Nutrition Facts & Overview of Onion Calories

    An Overview of Onion Calories

    Martin Alvarez

    Martin Alvarez
    Nutritionist/Dietitian Professional Guide

    Updated on 11/26/2022

    The onion (Allium cepa) is a bulb-shaped vegetable that grows underground.

    Also known as bulb onions or common onions, they are grown in many parts of the world and are closely related to other onions such as chives, garlic, scallions, shallots, and leeks.

    One of the primary reasons why onions are beneficial to one's health is likely because they contain high levels of antioxidants, onion calories, and sulfur-containing compounds that are found in them.

    One of the most fundamental ingredients in a wide range of cuisines, onions are most frequently used in seasoning or as a side dish with various other ingredients. It is possible to cook them in multiple ways, including baking, boiling, grilling, frying, roasting, sautéing, powdering, or eating them raw, depending on the type of preparation.

    White, yellow, and red onions are the most common, but You can also find onions in various shapes, sizes, and colors. Its taste can range from mild and sweet to sharp and spicy, depending on the variety and season.

    In addition, onions may also be consumed when they are still immature before the bulb has reached its full size when they are still green. As a result, people refer to these onions as scallions, spring onions, or summer onions.

    As a result of this article, you will be able to find all the information about the onions you need.

    Onion Facts About Nutrition

    raw onions is meager


    The amount of calories in raw onions is meager, as they only contain 40 calories per 3.5 ounces (100 grams).

    In terms of their fresh weight, they are composed of 89 percent water, 9 percent carbohydrates, and 1.7 percent fiber, with traces of proteins and fat, which are present in small amounts.

    Raw Onions Contain The Following Nutrients in 3.5 Ounces (100 grams):

    • Calories: 40
    • Water: 89%
    • Protein: 1.1 grams
    • Carbs: 9.3 grams
    • Sugar: 4.2 grams
    • Fiber: 1.7 grams
      • Fat: 0.1 grams




    Approximately 9–10% of the weight of both uncooked and cooked onions is made up of carbohydrates.

    As a result, they are mainly composed of essential sugars such as glucose, fructose, and sucrose, in addition to dietary fiber.

    A serving of 3.5 ounces (100 grams) contains 1.7 grams of fiber and 9.3 grams of carbohydrates, so the total amount of carbs the body can digest is 7.6 grams per serving.




    Onions contain between 0.9 and 2.6% of their fresh weight as fiber, depending on the onion's variety and size. In this way, onions are considered a good fiber source.

    A large number of fructans can be found in them, which are a type of beneficial soluble fiber that has many health benefits. Onions represent one of the essential sources of fructans from foods humans consume.

    In essence, fructans are known as "prebiotic fibers" because they provide food for the good bacteria that are already present in your digestive tract, allowing them to flourish.

    As a result, short-chain fatty acids (SCFAs) are produced during this process, including butyrate, which has been shown to improve colon health, lower inflammation levels, and lower the risk of colon cancer over time.

    In contrast, fructans are a type of FODMAP, compounds that have been shown to aggravate the digestive systems of people who are sensitive to them, such as those who suffer from irritable bowel syndrome (IBS).


    Onions have three main components: water, carbohydrates, and fiber. While they may cause digestive issues for some people, their primary fibers, known as fructans, can provide food for the beneficial bacteria in your digestive tract, even though they may cause digestive problems.

    Vitamins & Minerals, Respectively

    Vitamins & Minerals Included in Onions Include:

    Vitamins & Minerals, Respectively


    • In addition to being an antioxidant, vitamin C is also essential for maintaining skin and hair health and ensuring proper immune system function.
    • There is a vitamin called folate (B9) (B9). In particular, pregnant women are especially in need of folate, a water-soluble B vitamin that is necessary for the growth and metabolism of their cells.
    • B6 is a vitamin that plays a vital role in the body. The vitamin is found in almost every type of food and plays a crucial role in the body's production of red blood cells.
    • The mineral potassium. It has been demonstrated that this mineral plays a vital role in maintaining a healthy heart function and that it can reduce blood pressure to a great extent.


