolic pathways, such as those involving arachidonic acid.

3. Helps Maintain Strong Bones

What are the health benefits of onions in terms of bone health? They support bone health because they can help foster greater bone mineral density, which lowers the risk for bone fractures. One study done by the Department of Family Medicine at the University of South Carolina found that bone density increased in women as the frequency of onion consumption increased.

Women who consumed onions once a day or more had an overall bone density that was 5 percent greater than individuals who consumed them once a month or less. Researchers concluded that women who consume this vegetable most frequently may decrease their risk of hip fractures by more than 20 percent versus those who never consume onion.

One possible mechanism responsible for the bone-building benefits of onion nutrition might be its GPCS substances (gamma-L-glutamyl-trans-S-1-propenyl-L-cysteine sulfoxides). These help inhibit the breakdown of bone and prevent osteoporosis and reverse osteopenia or corticosteroid-induced bone loss.

4. Can Help Prevent or Manage Diabetes

There’s good news for those following a low-carb diet for various health reasons, such as to control blood sugar levels and diabetes. There are relatively few carbs in onions, yet many phytonutrients that have anti-inflammatory effects.

A large meta-analysis of animal research done by the Plant Resources Research Institute in Korea found that onion extract can help fight diabetes because onion intake may be effective for lowering plasma glucose concentrations and body weight. Onions are an effective, natural way to control the level of blood sugar released into the bloodstream and prevent insulin resistance.

Onion nutrition research also shows that onions supply chromium, which is beneficial for controlling blood glucose and may be beneficial for preventing diabetes.

5. Lowers Risk of Arthritis and Asthma

Because onions as a great anti-inflammatory food, they’re one of the best vegetable choices if you suffer from painful inflammatory diseases like arthritis or asthma. According to the National Arthritis Foundation, quercetin found in onions may be especially beneficial for arthritis sufferers because it helps inhibit inflammation-causing leukotrienes, prostaglandins and histamines that worsen pain and swelling.

6. Defends Against Respiratory Infections

The next time you’re suffering from a cold or respiratory illness, try consuming more onions as a natural way to beat that cold. Experts believe that certain onion nutrition phytonutrients can increase immune defense; fight inflammation; reduce mucus in the nasal passages, lungs and respiratory system; and help you feel better quicker.

Onions also have natural antibacterial properties, making them beneficial for fighting infections.

7. May Help Improve Fertility

Antioxidants have a big impact on sperm health parameters, so onions may be one natural way to improve fertility. When researchers from Azad University in Iran investigated the effects of onions on fertility of rats, they found that total testosterone significantly increased, as did sperm concentration, viability and mobility in the rats who received high levels of onions over the course of 20 days.

8. May Help Improve Your Sleep

Do onions help you sleep? Many people swear that smelling an onion before bed helps them fall asleep faster. While more research is needed to confirm this, the current evidence is promising.

In a double-blind, placebo-controlled crossover study published in Food Science and Biotechnology, researchers examined concentrated onion extract’s ability to help with sleep. The study involved 30 men and women who were displeased with their sleep consuming an onion extract with concentrated  cysteine sulfoxides for five days.

Researchers concluded “that onion extract containing concentrated cysteine sulfoxides alleviates stress, improves the quality of sleep and promotes smooth transition into sleep.”

9. Helps Alleviate Scars and Keloids

Several clinical studies have found onions to be a useful treatment for keloids. This is probably because of the anti-inflammatory and antioxidant effects of quercetin. Researchers have studied the use of onion extract gel applied to the skin, including under dressings and compresses.

Although onion extract gel has been used effectively for keloid prevention and treatment on its own, other studies combined it with traditional medications and found it boosted reduction of keloids.

The study where the gel alone was effective included Asian women with scarring from cesarean section births. They applied a 12 percent topical onion extract gel three times a day for 12 weeks and had smaller, less noticeable scars than those who applied a placebo gel.

You can try a similar approach at home by cutting an onion into small pieces, then pressing down on them with a clean towel to squeeze out the juice.

Dab the juice on the keloid or scar, or place just the wet towel on the keloid. Let it dry. Rinse your skin. Repeat up to four times per day.

Risks, Side Effects and Interactions

Are onions toxic to humans?

A myth that originated in the early 1900s is that cut onions are toxic and poisonous when stored in the refrigerator due to their tendency to absorb bacteria. However, studies show that this isn’t true. In fact, onions have antibacterial properties.

Cut onions are known to kill or inhibit the growth of several types of microorganisms, including some that can trigger food poisoning, so they are not only safe to eat, but protective and beneficial.

Onions do have a tendency to cause reactions in people who suffer from poor digestion of FODMAP foods and also from conditions like heartburn or acid reflux. If you experience onion side effects such as bloating, gas or abdominal pain, you might have to try eliminating them for a period of time to see if the symptoms clear up.

