In this article:
- Onions are nutritional powerhouses that contain generous reserves of vitamins A, B complex, and C, as well as magnesium, folate, and potassium.
- Multiple health benefits are attributed to onions, which range from scar healing, lowering elevated blood sugar, and preserving heart health to fighting obesity.
- Onions, when cut, release sulfur-containing fumes that cause your eyes to redden and water on exposure. These fumes are also responsible for the strong onion odor that lingers on your breath.
- The oral and topical use of onions can trigger side effects and allergic reactions in some people, typically in the form of skin irritation, tearing of the eyes, and stomach distress.
- Onion juice is recognized as a hair tonic, which can help fight hair thinning by strengthening the existing strands and promoting the growth of new ones, although these claims still need to be corroborated by scientific research.
- If you freeze onions before chopping them, they are unlikely to irritate your eyes.
Onions are a staple crop and are used in cuisines throughout the world. They have been popular for centuries. There are over 300 varieties of onions, and they come in different sizes, shapes, colors, tastes, and smells.
Onions (Allium cepa) is the most widely grown species in the Allium genus. An estimated 46.7 tons of onions is grown worldwide. (1)
They are the third most consumed vegetable in America, falling behind potatoes, tomatoes, and corn. Most onions are consumed fresh. (2)
Onions grow wild in many regions throughout the world, and they may be one of the earliest cultivated crops due to their long shelf-life and ease of transport. They also grow well in a variety of soils and climates, adding to their popularity.
Onions have anti-allergen, cancer-fighting, antioxidant, and anti-inflammatory properties. They are rich in vitamins A, B, and C and also contain folate, magnesium, and potassium.
Onions are particularly rich in quercetin, an antioxidant flavonoid. (3) One cup of chopped raw onion contains 64 calories, 15 g of carbohydrate, of which 2.7 g is fiber; almost 2 g of protein; and no fat.
It also contains one-fifth of your daily needs for vitamin C, 10% of your daily requirement for B6, and 10% of your daily manganese needs. One cup of raw onion also contains 5% of your daily requirement for phosphorus and 7% of your potassium needs. (3)
Types of Onions
Onions come in many different sizes, shapes, and colors:
- Brown or yellow onions: These bulbs have brown skin and creamy flesh. They have a strong flavor and a pungent aroma, which make them very popular in cooking.
- Red onions: These bulbs have a red-purple skin and white flesh with a red outer layer. They tend to be medium or large. They have a sweet, mild taste and are often enjoyed raw.
- White onions: These bulbs are harvested before completely ripe and only kept for a short period of time. They are not as strongly flavored nor as pungent as brown or yellow onions. They can be used raw or cooked.
- Green onions: These are also called spring onions, scallions, or salad onions. These are actually immature onions that are harvest before grown. They have tiny white bulbs and green tops. The roots are typically removed, and the rest of the onion is consumed.
Health Benefits of Onions
Onions not only provide flavor and aroma to dishes, but they also offer many benefits to health.
1. Helps to Remove Scars
Applying onion extract topically may help improve the appearance, pain, and itching of different types of scars.
Studies have shown that onion extract is effective at improving the appearance of scars, but more research is needed to understand the way it works as well as its proper usage and dosage.
2. Helps to Regulate Blood Sugar
Some studies have shown that onions and onion extracts may be helpful for patients with diabetes, but more research is needed to understand the proper usage, dosage, and mechanism of onion against diabetes.
3. May Promote Cardiovascular Health
Many people believe that onions can help improve heart health, and recent research has shown there might be something to this claim.
Research done on animals has demonstrated the multiple ways in which quercetin may improve blood pressure, but there have yet to be many human trials. (11)
Some studies have shown that onions and onion extracts may be helpful for cardiovascular health, but these studies have mainly been done on animals. More research is needed to understand the proper usage, dosage, and mechanism of onion for the improvement of heart health.
4. Helps to Manage Obesity
The properties of quercetin, a powerful antioxidant found in onions, are still being studied and understood, but some studies suggest that it may help with obesity.
One study done on obese adults in Korea found that onion peel extract may help reduce overall weight and lower body fat percentage. (14)
Some research on animal models suggests that quercetin and onion peel extracts may help reduce obesity, but more studies are needed on humans to understand its effectiveness, safety, proper usage, and dosage.