    It is important to note that onions contain moderate amounts of beneficial nutrients such as vitamin C, folate, vitamin B6, and potassium. These nutrients contribute to the onion's long list of health benefits.

    Other Chemical Components of Plants

    Other Chemical Components of Plants


    The antioxidants, as well as the compounds that contain sulfur found in onions, are thought to be responsible for their health-promoting properties, as they are supposed to have anti-inflammatory properties.

    Worldwide, onions are considered to be one of the most important dietary sources of flavonoids, specifically a substance called quercetin, in a wide range of countries.

    Onions Contain the Highest Concentrations of These Plant Compounds:

    • Anthocyanins are antioxidants. In red or purple onions, anthocyanins are potent antioxidants, and pigments are only found in red or purple plants. The stains in these onions are responsible for the reddish color of these onions.
    • The antioxidant quercetin. It is a type of flavonoid that acts as an antioxidant and may help lower blood pressure and improve the heart's health.
    • The compounds that contain sulfur are known as sulfur compounds. In most cases, these substances are sulfides and polysulfides, which protect against cancer.
    • The thiosulfinates. The sulfur-containing compounds in these compounds may prevent the formation of blood clots and the growth of potentially harmful microorganisms.

    The antioxidant content of red and yellow onions is significantly higher than that of other types of onions. Even though there is evidence to suggest that yellow onions contain almost 11 times the amount of antioxidants that white onions do, there is still some research to support that conclusion.

    The cooking process can significantly diminish the levels of some antioxidants.


    One of the plant compounds and antioxidants abundant in onions is quercetin, one of the sulfur-containing compounds in onions. Compared to their colorful counterparts, such as yellow or red varieties, white varieties contain fewer antioxidants than their colorful counterparts.

    Onions Positive Effects on One's Health

    Onions Positive Effects on One's health


    Onions are known to possess potent anti-inflammatory and antioxidant properties, as proven in studies.

    Blood Sugar Regulation

    Blood Sugar Regulation


    As the most prevalent form of diabetes, type 2 diabetes is characterized by a high blood sugar level, which is a primary indicator of the illness.

    Research conducted on animals hints that onions may be able to bring blood sugar levels down.

    The same findings have been demonstrated in human subjects as well. The study found that people with type 2 diabetes who consumed raw onions at a rate of 3.5 ounces (100 grams) daily experienced a significant drop in their blood sugar levels at the end of the study.

    In theory, it might be possible that eating raw onions can help reduce the risk of diabetes type 1 and type 2, but further study has to be done to test this hypothesis.

    The Health of The Bones

    The health of The Bones


    In recent years, osteoporosis has become a prevalent health issue, particularly among women who have gone through menopause. You must maintain a healthy diet as one of the most important preventative measures you can take.

    Onions have been shown to prevent the breakdown of bone tissue and may even increase bone density based on animal research.

    In a large observational study involving a large number of women over 50, They found that your regular consumption of onions is associated with increased bone density.

    Research suggests that postmenopausal women who consume particular fruits, vegetables, herbs, and spices, such as onions, may experience less bone loss.

    Reduced Likelihood of Developing Cancer



    Cancer development is a widespread disease characterized by the uncontrolled growth of cells over a long period. All over the world, it is one of the most significant contributors to the increase in mortality rates.
    The results of studies that take a more observational approach, for example, have shown that eating more onions correlates with having a lower risk of several types of cancer, such as those of the stomach, breast, colon, and prostate.


    In addition to having antioxidant properties, onions also have anti-inflammatory properties. Furthermore, they may lower the risk of some types of cancer, improve bone health, and lower blood sugar levels.

    Potential Downsides

    Potential Downsides


    Two potential side effects of eating onions are onion breath and a smelly body odor.

    Due to various other drawbacks associated with this vegetable, some individuals may not be able to consume this vegetable.

    Intolerance to Onions & Onion Allergy

    Intolerance to Onions & Onion Allergy


    It should be noted that onion allergies are rare, but onion intolerances, particularly those caused by raw onion varieties, are pretty standard.

    As a result of onion intolerance, one may experience digestive symptoms such as bloating, heartburn, and gas, as well as other digestive issues.

    Some people can have allergic reactions just by touching onions, regardless of whether or not they have a food allergy to onions, irrespective of whether or not they have a food allergy.




