Onions are highly nutritious and have been associated with several benefits, including improved heart health, better blood sugar control, and increased bone density.
Though all vegetables are important for health, certain varieties offer unique benefits.
Onions are members of the Allium genus of flowering plants that also includes garlic, shallots, leeks, and chives.
These vegetables contain various vitamins, minerals, and potent plant compounds that have been shown to promote health in many ways.
Here are 9 impressive health benefits of onions.
Onions are nutrient-dense, meaning they’re low in calories but high in vitamins and minerals.
One medium onion has just 44 calories but delivers a considerable dose of vitamins, minerals, and fiber (2Trusted Source).
This vegetable is particularly high in vitamin C, a nutrient involved in regulating immune health, collagen production, tissue repair, and iron absorption.
Lastly, they’re a good source of potassium, a mineral which many people are lacking.
In fact, the average potassium intake of Americans is less than half the recommended daily value (DV) of 4,700 milligrams (mg) (5Trusted Source).
Normal cellular function, fluid balance, nerve transmission, kidney function, and muscle contraction all require potassium (6Trusted Source).
Onions contain antioxidants and compounds that fight inflammation, decrease triglycerides, and reduce cholesterol levels — all of which may lower heart disease risk.
Their potent anti-inflammatory properties may also help reduce high blood pressure and protect against blood clots.
Quercetin is a flavonoid antioxidant that’s highly concentrated in onions. Since it’s a potent anti-inflammatory, it may help decrease heart disease risk factors, such as high blood pressure (7Trusted Source).
A study in 70 people with overweight and high blood pressure found that a dose of 162 mg per day of quercetin-rich onion extract significantly reduced systolic blood pressure by 3–6 millimeters of mercury (mmHg), compared to a placebo (8Trusted Source).
Onions have also been shown to decrease cholesterol levels.
A 2014 study in 54 females with polycystic ovarian syndrome (PCOS) found that consuming large amounts of raw red onions (80–120 grams per day) for 8 weeks reduced total and LDL (bad) cholesterol compared to a control group (9Trusted Source).
Additionally, evidence from animal studies supports that onion consumption may reduce risk factors for heart disease, including inflammation, high triglyceride levels, and blood clot formation (10Trusted Source, 11Trusted Source, 12Trusted Source).
Red onions, in particular, contain anthocyanins, which are plant pigments in the flavonoid family that give red onions their deep color.
Multiple population studies have found that people who consume more foods rich in anthocyanins have a reduced risk of heart disease.
For example, a study in 43,880 males showed that habitual intakes as high as 613 mg per day of anthocyanins were correlated to a 14% lower risk of nonfatal heart attacks (15Trusted Source).
Eating vegetables of the Allium genus like garlic and onions has been linked to a lower risk of certain types of cancer, including stomach and colorectal cancer.
A review of 26 studies showed that people who consumed the highest amount of allium vegetables were 22% less likely to be diagnosed with stomach cancer than those who consumed the lowest amount (19Trusted Source).
Moreover, a 2014 review of 16 studies in 13,333 people demonstrated that those with the highest onion intake had a 15% reduced risk of colorectal cancer compared to those with the lowest intake (20Trusted Source).
These cancer-fighting properties have been linked to the sulfur compounds and flavonoid antioxidants found in allium vegetables.
For example, onions provide onionin A, a sulfur-containing compound that has been shown to decrease tumor development and slow the spread of ovarian and lung cancer in test-tube studies (21Trusted Source, 22Trusted Source).
Eating onions may help control blood sugar, which is especially significant for people with diabetes or prediabetes.
An older study in 42 people with type 2 diabetes demonstrated that eating 3.5 ounces (oz), or 100 grams, of raw red onion significantly reduced fasting blood sugar levels after 4 hours (25Trusted Source).
Additionally, multiple animal studies have shown that onion consumption may benefit blood sugar control.
A study showed that rats with diabetes fed food containing 5% dried onion powder for 8 weeks experienced decreased fasting blood sugar levels and had lower triglyceride and cholesterol levels compared to a control group (26Trusted Source).
Specific compounds found in onions, such as quercetin and sulfur compounds, also possess antidiabetic effects.
For example, quercetin has been shown to interact with cells in the small intestine, pancreas, skeletal muscle, fat tissue, and liver to control whole-body blood sugar regulation (27Trusted Source).
Though dairy gets much of the credit for boosting bone health, many other foods, including onions, may help support strong bones.
A study in 24 middle-aged and postmenopausal females showed that those who consumed 3.4 oz (100 milliliters) of onion juice daily for 8 weeks had improved bone mineral density and antioxidant activity compared to a control group (28Trusted Source).
Another older study in 507 perimenopausal and postmenopausal females found that those who ate onions at least once a day had a 5% greater overall bone density than individuals who ate them once a month or less (29Trusted Source).
Plus, the study demonstrated that older individuals who most frequently ate onions decreased their risk of hip fracture by more than 20% compared to those who never ate them (29Trusted Source).
Onions can fight potentially dangerous bacteria, such as Escherichia coli (E. coli), Pseudomonas aeruginosa, Staphylococcus aureus (S. aureus), and Bacillus cereus (31Trusted Source).
Furthermore, onion extract has been shown to inhibit the growth of Vibrio cholerae, a bacteria that is a major public health concern in some parts of the world (32Trusted Source).
Quercetin extracted from onions seems to be a particularly powerful way to reduce the growth of bacteria.
Some test-tube studies suggest that quercetin could inhibit the growth of several strains of bacteria, including Helicobacter pylori (H. pylori), a type of bacteria associated with stomach ulcers and certain digestive cancers (33Trusted Source, 34Trusted Source).
Another test-tube study found that quercetin damaged the cell walls and membranes of E. coli and S. aureus (35Trusted Source).
Onions are a rich source of fiber and prebiotics, which are necessary for optimal gut health.
Prebiotics are nondigestible types of fiber that are broken down by beneficial gut bacteria.
Gut bacteria feed on prebiotics and create short-chain fatty acids — including acetate, propionate, and butyrate.
Onions are a staple in kitchens around the world.
They give flavor to savory dishes and can be enjoyed either raw or cooked.
Not to mention, they can boost your intake of fiber, vitamins, and minerals.
Here are some tips on how to add onions to your diet:
- Use raw onions to add a kick of flavor to your guacamole recipe.
- Add caramelized onions to savory baked goods.
- Combine cooked onions with other vegetables for a healthy side dish.
- Try adding cooked onions to egg dishes, such as omelets, frittatas, or quiches.
- Top meat, chicken, or tofu with sautéed onions.
- Add thinly sliced red onions to your favorite salad.
- Make a fiber-rich salad with chickpeas, chopped onions, and red peppers.
- Use onion and garlic as a base for stocks and soups.
- Throw onions into stir-fry dishes.
- Top tacos, fajitas, and other Mexican dishes with chopped raw onions.
- Make a homemade salsa with onions, tomatoes, and fresh cilantro.
- Prepare a hearty onion and vegetable soup.
- Add onions to chili recipes for a flavor boost.
- Blend raw onions with fresh herbs, vinegar, and olive oil for a tasty homemade salad dressing.
The health benefits related to onions are quite impressive.
These nutrient-packed vegetables contain powerful compounds that may decrease your risk of heart disease and certain cancers.
Onions have antibacterial properties and promote digestive health, which may improve immune function.
What’s more, they’re versatile and can be used to heighten the flavor of any savory dish.
Adding more onions to your diet is an easy way to benefit your overall health.