5. Helps Improve Bone Density
There is not much clinical evidence and research on the topic of onions and bone density.
Other Possible Benefits of Onions
Some studies revealed a positive correlation between onions and these health conditions:
How to Buy and Store Onions
Look for onions that are clean, have no opening at the neck of the bulb, are well-shaped without blemish, and have dry outer skins. Avoid any signs of mold or sprouting.
Keep onions in a dry space at room temperature, away from light and heat. Do not refrigerate onions, except for green onions. Keep onions in a perforated container that allows air to circulate around them.
Chopped onions can be kept in an airtight container inside the refrigerator. Use within a few days.
Onions are enjoyed raw, broiled, baked, sautéed, grilled, boiled, steamed, fried, and pickled. They can be used in soups, stews, and a variety of dishes with other vegetables and meats.
Onion oil is also used for culinary purposes. The outermost layers of onions have the highest concentration of flavonoids. Peel off as few layers as possible, all the while totally removing the papery layer.
Generally, onions are considered to be safe, and side effects are rare.
Those that consume large quantities of onions may experience heartburn or other gastrointestinal distress. Exposure to a cut onion may cause involuntary tearing.
People with an intolerance to onion can usually take a small amount of cooked onions. Raw onions may cause a true allergic reaction in some people. People with an allergy to onions may also experience allergies to other members of the Allium genus, such as garlic and shallots.
Onions and garlic are used in many prepared and packaged foods and may not always be listed on the label individually, but rather included in “spices.” It is also used in many restaurant dishes. Read ingredient lists carefully and alert staff to your allergy.
- Aspirin: If you have an allergic reaction to onions, aspirin may increase your sensitivity to this vegetable.
- Medications for diabetes: If you are taking diabetic medications, taking high doses of onion extracts or supplements may lower your blood sugar to dangerous levels.
- Anticoagulants: Onions may slow blood clotting. If you are taking an anticoagulant or blood thinner, taking onion extracts or supplements may increase your risk of bruising or bleeding.
Are shallots a type of onion?
Shallots are part of the Allium genus and taste very similar to an onion, but look more like garlic cloves. They are formed in clusters of cloves, and their papery skin is usually reddish-brown. They tend to have a similar aroma to onions, but are much milder and sweeter in flavor.
Do onions have adverse impacts on pregnancy?
Consuming onions in cooked foods is fine, although, for some women, it may exacerbate heartburn. Due to a lack of evidence regarding the safety, it is recommended to avoid consuming onion supplements during pregnancy or breastfeeding.
How do you cut an onion without getting teary eyes?
Using a very sharp knife and cutting while standing can reduce crying while cutting onions.
Standing while cutting onions increases the distance from the onions and helps reduce the amount of particulates that can get in the air and irritate your eyes. Cutting onions by an open window may also help.
Are onion supplements safe during surgery?
Onions may slow blood clotting and can lower blood sugar, so it is best to stop taking onion supplements at least 2 weeks before surgery.
Can onions be eaten on a keto diet?
Onions do contain some carbohydrates. So, if you are following a keto diet, measure how much onions you consume to avoid going over the carbohydrate limit.
Are raw onions better than cooked onions?
Both raw and cooked onions contain healthy compounds. Raw onions do contain more sulfur, which may be beneficial to some health conditions. But generally speaking, both raw and cooked onions contribute to your overall health.
Recipes Using Onions
1. Marinated Roasted Onions
- 4 large yellow onions
- 1 cup water
- 1 cup red wine vinegar
- 2 tablespoons brown sugar
- 2 teaspoons rosemary, chopped, divided
- 3½ teaspoons salt
- ½ teaspoon pepper
- ¼ teaspoon red pepper flakes, optional
- 4 tablespoons butter or oil
- In small bowl or jar, combine water, vinegar, sugar, 1 teaspoon rosemary, salt, pepper, and red pepper flakes, if using. Whisk together or screw the lid on and shake.
- Cut the onions horizontally in half, removing the top and root end. Place them larger side down in a large glass baking dish.
- Pour the vinegar mixture over the top and ensure that some gets under the onions. Cover the dish. Marinate overnight in the refrigerator.
- Preheat oven to 400°F. Lay the onion halves on a baking tray, with the wide-cut side facing up. Top each onion half with a bit of butter or oil and a sprinkle of the remaining rosemary.
