Don't Miss Out

Subscribe to OCA's News & Alerts.

Can an Onion a Day Keep the Doctor Away?

A 2019 survey of 2,000 people in the U.S. crowned corn the new favorite vegetable, with an approval rating of 91%.1 Onions followed not far behind with an approval rating of 87%, making it among the top five favorite vegetables. The survey found some of the least favorite vegetables included asparagus, mushrooms and eggplant.

Many experts believe that the first onions appeared in Central Asia. Most agree the vegetable has been cultivated for nearly 5,000 years and might be one of the first cultivated crops since they are easy to grow and transport, and have a long shelf life.2

Pliny the Elder catalogued how Romans used onions in Pompeii before being killed by the volcano. His documents showed that onions’ curative powers included the ability to induce sleep, heal toothaches and mouth sores and address vision problems. Others have documented their use in the treatment of headaches and heart disease.3

In the Middle Ages, onions were used to help relieve headaches, hair loss and help to pay the rent. The first pilgrims brought them on the Mayflower to America to cultivate, where they became one of the first products brought to market in New England.

Onions are a member of the allium family, which also includes garlic, leeks, shallots and chives.4 About 125,000 acres produce 6.2 billion pounds of onions each year in the U.S.5 The top producing states are California, Eastern Oregon, Idaho and Washington.

Other countries producing a large number of onions include Turkey, Pakistan, China and India. According to Live Science, the average person in the U.S. eats 20 pounds of onions each year.

Nutrient Value Basis of Onion’s Health Benefits

It's likely the many health benefits derived from eating onions comes from the nutrient value of the vegetable. One small onion has just 28 calories, 6.5 grams (g) of carbohydrate and 1.1 g of total fiber. It also contains:6

  • Calcium, 16.1 milligrams (mg)
  • Magnesium, 7 mg
  • Potassium, 102 mg
  • Vitamin C, 5.18 mg
  • Choline, 4.27 mg


Onions are also surprisingly high in beneficial polyphenols.7 This group of plant compounds plays an important role in the prevention and reduction of diabetes, cancer and cardiovascular diseases. In a comparison of the polyphenol and antioxidant capacity between red and yellow onions researchers found the outer layers of the onions had the highest number of total polyphenols and flavonoids.

The outer layers of both types of onions also had the highest antioxidant activity. However, overall, the red onion had better antioxidant activity, with a higher number of total polyphenols and flavonoids that were associated with antioxidant activity. Onions have over 25 varieties of flavonoids that help prevent cellular damage contributing to chronic diseases such as diabetes and heart disease.

In addition to the calcium content promoting strong bones, onions may also relieve oxidative stress, which in turn decreases bone loss and can help prevent osteoporosis.8 Onions are also good sources of vitamins A and K, which in addition to vitamin C help protect your skin from ultraviolet rays. Vitamin C also helps your body produce collagen, a structural support for your skin and hair.

Prebiotic Compound Has Multiple Benefits

Prebiotics are indigestible fiber that help nourish the beneficial bacteria in your body. In turn, these bacteria help with digestion and absorption of your food, as well as play a significant role in the function of your immune system. One of these prebiotics is inulin, a water-soluble form of dietary fiber that's found in onions.9

Inulin is found in thousands of species of plants, but most experts agree that chicory root is the richest source with up to 20 g of inulin per 100 g in weight. Jerusalem artichokes, garlic, asparagus and raw onion are also significant sources, with Jerusalem artichokes measuring up to 19 g and raw onion measuring from 5 to 9 g.10

Your gut thrives on adequate amounts of fiber as it helps improve digestive health and relieves constipation. In one study, researchers found those who took inulin had bowel movements with improved stool consistency,11 and another four-week study showed older adults experienced better digestion with less constipation.12

In addition to feeding the beneficial bacteria in your gut microbiome, inulin also demonstrates the ability to promote weight loss and reduce liver fat cells in people who are prediabetic.13

Since inulin is colorless, has a neutral taste and is highly soluble, manufacturers are adding it to food products to help increase the fiber content of processed foods.14 In a review of inulin studies published in U.S. Pharmacist, the data showed inulin also has an effect on mineral absorption and a potential effect on lipid levels.15

Several studies showed it helps improve calcium absorption, which is highly beneficial in the onion since it is also a rich source of calcium. Overall, the data on the effect on lipids were mixed as most studies had a small number of participants. However, past research has shown that soluble fiber does lower lipid levels.16

In one study of women who had Type 2 diabetes, the researchers found those with inulin supplementation had better glycemic control.17 It also appears that flavonoid-rich foods such as onions may help inhibit the growth of H. pylori, a type of bacteria responsible for most ulcers.18

Order Ronnie's New Book: Grassroots Rising

Get Local

Find News and Action for your state:
$5 Off Your Next Order at and 20% Goes to Organic Consumers Association.