    It is important to remember that FODMAPs, also known as fructans, oligosaccharides, polyols, and polyols, are a group of carbohydrates and fibers that many people have difficulties digesting.

    In addition to bloating, gas, cramping, and diarrhea, they can cause various unpleasant digestive symptoms.

    Onions should probably be avoided by those who suffer from irritable bowel syndrome since they are frequently intolerant to FODMAPs.

    Irritation to The Mouth & The Eyes

    Irritation to The Mouth & The Eyes


    As a result of the preparation and cutting of onions, one of the most common problems that arise is eye irritation and excessive tear production. The cells within an onion generate a gas known as a lachrymatory factor (LF) when they are cut, which is then released by the cells.

    The gas stimulates neurons in your eyes, causing a burning sensation followed by tears to wash away the irritant.

    While cutting an onion, it is a good idea to leave the root end whole to reduce irritation because the base of the onion contains a higher concentration of the substances that irritate the bulb.

    To prevent the release of this gas into the atmosphere, chopping onions under running water may also be a good idea.

    Furthermore, it is thought that LF is responsible for the burning sensation in the mouth when raw onions are consumed. There is a possibility that you can mitigate or even eliminate the feeling of burning that you are experiencing by cooking.

    Dangerous for Pets

    Dangerous for Pets


    Even though onions are considered beneficial to human health, they are incredibly harmful to the health of certain animals, such as dogs, cats, horses, and monkeys.

    Sulfoxides and sulfides are the main culprits here, as they can cause Heinz's body anemia, a condition caused by consuming these substances. The disease is characterized by damage in the red blood cells of affected animals, resulting in anemia due to the injury.

    The best thing you can do if you have pets in your home is never to give them onions to eat; you should also make sure that anything which is flavored with onions is kept out of their reach if you do.


    It has been reported that some people experience digestive discomfort when they consume onions, and raw onions are also known to irritate some people's eyes, mouths, and skin. According to some evidence, certain animals are toxic to onions.

    Onions Have 9 Impressive Health Benefits

    Onions have 9 Impressive health benefits


     Even though all vegetables are essential for health, certain kinds offer unique benefits.

    The onion belongs to the Allium genus of flowering plants, which includes garlic, shallots, leeks, and chives, all of which are members of the same genus.

    Various vitamins, minerals, and potent compounds can be found in these vegetables, all of which have been shown to promote health in multiple ways.

    Thousands of years ago, onions were used when they were used for treating ailments such as headaches, heart disease, and mouth sores.

    Here are nine impressive health benefits of onions that you should be aware of.

    1. Laden With Vitamins & Minerals

    Vitamins & Minerals, Respectively



    Foods considered nutrient-dense are low in calories; however, they contain a high quantity of essential nutrients such as vitamins and minerals, which are necessary for the body to function correctly.

    Even though one medium onion has only 44 calories, it contains an incredible amount of vitamins, minerals, and fiber essential for the body.

    Vitamin C is an essential nutrient that plays a crucial role in maintaining a healthy immune system, in the production of collagen, in the repair of tissues, and the absorption of iron. This vegetable is exceptionally high in vitamin C.

    The free radicals in the body are unstable molecules that have the potential to damage healthy cells in the body. It is also known that vitamin C acts as a powerful antioxidant in the body, protecting cells from the damage caused by free radicals.

    Vitamins & Minerals, Respectively


    Furthermore, onions are also an excellent source of B vitamins, such as folate (B9) and pyridoxine (B6), which are essential for healthy metabolism, the production of red blood cells, and the maintenance of normal nerve function.

    As a result, they are an excellent source of potassium, which many mineral people lack in their diets due to nutritional deficiencies.

    It is estimated that the average American consumes only slightly more than half of the daily recommended potassium intake, which is 4,700 mg.

    As a nutrient, potassium is essential for maintaining normal cellular function, fluid balance, nerve transmission, kidney function, and the contraction of muscles.


    It is essential to know that onions have a low-calorie count but a high nutrient content, especially in the form of vitamin C, B vitamins, and potassium.

