What is an Onion?
The onion, also known as the bulb onion or common onion, that grows underground is a vegetable that is the most widely cultivated species of the genus Allium. The shallot is a botanical variety of the onion. Until 2010, the shallot was classified as a separate species.
Onions belong to the Allium family of plants, which also includes chives, garlic, and leeks. These vegetables have characteristic pungent flavors and some medicinal properties.
Onions vary in size, shape, color, and flavor. The most common types are red, yellow, and white onions. The taste ranges from mild and sweet to sharp and spicy, depending on the variety and season.
Commonly used as a flavoring or side dish, onions are a staple food in many cuisines. They can be baked, boiled, grilled, fried, roasted, sautéed, powdered, or eaten raw.
Onions can also be consumed when immature before the bulb reaches full size. They are then called scallions, spring onions, or summer onions.
Raw onions are very low in calories, with only 40 calories per 3.5 ounces (100 grams).
By fresh weight, they are 89% water, 9% carbs, and 1.7% fiber, with tiny amounts of protein and fat.
The main nutrients in 3.5 ounces (100 grams) of raw onions are:
- Calories: 40
- Water: 89%
- Protein: 1.1 grams
- Carbs: 9.3 grams
- Sugar: 4.2 grams
- Fiber: 1.7 grams
- Fat: 0.1 grams
Carbohydrates make up about 9–10% of both raw and cooked onions.
They consist mostly of simple sugars, such as glucose, fructose, and sucrose, as well as fiber.
A 3.5-ounce (100-gram) portion contains 9.3 grams of carbs and 1.7 grams of fiber, so the total digestible carb content is 7.6 grams.
Onions are a decent source of fiber, which accounts for 0.9–2.6% of the fresh weight, depending on the type of onion.
They are very rich in healthy soluble fibers called fructans. In fact, onions are among the main dietary sources of fructans.
Fructans are so-called prebiotic fibers, which feed the beneficial bacteria in your gut.
This leads to the formation of short-chain fatty acids (SCFAs), such as butyrate, which may improve colon health, reduce inflammation, and cut your risk of colon cancer.
Vitamins and minerals
Onions contain decent amounts of several vitamins and minerals, including:
- Vitamin C. (RDA) An antioxidant, this vitamin is needed for immune function and maintenance of skin and hair 13.11% for males and 15.73% for females ( Percentage of the daily requirement in adults).
- Folate (B9). A water-soluble B vitamin, folate is essential for cell growth and metabolism and especially important for pregnant women.
- Vitamin B6. (RDA) 11.29–14.77%, depending on age. (Percentage of the daily requirement in adults) Found in most foods, this vitamin is involved in the formation of red blood cells.
- Potassium. This essential mineral can have blood-pressure-lowering effects and is important for heart health.
- Manganese (Al) 8.96% for males and 11.44% for females (Percentage of the daily requirement in adults)
One cup of chopped onion provides:
- 64 calories
- 14.9 grams (g) of carbohydrate
- 0.16 g of fat
- 0 g of cholesterol
- 2.72 g of fiber
- 6.78 g of sugar
- 1.76 g of protein
Other plant compounds
The health benefits of onions are attributed to their antioxidants and sulfur-containing compounds.
In many countries, onions are also among the main dietary sources of flavonoids, specifically, a compound called quercetin.
The most abundant plant compounds in onions are:
- Anthocyanins. Only found in red or purple onions, anthocyanins are powerful antioxidants and pigments that give these onions their reddish color.
- Quercetin. An antioxidant flavonoid, quercetin may lower blood pressure and improve heart health.
- Sulfur compounds. These are mainly sulfides and polysulfides, which may protect against cancer.
- Thiosulfinates. These sulfur-containing compounds may inhibit the growth of harmful microorganisms and prevent the formation of blood clots.
Cooking can significantly reduce levels of some antioxidants/
6 Types of Onions and How to Use Them
1. Yellow Onions
Good for: All recipes—especially caramelizing
If a recipe doesn’t specify what type of onion to use, your safest bet is a yellow onion. “Yellow onions are your standard cooking onion. I always reach for a yellow onion unless I have some other reason to reach for something else,” says Kim Reddin, the director of public and industry relations for the National Onion Association.
“The yellows hold up extremely well over that process of caramelizing because it is a long, slow heat.”
2. Sweet Onions
Good for: Salads, relishes, garnishes
Popular sweet onions include Vidalias, Walla Wallas and Mauis. “These well-known varieties have pale yellow skin. The inside may look white but they are yellow,” says Reddin, who fields questions about onions as The Onionista.
If you’re looking for an onion that tastes amazing raw in salads, relishes, or chopped as a garnish, go for sweet onions. “They just have that mild onion flavor with a touch of sweetness that you can use in a number of things.”
3. Red Onions
Good for: Salads, grilling, and pickling
Red onions are ubiquitous on salads, sandwiches, and other raw preparations partly because of their appealing deep-purple color. Reddin warns, however, “Red onions, specifically, can have a really peppery, spicy flavor to them.”
This variety is sweetest from March to September. Red onions pair well with equally strong-flavored greens such as kale or arugula. Reddin also recommends red onions for roasting, grilling, and pickling.
4. White Onions
Good for: Mexican dishes and grilling
White onions it the type of onion you’ll usually find in prepared salads (potato and macaroni salads, for instance) and traditionally in Mexican cuisine. “White onions can be strong but they tend to have less aftertaste,” Reddin says.
Good for: Sauces and dressings
Shallots have a mild onion flavor. These bulb-shaped alliums taste like a garlic-onion hybrid. In French cooking, shallots are used in vinaigrette and sauces, as well as on top of, steak.
