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Home > Nutrition > Onions: Nutrition, Health Benefits, and Allergy

Onions: Nutrition, Health Benefits, and Allergy

March 16, 2020 - Updated on November 2, 2022
9 min read
By Laura Krebs-Holm, MS, RD, LD | Registered Dietitian

In this article:

  • Nutritional Information
  • Types of Onions
  • Health Benefits of Onions
  • Other Possible Benefits of Onions
  • How to Buy and Store Onions
  • Safety Information
  • Most-Asked Questions About Onions
  • Expert Answers (Q&A)
  • Final Word

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.

onion benefits

An estimated 46.7 tons of onions are grown worldwide. (1) They are the third most consumed vegetable in America, falling behind potatoes, tomatoes, and corn. Most onions are consumed fresh. (2)

Nutritional Information

Onions contain vitamins A, B, and C, 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, 10% of your daily manganese needs, 5% of your daily requirement for phosphorus, and 7% of your potassium needs. (3)

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Types of Onions

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 makes them very popular in cooking.
  • Red onions: These bulbs have a red-purple skin and white flesh with a red outer layer. 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. They are not as strongly flavored nor as pungent as brown or yellow onions.
  • Green onions: These are also called spring onions, scallions, or salad onions. They have tiny white bulbs and green tops.

Health Benefits of Onions

Onions not only provide flavor and aroma to dishes but they also offer many benefits to health.

Note: While there are a few studies that support the health benefits of onion, more research is needed to warrant the dosage, safety, mechanism, and efficacy of onion in these aspects.

1. Helps to remove scars

onions can help remove scars

Applying onion extract topically may help improve the appearance, pain, and itching of different types of scars. Studies have found that onion extract may help with keloids, hypertrophic scars, and scars from tattoo removal or surgery. (4)(5)(6)

2. Helps to regulate blood sugar

Onion peel extract and quercetin have been shown to help improve glucose tolerance and overall blood sugar in rats. (7)(8) In one study, fresh raw onion improved the fasting blood glucose levels in patients with type 1 and type 2 diabetes. (9)

3. May promote cardiovascular health

Quercetin, an antioxidant found in onions, has been shown to improve blood pressure and relax blood vessels. Onion extract has been shown to lower blood pressure in patients with hypertension. (10) However, many human trials are further needed. (11)

4. Helps to manage obesity

Studies done on rats found that onion peel tea and extract were effective at reducing glucose, leptin, and cholesterol levels. (12)(13) One study found that onion peel extract may help reduce overall weight and lower body fat percentage. (14)

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5. Helps improve bone density

Onion juice may help fight against bone loss and improve bone mineral density through the antioxidant activity of various compounds present in onions. (15)(16)

Other Possible Benefits of Onions

Some studies revealed a positive correlation between onions and these health conditions:

  • Hair growth (17)
  • Cancer prevention (18)
  • Immune system boost (19)(20)
  • Antibacterial qualities (21)(22)

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.

Safety Information

While typically safe for use, those that consume large quantities of onions may experience heartburn or other gastrointestinal distress. Exposure to a cut onion may cause involuntary tearing.

Onion allergy

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.

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Drug interactions

Onions may interfere with the action of the following drugs:

  • 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.

Most-Asked Questions About Onions

general queries about onions

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.

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 help reduce crying.

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.

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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.

Expert Answers (Q&A)

Answered by Sarah Barreiro (Registered Dietitian)

Should onions be consumed in raw or cooked form?

Onions, or Allium cepa L., can be consumed raw or cooked depending on use.

What can be the side effects of eating raw onion?

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.

Which variety of onion is the most beneficial?

All varieties pose potential health benefits.

Is onion juice helpful for hair growth?

Onions may help hair growth, according to a few small studies for the improvement of alopecia areata. However, more research is needed to validate this claim. (23)(24)

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.

Does regularly consuming onions boost fertility?

Again, quercetin seems to have potential benefit in boosting overall health and, in terms of fertility, aiding in sperm mobility, according to one study. (25)

Quercetin is a bioflavonoid found in a variety of vegetables and fruits, including onions, berries, broccoli, and apples. A registered dietitian can prescribe the right amounts of bioflavonoids to consume.

Is there any proof that sleeping with an onion slice wrapped around your feet relieves flu symptoms?

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.

What points should be kept in mind when including onion in the daily diet?

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.

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’s degree 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.

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Final Word

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.

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Onions have been shown to reduce the appearance of scars, manage blood sugar, and promote cardiovascular health.