    2. Could Be Good for Your Heart's Health

    Could Be Good for Your Heart's Health


    Many antioxidants and compounds in onions reduce inflammation and triglyceride levels and lower cholesterol levels in the body. As a result of all these factors, the risk of developing cardiovascular disease is reduced.

    As a result of their potent anti-inflammatory properties, they may also be beneficial for lowering high blood pressure and preventing blood clots because of their potent anti-inflammatory properties.

    A flavonoid antioxidant known as quercetin is found in high concentrations in onions, and onions are particularly rich in flavonoids. Because it is an effective anti-inflammatory, it may be able to reduce risk factors for cardiovascular diseases, such as high blood pressure, by reducing inflammation.

    According to a study involving 70 obese people suffering from high blood pressure, a dose of quercetin-rich onion extract at 162 milligrams per day significantly reduced systolic blood pressure by 3–6 millimeters of mercury (mmHg) compared to placebo treatment.

    It has also been demonstrated that onions can lower levels of cholesterol.

    onions can lower levels of cholesterol


    A study involving 54 women with the polycystic ovarian syndrome (PCOS) found that eating raw red onions (40-50 grams/day if overweight and 50–60 grams/day if obese) for eight weeks decreased levels of total and "bad" LDL cholesterol.

    Moreover, there is evidence that eating onions may reduce the risk factors for heart disease, such as inflammation, high triglyceride levels, and the formation of blood clots, as evidenced by studies conducted on animals.


    In some studies, researchers have found that eating onions may reduce some risk factors for cardiovascular diseases, such as high blood pressure, elevated triglyceride levels, and inflammation.

    3. Antioxidant Powerhouse Packed in Full

    Antioxidant Powerhouse Packed in Full


    In a nutshell, antioxidants inhibit the oxidation of oxygen in the body. This process can damage cells and contribute to the onset of diseases such as cancer, diabetes, and heart disease. Several foods and supplements contain antioxidants.

    Undoubtedly, onions are an excellent source of antioxidants, and it is essential to note that they contain over 25 different flavonoid antioxidants in their composition.

    Especially red onions contain anthocyanins, unique plant pigments belonging to the flavonoid family, responsible for giving red onions their dark color. The anthocyanins provide the dark color of red onions.

    Especially red onions contain anthocyanins,


    Several population studies have found that people who consume a diet that is higher in foods rich in anthocyanins have a lower risk of developing heart disease than those who consume a diet that is low in such foods.

    Evidence from one study involving 43,880 male participants showed that regular intakes of anthocyanins at levels as high as 613 mg per day were associated with a 14% lower risk of a nonfatal heart attack compared to those who did not consume anthocyanins.

    Similarly, a study that included 93,600 women found that those who consumed the most foods high in anthocyanins also had a 32% lower risk of having a heart attack compared to women who consumed the fewest foods that were high in anthocyanins.
    It has also been found that anthocyanin consumption can reduce the risk of developing diabetes and certain types of cancer as an additional benefit of consuming these substances.

    Several powerful plant pigments, called anthocyanins, are abundant in red onions. Anthocyanins have been proven to protect against coronary heart disease, certain cancers, and diabetes, and some evidence supports this claim.

    4. Compounds That Fight Cancer That They Contain

    Compounds That Fight Cancer That They Contain


    According to some studies, consuming foods from the Allium genus, such as garlic and onions, has been associated with a reduced risk of developing several types of cancer, including stomach and colorectal cancer.

    Compared to people who consumed the least amount of allium vegetables, those who consumed the most had a 22% lower risk of developing stomach cancer, according to a review of 26 studies that examined the effects of allium vegetables on stomach cancer diagnosis.

    A review of 16 studies that included 13,333 participants found that those who ate the most had a 15% lower risk of colorectal cancer than those who ate the smallest onions. As a result of the participants' consumption of onions, this finding was reached.

    According to research, these cancer-fighting properties of allium vegetables can be attributed to the sulfur compounds and flavonoid antioxidants found in these vegetables.

    One of these compounds found in onions is called onion A, which contains sulfur, which in test-tube research, has been shown to inhibit the growth of tumors and slow the spread of cancers such as ovarian and lung cancers.