When a recipe calls for a shallot and you don’t have one, you can likely substitute another type of onion for it.
Good for: Asian and Mexican cooking and garnishes
These two-tone onions can be eaten cooked or raw. Scallions are popular in Chinese and Mexican cuisine. In Chinese cooking, scallions are used in stir-fries, soups, stews, and braised dishes.
Scallions or green onions have a milder flavor than regular onions.
9 Health Benefits of Onions
Onions may have several health benefits, mostly due to their high content of antioxidants and sulfur-containing compounds.
They have antioxidant and anti-inflammatory effects and have been linked to a reduced risk of cancer, lower blood sugar levels, and improved bone health.
1. Packed With Antioxidants
Antioxidants are compounds that inhibit oxidation, a process that leads to cellular damage and contributes to diseases like cancer, diabetes, and heart disease.
Onions are an excellent source of antioxidants. In fact, they contain over 25 different varieties of flavonoid antioxidants.
Red onions, in particular, contain anthocyanins — special 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 men showed that habitual intakes as high as 613 mg per day of anthocyanins were correlated to a 14% lower risk of nonfatal heart attacks.
Similarly, a study in 93,600 women observed that those with the highest intake of anthocyanin-rich foods were 32% less likely to experience a heart attack than women with the lowest intake.
2. Have Antibacterial Properties
Furthermore, onion extract has been shown to inhibit the growth of Vibrio cholerae, a bacterium that is a major public health concern in the developing world.
Quercetin extracted from onions seems to be a particularly powerful way to fight bacteria.
A test-tube study demonstrated that quercetin extracted from yellow onion skin successfully inhibited the growth of Helicobacter pylori (H. Pylori) and Methicillin-resistant Staphylococcus aureus (MRSA).
Another test-tube study found that quercetin damaged the cell walls and membranes of E. coli and S. Aureus.
3. Loaded With Nutrients
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.
This vegetable is particularly high in vitamin C, a nutrient involved in regulating immune health, collagen production, tissue repair, and iron absorption.
Vitamin C also acts as a powerful antioxidant in your body, protecting your cells against damage caused by unstable molecules called free radicals.
Onions are also rich in B vitamins, including folate (B9) and pyridoxine (B6) — which play key roles in metabolism, red blood cell production, and nerve function
Lastly, they’re a good source of potassium, a mineral in which many people are lacking. In fact, the average potassium intake of Americans is just over half the recommended daily value (DV) of 4,700 mg.
Normal cellular function, fluid balance, nerve transmission, kidney function, and muscle contraction all require potassium.
4. Help Control Blood Sugar
Eating onions may help control blood sugar, which is especially significant for people with diabetes or prediabetes.
A study in 42 people with type 2 diabetes demonstrated that eating 3.5 ounces (100 grams) of fresh red onion reduced fasting blood sugar levels by about 40 mg/dl after four hours.
Additionally, multiple animal studies have shown that onion consumption may benefit blood sugar control.
A study showed that diabetic rats fed food containing 5% onion extract for 28 days experienced decreased fasting blood sugar and had substantially lower body fat than the control group.
Specific compounds found in onions, such as quercetin and sulfur compounds, 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.
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 women showed that those who consumed 3.4 ounces (100 ml) of onion juice daily for eight weeks had improved bone mineral density and antioxidant activity compared to a control group.
Another study in 507 perimenopausal and postmenopausal women 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.
Plus, the study demonstrated that older women who most frequently ate onions decreased their risk of hip fracture by more than 20% compared to those who never ate them.
It’s believed that onions help reduce oxidative stress, boost antioxidant levels and decrease bone loss, which may prevent osteoporosis and boost bone density.
6. Contain Cancer-Fighting Compounds
Eating vegetables of the Allium genus like garlic and onions has been linked to a lower risk of certain cancers, including stomach and colorectal.
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 least amount.
Moreover, a review of 16 studies in 13,333 people demonstrated that participants with the highest onion intake had a 15% reduced risk of colorectal cancer compared to those with the lowest intake
These cancer-fighting properties have been linked to the sulfur compounds and flavonoid antioxidants found in allium vegetables.
7. May Boost Digestive Health
Onions are a rich source of fiber and prebiotics, which are necessary for optimal gut health.
Prebiotics are non-digestible 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.
Research has shown that these short-chain fatty acids strengthen gut health, boost immunity, reduce inflammation and enhance digestion.
A diet rich in prebiotics may help improve the absorption of important minerals like calcium, which may improve bone health.
Onions are particularly rich in prebiotic inulin and fructooligosaccharides. These help increase the number of friendly bacteria in your gut and improve immune function.
8. May Benefit Heart Health
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.
A study in 70 overweight people with high blood pressure found that a dose of 162 mg per day of quercetin-rich onion extracts significantly reduced systolic blood pressure by 3–6 mm Hg compared to a placebo.
Onions have also been shown to decrease cholesterol levels.
A study in 54 women with, polycystic ovarian syndrome (PCOS) found that consuming large amounts of raw red onions (40–50 grams/day if overweight and 50–60 grams/day if obese) for eight weeks reduced total and “bad” LDL cholesterol compared to a control group (Trusted Source).
9. Easy to Add to Your Diet
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.
- 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 sauteed 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.
Please let us know in the comments below:
- Have you been eating onions? Raw or Cooked?
- Do you have a certain illness that the onion helps alleviate? If so, which kind do you use?
- Do you have any more onion recipes you can share with us aside from the above lists?
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Information on this site is not intended to diagnose, treat, cure, or prevent any disease. We encourage you to do your own research. Seek the advice of a medical professional before making any changes to your lifestyle or diet.
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