References
  1. FAO.org. Onion | Land & Water | Food andAgriculture Organization of the United Nations | Land & Water | Food and Agriculture Organization of the United Nations.http://www.fao.org/land-water/databases-and-software/crop-information/onion/en/.
  2. Food Availability and Consumption. USDA ERS – Food Availability and Consumption. https://www.ers.usda.gov/data-products/ag-and-food-statistics-charting-the-essentials/food-availability-and-consumption/.
  3. FoodData Central Search Results. FoodData Central. https://fdc.nal.usda.gov/fdc-app.html#/food-details/170000/nutrients.
  4. Draelos ZD, Baumann L, Fleischer AB, Plaum S, Avakian EV, Hardas B. A new proprietary onion extract gel improves the appearance of new scars: a randomized, controlled, blinded-investigator study. The Journal of clinical and aesthetic dermatology.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3390235/. Published June 2012.
  5. Sidgwick GP, McGeorge D, Bayat A. A comprehensive evidence-based reviewon the role of topicals and dressings in the management of skin scarring. Archives of dermatological research. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506744/. Published August 2015.
  6. Song T, Kim KH, Lee KW. Randomised comparison of silicone gel and onion extract gel for post-surgical scars. Journal of obstetrics and gynaecology: the journal of the Institute of Obstetrics and Gynaecology. https://www.ncbi.nlm.nih.gov/pubmed/29514524/. Published July 2018.
  7. Jung JY, Lim Y, Moon MS, Kim JY, Kwon O. Onion peel extracts ameliorate hyperglycemia and insulin resistance in high fat diet/streptozotocin-induced diabetic rats. Nutrition & metabolism.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074560/. Published March 28, 2011.
  8. Kook S, Kim G-H, Choi K. The antidiabetic effect of onion and garlic in experimental diabetic rats: meta-analysis. Journal of medicinal food. https://www.ncbi.nlm.nih.gov/pubmed/19627203. Published June 2009.
  9. Taj Eldin IM, Ahmed EM, Elwahab H M A. Preliminary Study of the Clinical Hypoglycemic Effects of Allium cepa (Red Onion) in Type 1 and Type 2 Diabetic Patients. Environmental health insights. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2978938/. Published October 14, 2010.
  10. Brüll V, Burak C, Stoffel-Wagner B, et al. Effects of a quercetin-rich onion skin extract on 24 h ambulatory blood pressure and endothelial function in overweight-to-obese patients with (pre-)hypertension: a randomised double- blinded placebo-controlled cross-over trial. The British journal of nutrition. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4594049/. Published October 28, 2015.
  11. Larson AJ, Symons JD, Jalili T. Quercetin: A Treatment for Hypertension?-A Review of Efficacy and Mechanisms. Pharmaceuticals (Basel, Switzerland). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3991028/. Published January 19, 2010.
  12. Matsunaga S, Azuma K, Watanabe M, et al. Onion peel tea ameliorates obesity and affects blood parameters in a mouse model of high-fat-diet-induced obesity. Experimental and therapeutic medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3881067/. Published February 2014.
  13. Yoshinari O, Shiojima Y, Igarashi K. Anti-obesity effects of onion extract in Zucker diabetic fatty rats. Nutrients. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3497009/. Published October 22, 2012.
  14. Lee J-S, Cha Y-J, Lee K-H, Yim J-E. Onion peel extract reduces the percentage of body fat in overweight and obese subjects: a 12-week, randomized, double- blind, placebo-controlled study. Nutrition research and practice. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4819128/. Published April 2016.
  15. Law Y-Y, Chiu H-F, Lee H-H, Shen Y-C, Venkatakrishnan K, Wang C-K. Consumption of onion juice modulates oxidative stress and attenuates the risk of bone disorders in middle-aged and post-menopausal healthy subjects. Food & function. https://www.ncbi.nlm.nih.gov/pubmed/26686359. Published February 2016.
  16. Matheson EM, Mainous AG, Carnemolla MA. The association between onion consumption and bone density in perimenopausal and postmenopausal non- Hispanic white women 50 years and older. Menopause (New York, N.Y.). https://www.ncbi.nlm.nih.gov/pubmed/19240657. Published 2009.
  17. Sharquie KE, Al‐Obaidi HK.Onion Juice (Alliumcepa L.), A New Topical Treatment for Alopecia Areata. Wiley Online Library. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1346-8138.2002.tb00277.x. Published July 22, 2014.
  18. Nicastro HL, Ross SA, Milner JA. Garlic and onions: their cancer prevention properties. Cancer prevention research (Philadelphia, Pa.). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4366009/. Published March 2015.
  19. Elberry AA, Mufti S, Al-Maghrabi J, et al. Immunomodulatory effect of red onion (Allium cepa Linn) scale extract on experimentally induced atypical prostatic hyperplasia in Wistar rats. Mediators of inflammation. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4009127/. Published 2014.
  20. Lee H-A, Han S-J, Hong S, Kim D-W, Oh G-W, Kim O. Onion peel water extracts enhance immune status in forced swimming rat model. Laboratory animal research. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4306703/. Published December 2014.
  21. Hannan A, Humayun T, Hussain MB, Yasir M, Sikandar S. In vitro antibacterial activity of onion (Allium cepa) against clinical isolates of Vibrio cholerae. Journal of Ayub Medical College, Abbottabad: JAMC. https://www.ncbi.nlm.nih.gov/pubmed/21702293. Published 2010.
  22. Ma Y-L, Zhu D-Y, Thakur K, et al. Antioxidant and antibacterial evaluation of polysaccharides sequentially extracted from onion (Allium cepa L.). International journal of biological macromolecules. https://www.ncbi.nlm.nih.gov/pubmed/29305215. Published May 2018.
  23. Onion Juice (Allium cepa L.), A New Topical Treatment for Alopecia Areata. ResearchGate. https://www.researchgate.net/publication/11253462/.
  24. Wikramanayake TC, Villasante AC, Mauro LM, Perez CI, Schachner LA, Jimenez JJ. Prevention and treatment of alopecia areata with quercetin in the C3H/HeJ mouse model. Cell stress & chaperones. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3273564/. Published March 2012.
  25. S; TLTPKNM. Stimulating Effects of Quercetin on Sperm Quality and Reproductive Organs in Adult Male Rats. Asian journal of andrology. https://pubmed.ncbi.nlm.nih.gov/18097532/.
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