    Onions also contain the flavonoid antioxidants fisetin and quercetin, which may have the ability to prevent the growth of tumors in the body.


    Various studies have found that eating a diet high in allium vegetables, such as onions, may reduce the risk of certain cancers in some people.

    5. Contribute to The Regulation of Blood Sugar

    Contribute to The Regulation of Blood Sugar


    It has been found that onions may aid in controlling blood sugar levels, which is especially important for people who have diabetes or are at risk of becoming diabetic.

    There was a significant reduction in fasting blood sugar levels after four hours of consuming 3.5 ounces (100 grams) of fresh red onions in a study of 42 people with type 2 diabetes that involved the consumption of 3.5 ounces (100 grams) of fresh red onions.

    Additionally, in several scientific studies conducted on animals, there has been evidence that the consumption of onions may have a beneficial effect on regulating blood sugar levels.

    Diabetic rats fed food containing 5% onion extract for 28 days had significantly lower fasting blood sugar and body fat levels than rats fed regular diets.

    Onions contain several different compounds, some of which are known to have anti-diabetic properties. A few of these compounds include quercetin and compounds containing sulfur.

    As an example, it has been demonstrated that quercetin can be beneficial in regulating blood sugar levels throughout the body due to its interaction with cells in the small intestine, pancreas, skeletal muscle, fat tissue, and liver.


    There is evidence that onions may help lower high blood sugar levels because they contain several compounds with several health benefits.

    6. May Cause an Increase in Bone Density

    May Cause an Increase in Bone Density


    Even though dairy products are most often credited with improving bone health, many other foods, such as onions, may also assist in maintaining a healthy bone structure.

    A study involving 24 women of middle age and postmenopausal women showed that those who consumed 3.4 ounces (100 ml) of onion juice every day for eight weeks had improved bone mineral density and antioxidant activity compared to a group that served as the control group. Over eight weeks, the study was conducted.

    Five hundred-seven perimenopausal or postmenopausal women who ate onions daily had greater bone density than those who ate onions only once a month. As a result of the daily consumption of onions.
    The research found that older women who consumed onions regularly had a risk of hip fracture that was more than 20% lower than those who did not consume onions regularly.

    A recent study found that onions reduced oxidative stress, increased antioxidant levels, and decreased bone loss, all of which may contribute to the prevention of osteoporosis and boost bone density.


    There is a correlation between eating onions and having a higher bone mineral density, according to some studies that have been conducted.

    7. Have the Capability to Fight Bacteria

    Have the Capability to Fight Bacteria


    As a result of onions' antibacterial properties, they are effective against a wide range of bacteria, including Escherichia coli (E. coli), Pseudomonas aeruginosa, Staphylococcus aureus (S. aureus), and Bacillus cereus.

    Additionally, research has shown that onion extract can inhibit the growth of Vibrio cholerae, a type of bacteria regarded as a significant cause of concern in terms of public health in developing countries.

    There seems to be a particularly effective method of preventing bacteria from multiplying in the body using quercetin extracted from onions.
    The growth of Helicobacter pylori (H. pylori) and Methicillin-resistant Staphylococcus aureus (MRSA) was successfully inhibited by quercetin extracted from yellow onion skin, according to the results of an experiment conducted in test tubes (MRSA).

    H. Pylori is a type of bacteria linked to stomach ulcers, and certain types of cancers of the digestive system are found in the stomach. As opposed to MRSA, an antibiotic-resistant bacteria that can cause infections in various parts of the body, MRSA is an infection-causing bacteria.

    As part of another study conducted in test tubes, quercetin was found to damage the cell membranes and walls of E. coli. coli as well as S. aureus.


    Onions are effective at preventing the growth of potentially harmful bacteria, such as E. coli. Coli and S. aureus.

    8. Could be Beneficial to Digestive Health

    Could be Beneficial to Digestive Health


    A significant amount of fiber is contained in onions and prebiotic compounds, essential for maintaining a healthy digestive system.

    There are beneficial bacteria that inhabit the digestive tract that is responsible for breaking down prebiotics, which are forms of fiber that humans cannot digest.
    As a result of bacteria feeding on prebiotics, short-chain fatty acids are produced in the intestines. This group has three acids: acetate, propionate, and butyrate.

