Benefits Of Onion For Weight Loss

What is an onion?

Onion is the most commonly cultivated vegetable after tomatoes. They belong to the genus Allium in the Alliaceae family. The red colour of onions is due to the composition called anthocyanins present in outer layers of leaves of the bulb.¹

Onions  are a multi-use vegetable, most commonly used as flavouring agent or in a salad. It is a staple food in many cuisines. They can be baked, boiled, grilled, fired, roasted, sauteed, powdered and also can be eaten raw.¹

Onions are a rich source of flavanols which are not affected by roasting, frying or cooking. Onion leaves have been used as herbal medicine for cold, influenza, abdominal pain, headache, constipation and diarrhoea.²

Onions have been used as medicine by the Chinese; to warm the lungs and reduce phlegm; warm the stomach during digestion; detoxify and destroy intestinal worms; and decreasing soreness and swelling.³

Onions are also a rich source of quercetin, a flavonoid most commonly seen in onions, apple and green tea, proven to have many health benefits. Onions are a rich source of quercetin -140 g contains 109 mg of quercetin aglycone.⁴

In many studies, it is proven that quercetin hasantioxidant and antihypertensive properties  which can also help in weight loss.⁴

Does onion help you lose weight?

Benefits of onion for weight loss

Onions are a rich source of fibre, which makes your stomach full and reduces the intake of food.

The flavonoid quercetin present in the onion has antioxidant, anti inflammatory and lipid regulating properties, proven to aid in weight loss. 

Quercetin helps to: 

  • Regulate lipid metabolism
  • Regulate carbohydrate metabolism
  • Increase glucose absorption
  • Increase insulin sensitivity
  • Increase insulin response by the cells
  • Reduces the formation of fat cells
  • Regulate the percentage of fat in the body
  • Prevent fat deposition in the liver
  • Reduce the fat in hands and stomach
  • Reduce body metabolic index (BMI)⁵,

Many studies conducted in miceshowed that consumption of quercetin reduced fat quantity, reduced their BMI and helped in weight reduction compared to the control groups.

Other health benefits of onion

In addition to lipid regulation, onions are proven to have: 

  • Antioxidative property- that reduced free moving radicals 
  • Antihypertensive properties- reduced blood pressure
  • Anticoagulative properties- prevents formation of blood clots
  • Antiinflammatory factors- reduces inflammation
  • Antifungal properties
  • Protects health of nerves- neuroprotective
  • Increases immunity-immunoprotective
  • Reduce fasting blood sugar levels- glucose metabolism
  • Helps in prevention of cancer
  • Coordination in heavy metal detoxification
  • Help in expulsion of other toxins
  • Prevents kidney damage due to diabetes- diabetic nephropathy
  • Reduce blood pressure
  • Prevents heart attacks- cardiovascular disorders
  • Treatment of asthma
  • Treatment of anxiety, depression⁵,

Through the process of fat regulation and reducing blood pressure, onions can reduce the damage to arteries. Thus, they can also help in preventing heart attacks.As their calorie count is very little compared to other vegetables, the intake of onions won't affect anyone's diet.

All these properties are attributed to the presence of higher concentrations of flavonoids and prebiotics in the onions..⁷

A study conducted in animals who were fed with onions on a regular basis showed that their triglycerides have shown adequate reduction with increased insulin sensitivity and response. The author concluded that obesity can cause liver deformation by excess fat deposition and functional issues. These issues can also be prevented by regular use of onions.⁷

Nutritional facts

The nutritional value of onion is found to have low fat, vitamins (vitamin B6) and iron.² 

100 g of onions contains 40 calories of energy with the following constituents:

  1. Fats- 0.1g
  2. Potassium-146 mg
  3. Sodium - 4mg
  4. Carbohydrate-9 g
  5. Dietary fibre-1.7g
  6. Sugar- 4.2g
  7. Protein-1.1g
  8. Vitamin C- 12%
  9. Iron- 1%
  10. Vitamin B6- 5%
  11. Magnesium -2%
  12. Calcium- 2%

Side effects and other concerns

Onions give a scented breath in the mouth when consumed in its raw form. This property is due to the presence of  sulphur compounds.Onions consumed may result in aggravating heartburn in those who have hada previous history.⁸

Irrespective of these, there were no other side effects reported following the consumption of onions.²


Onion cultivation dates backto BC times in different countries of the world. There are different species, but all can contribute to many health benefits when consumed. With minimal or no side effects, this has made it the most common vegetable consumed in raw or cooked form for all.  As the calories in onion are minimal, it sure helps in maintaining your diet goals.  Along with its property of lipid maintenance, carbohydrate and insulin regulation, onions can play a crucial role  in maintaining the good health and weight of an individual.


  1. Sidhu JS, Ali M, Al-Rashdan A, Ahmed N. Onion (Allium cepa L.) is potentially a good source of important antioxidants. J Food Sci Technol 2019;56:1811–9.
  2. Sung Y-Y, Kim D-S, Kim S-H, Kim HK. Aqueous and ethanolic extracts of welsh onion, Allium fistulosum, attenuate high-fat diet-induced obesity. BMC Complement Altern Med 2018;18:105.
  3. Yang C, Li L, Yang L, Lǚ H, Wang S, Sun G. Anti-obesity and Hypolipidemic effects of garlic oil and onion oil in rats fed a high-fat diet. Nutr Metab (Lond) 2018;15:43.
  1. Nishimura M, Muro T, Kobori M, Nishihira J. Effect of Daily Ingestion of Quercetin-Rich Onion Powder for 12 Weeks on Visceral Fat: A Randomised, Double-Blind, Placebo-Controlled, Parallel-Group Study. Nutrients 2019;12:91.
  2. 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. Nutr Res Pract 2016;10:175–81.
  3. Galavi A, Hosseinzadeh H, Razavi BM. The effects of Allium cepa L. (onion) and its active constituents on metabolic syndrome: A review. Iran J Basic Med Sci 2021;24:3–16.
  4. Emamat H, Foroughi F, Eini-Zinab H, Hekmatdoost A. The Effects of Onion Consumption on Prevention of Nonalcoholic Fatty Liver Disease. Indian J Clin Biochem 2018;33:75–80.
  5. Allen ML, Mellow MH, Robinson MG, Orr WC. The effect of raw onions on acid reflux and reflux symptoms. Am J Gastroenterol 1990;85:377–80.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Swathi Gadadasu

I am Dr Swathi G, from India, with experience as a dental clinician for 8 years, oral physician and Oral Maxillofacial Radiologist for 4 years, an academician for 3.5 years, an academic writer for 3 years and a medical writer for 1 year. With sound knowledge of clinical, non-clinical, scientific and academic and medical writing, working as a Freelancer Writer at Work foster. Due to my passion for writing, completed many national and international Publications in various indexed and well-known journals.

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