- Roast uncovered for 1 hour, basting a few times while roasting.
- Take the onions out of the oven, and spoon the sauce over the onions.
- Garnish with fresh parsley and serve.
2. Tennessee Onions
- 2-3 Vidalia or sweet onions
- 4 tablespoons butter
- Garlic salt, to taste
- Pepper, to taste
- 1 cup shredded cheddar cheese
- 1 cup shredded mozzarella cheese
- ½ cup Parmesan cheese
- Fresh oregano, to taste
- Spray a 9×13-inch baking dish with cooking spray. Preheat oven to 350°F.
- Slice the Vidalia onions into ½-inch slices and separate.
- Lay the rings in the baking dish. Sprinkle with garlic salt and pepper.
- Cut the butter into pats and place them randomly on top of the onions.
- Sprinkle the cheeses on top of the onions.
- Bake without any cover for around 30 minutes or until bubbly.
- Take the onion rings out of the oven and allow them to cool for a few minutes before serving.
Onions have been used around the globe for centuries. They are popular both as mature and immature bulbs, can be kept for long periods of time, and can withstand tough shipping and handling.
Onions and other Allium vegetables are herbs that are valuable to cooking but also have health-promoting properties. They can be found in many forms, from raw to cooked, grilled, powdered, and stewed.
Onions have been shown to reduce the appearance of scars, manage blood sugar, and promote cardiovascular health.
Expert Answers (Q&A)
Answered by Sarah Barreiro (Registered Dietitian)
Onions, or Allium cepa L., can be consumed raw or cooked depending on use.
The common side effects of eating raw onion are onion breath and gastric disturbance. People who are following a clinically prescribed low-FODMAP eating pattern should avoid the consumption of onion.
Yes, people with irritable bowel syndrome (IBS) or irritable bowel disease (IBD) symptoms identified by a registered dietitian or clinician or those with a diagnosed IBS/IBD following low-FODMAP eating pattern should avoid onions.
All varieties pose potential health benefits.
Possibly, according to one very small study published in the Journey of Dermatology. The study looked at a small group of individuals with an autoimmune disorder called alopecia areata. However, more research is needed to validate this claim. (23)
Onions are natural sources of the bioflavonoid called quercetin, which has a wide range of immune benefits.
One study looked at quercetin injections as a treatment for alopecia areata in mice with some improvement in the onset of spontaneous alopecia areata. (24) Again, not much research was done on this topic.
If you are struggling with hair loss, focus on your current lifestyle and basic nutritional habits first before jumping into onion juice for hair growth.
Again, quercetin seems to have potential benefit in boosting overall health and in terms of fertility, aiding in sperm mobility according to one study published in Andrology. (25)
Quercetin is a bioflavonoid found in a variety of vegetables and fruits including onions, berries, broccoli, and apples. Partners looking to conceive should consume a balanced diet rich in fruits and vegetables to be sure they are consuming variety of bioflavonoids, including quercetin.
A registered dietitian can prescribe the right amounts of bioflavonoids to consume and guide both the female and male looking to boost fertility in individualized dietary habits.
No, substantial-quality research was done on this. However, it is unlikely to cause harm if someone is desperate and wants to give it a try.
Consumption of onions is best due to the immune-enhancing micronutrients and vitamins including vitamin C. Make homemade chicken soup with bone broth vegetables and lots of onion to help provide quality nutrition when sick with the flu.
Balance and variety are the keys. You can add purple onion into a nice mixed green salad and use yellow or white onion in sauteing or cooking.
Onions provide great immune-enhancing micronutrients and vitamins and should be included for a nice source of the bioflavonoid quercetin, as well as other fruits and vegetables.
Those who have symptoms of IBS/IBD or have been following a low-FODMAP eating pattern should avoid onions. Work with a registered dietitian to identify if onions are right for you.
About Sarah Barreiro, RD: Sarah is a registered dietitian based in Houston, Texas. As a type 1 diabetic, Sarah subscribes to an all-foods-fit and integrative nutrition approach in counseling her clients.
Sarah obtained her Bachelor of Science in Dietetics and Nutrition and her MBA from Florida International University in Miami. She is also a certified personal trainer currently working with a variety of clients focusing on weight loss, hormone health, food sensitivities, and performance nutrition.