Onion, Amazing Nutrition and Health Benefits

Onions are native to Central Asia and are now a part of cuisines around the world. They are nutritious and flavorful without a lot of calories or fat. Onion is also cholesterol-free and gluten-free , making them a healthy addition to most everyday meals.

You may have heard that onion can promote hair growth. However, research has not confirmed these common onion myths.

Onion Nutrition Facts


One medium raw onion (100 g):

  1. Calories : 40
  2. Fat 0.1 g
  3. Sodium : 4 mg
  4. Carbohydrates : 9.3 g
    1. Dietary fiber : 1.7 g
    2. Sugar : 4.3 g
  5. Protein : 1.1 g
  6. Potassium : 146 mg
  7. Vitamin C : 7.3 mg
  8. Folic acid : 19 mcg
  9. Manganese : 0.1 mg
  10. Vitamin B6 : 0.1 mg


A medium-sized 100-gram onion contains more than 10 grams of carbohydrates. Of these, 4.3 grams are sugars and 1.7 grams are dietary fiber. Onions have a low GI glycemic index rating, between 10 and 15. So onions have little effect on blood sugar.


Onions have minimal fat on their own. So when you cook onions, you usually add fat: sauté them in olive oil, canola oil, or butter , toss them in salad dressing, or bread them and deep-fry them. All of these increase the fat content of the dish.


Onions are not high in protein, with only 1.1 grams per 100 grams. If you want to increase your protein intake , use onions as a seasoning ingredient for high-protein foods (such as eggs or lean meat).

Vitamins and minerals

Onions provide a variety of nutrients , especially vitamin C, vitamin B6, folate, potassium, and manganese. When you eat onions, you’ll also take in small amounts of calcium, iron, magnesium, phosphorus, zinc, copper, selenium, choline, and other vitamins and minerals.


A 100-gram serving of a medium-sized onion provides about 40 calories. A thin slice of onion (about 9 grams) provides about 3.6 calories, while a thick slice (about 38 grams) has just over 15 calories.

Health Benefits of Onions

Onions contain a variety of natural plant compounds that can help ward off disease and promote health.

Fighting heart disease

Onions contain a compound called allyl sulfide, which helps prevent heart disease. The vitamin C in onions is also an antioxidant that benefits cardiovascular health, while its flavonoid quercetin can reduce blood pressure and inflammation.

Inhibit cancer

Allyl sulfide in onions can inhibit cancer . This includes inhibiting cancer cell development, preventing cancer cell migration, and inducing apoptosis (programmed cell death).

Reduce the risk of obesity

Most studies on the effects of onions on weight have only involved animals, but a 2021 study reported on the effects of onions on humans. The report noted that the active compounds in onions are related to weight loss .

Supports male fertility

Onion peel extract has been shown to enhance sperm motility. Research suggests the effects of onion peels may even aid in the development of infertility

Improve memory

Onions contain inulin, a soluble prebiotic fiber that provides nutrition to healthy bacteria in the gut. One study tested the effects of inulin on mood and brain performance . The study found that taking inulin was associated with improvements in short-term recall and recognition. While more research is needed, this suggests that the inulin in onions may be beneficial for cognitive function.

Onion allergies and adverse reactions

Regarding allergic symptoms to onions, such as asthma, rash, and runny nose, it is usually a case of cutting the onions rather than ingesting them. Nevertheless, allergic reactions caused by IgE-mediated reactions (as with typical food allergies) have been observed after ingestion of cooked onions .

Allergy symptoms may occur from contact with or consumption of onions, either immediately or several hours later. If you think you may be allergic to onions, consult your doctor for discussion and evaluation.

Eye irritation

Onions can irritate your eyes when you cut them. When you cut an onion, you damage its cells. The originally isolated enzyme mixes with sulfinic acid to produce propylthio S-oxide, a sulfur compound that wafts toward your eyes, causing your eyes to feel irritated. To reduce eye irritation when cutting onions, it is recommended to wear goggles before slicing onions.

Eating onions, especially raw ones, can make your breath smell very pungent. Onions contain sulfur compounds that are absorbed into the bloodstream when ingested and escape from the pores through sweat. So some people may smell like onions after eating them.

Onions also contain fructans, so people with IBS may experience abdominal pain, bloating, and gas when they eat onions.

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