Some people can digest small amounts of cooked onions better than large quantities, or raw onions, so it might take some trial and error. If white, red or yellow onions bother you, try having leeks, scallions and chives instead, which tend to cause less digestive issues but also add flavor and nutrients to recipes.

How to Buy, Prepare and Store

Onions are also available in various fresh/whole and processed forms, including:

  • Boiled and pickled onions packed in cans or jars, which are used a condiments
  • Frozen, chopped onions
  • Bottled onion juice, which is sold for flavoring
  • Dehydrated onion powder products (like granulated, ground, minced, chopped and sliced forms)

Reports show that onions are actually one of the vegetables least contaminated with pesticide chemicals. In fact, some sources say that they’re the very lowest vegetable in terms of storing pesticide residues.

Therefore, buying organic onions isn’t always necessary if you’re looking to eat healthy on a budget. You can save your money to spend on other produce instead that tends to be sprayed win higher levels of chemicals (like spinach, apples and berries) — though it’s never a bad idea to buy organic foods.

Onions are known to last a long time, especially for a vegetable. You can store onions on your countertop for just about a month before they start to go bad so there’s no downside to stocking up on them when you’re at the grocery store.

Here’s something else somewhat unique to onions in regard to their storage: When they’re left near potatoes, they absorb ethylene gas that potatoes give off and tend to spoil at a much quicker rate. Thus, it’s always best to keep onions and potatoes separate — but keep both unrefrigerated.

You don’t want to refrigerate uncut onions because this actually makes them spoil sooner. However, once you do cut open onions, keep them in the refrigerator, and use them as soon as possible in order to make sure all of their beneficial nutrients are still intact.

Because they have a strong odor and smell, keep them separate from all other foods in a tightly sealed container so your whole refrigerator or freezer doesn’t wind up absorbing the onion smell and taste.

Preparing Onions

Different onions are best in different types of recipes. For example, red onions and shallots are usually the kind eaten raw, while white and yellow onions are preferred when cooked.

No matter the type you choose, keep in mind that a high percentage of valuable phytonutrients — which are the keys to the many onion nutrition benefits described above — are stored toward the surface of the vegetable right under its thin, paper-like outer peel. To maximize the benefits of onions, only peel off the onion’s outermost layer, and consume the rest of the fleshy, moist parts.

Studies show when you cut onions open, if you leave them exposed to air for about 10 minutes their phytonutrient content actually increases and becomes more absorbable. If you have the time when cooking, chop your onions and leave them on a cutting board for several minutes before adding them to recipes.

How to Cook (Plus Onion Recipes)

There are dozens of ways to use onions in healthy recipes every day. You can add them to eggs, throw them in soup, try raw red onions on salads, add some to quinoa recipes or brown rice pilaf dishes, use them to make sauces in order to lend flavor to fish or other proteins, and many other ways too.

You can bring out the naturally sweet flavor of onions, as well as the absorbability of onion’s nutrients, by briefly cooking them. The thinner you slice onions, the more quickly they will cook.

The longer you cook them, the more their sugars are released and the sweeter they taste.

Try sautéing them in some grass-fed buttercoconut oil or olive oil briefly. You can also submerge and boil them in stock, which will absorb their flavors.

Compared to many other vegetables, onion’s phytonutrients are usually well-preserved during cooking and aren’t considered very delicate compounds.

Onion Recipes

Onions are extremely versatile in recipes. In fact, they’re used in just about every culture’s cuisine in the world in one way or another, whether French, Chinese, Mexican or Indian.

Try some of these onion recipes to add antioxidants and protective phytonutrients to your diet, along with plenty of low-calorie, natural flavor.

Can You Juice Onions?

Juicing onions may sound unpleasant, but some people swear that the taste isn’t too off-putting and worth it when you consider the many benefits of onion juice. Drinking even small amounts of onion juice can be a good way to obtain valuable nutrients that are most concentrated in raw, rather than cooked, onions.

If you’re feeling brave you can add a peeled and quartered onion to juices or even smoothies, preferably with a teaspoon of raw honey or some apples or carrots to help improve the taste.

Final Thoughts

  • Onions (species name Allium cepa L.) are a member of the Amaryllidaceae plant family, which also includes other flavorful allium vegetables like garlic and leeks. There are many types, such as yellow, white, red, pearl, Spanish and Vidalia onions, plus scallions, shallots and chives.
  • Onion nutrition health benefits include providing antioxidants that fight inflammation, cancer protection, improved heart health, and protection against infections, asthma, arthritis symptoms and more.
  • This vegetable contains flavonoids like quercetin and anthocyanins, the same type of protective compounds founds in berries, cherries and eggplant, plus organosulfides and nutrients like vitamin C.
  • An onion can be eaten raw or cooked. Different varieties are best in different types of recipes.
  • Red onions and shallots are usually the kind eaten raw, while white and yellow onions are preferred when cooked.

More Nutrition