    There is evidence to suggest that these short-chain fatty acids are beneficial to digestion, gut health, immunity, and inflammation reduction, as well as digestive discomfort, according to research.

    Prebiotics are also known to increase the production of beneficial probiotic strains, such as Lactobacillus and bifidobacterial, which are suitable for the digestive system when consumed in foods high in prebiotics.

    A diet high in prebiotics may help improve the body's absorption of essential minerals, such as calcium, which may enhance the bones' health.

    There are two types of prebiotics that you can find in abundance in onions: inulin and fructooligosaccharide, which are both types of prebiotics. They help to increase the number of beneficial bacteria in your gut, which improves your immune system's function by increasing the number of healthy bacteria in your heart.


    A high concentration of prebiotics can be found in onions, which are beneficial for your digestive system since they help increase the balance of bacteria in your gut and boost the immune system.

    9. Simple to Incorporate Into Your Diet

    Simple to Incorporate Into Your Diet


    Onions are a common ingredient found in kitchens all over the world.

    As well as imparting flavor to savory dishes, they can also be eaten raw or cooked, depending on your preference.

    Not to mention the fact that they can increase your intake of fiber, vitamins, and minerals, in addition to the fact that they can improve your digestion.

    You Can Incorporate Onions Into Your Diet in The Following Ways:

    • You can give your guacamole recipe a little kick by using raw onions.
    • To sweeten savory baked goods, add onions that have been caramelized.
    • Mix cooked onions with other vegetables for a tasty and nutritious side dish.
    • Egg dishes, such as omelets, frittatas, and quiches, can benefit from adding onions that have been cooked.
    • Onions that have been sautéed can be served on top of meat, chicken, or tofu.
    • Add some red onions that have been sliced very thinly to your favorite salad.
    • You can use chickpeas, chopped onions, and chopped red pepper
      to make a salad that is high in fiber.
    • When making stocks and soups, onion and garlic make excellent foundational ingredients.
    • Stir-fry dishes benefit from the addition of onions.
    • To embellish tacos, fajitas, and other Mexican dishes, chop raw onions and sprinkle them on top.
    • You can use fresh onions, tomatoes, and cilantro to make a delicious homemade sauce.
      Make a hearty soup with onions, vegetables, and other vegetables.
    • To enhance the flavor of your chili recipes, try adding onions.
    • Create a delicious homemade salad dressing combining raw onions, fresh herbs, vinegar, and olive oil in a blender.


    Due to their versatility and ease of use, You can add onions to various dishes, including eggs, guacamole, meat dishes, soups, and baked goods.

    The Bottom Line

    The Bottom Line


    The number of ways onions can improve one's health is genuinely remarkable.

    In addition to being loaded with vitamins and minerals, these nutrient-dense vegetables contain compounds that have been proven to lower the risk of certain cancers and cardiovascular diseases.

    The properties of onions have been shown to inhibit the growth of bacteria and improve the digestive system's health, which may contribute to an improved immune system.

    Furthermore, they are adaptable and can be used in various ways to enhance the flavor of different savory dishes in varying intensities.

    One simple step to improve your overall health is to increase the number of onions in your diet.
    One of the best things about onions is that they are a type of root vegetable with several valuable properties.



    There is a high concentration of antioxidants and sulfur-containing compounds in these foods, some of which have the potential to exert various beneficial effects on the body.

    Onions have been linked to improved bone health, lower blood sugar levels, and a reduced risk of cancer; however, additional research is still needed.

    It should be noted, however, that they may also cause digestive problems in some people.

    Doubtless, onions are a healthy food to include in your diet if you enjoy eating them and feel that they are a part of your diet.

    Onions have several impressive health benefits that can be attributed to them.

    Even though all vegetables are beneficial to the health of one's body, some types of vegetables offer additional advantages.

    some types of vegetables offer additional advantages.


    Among the other flowering plants that belong to the Allium genus of plants, which also includes onions, garlic, shallots, leeks, and chives, are the cloves of garlic, shallots, leeks, and chives.

    It has been found that these vegetables are packed with many vitamins, minerals, and potent plant compounds that can be beneficial to one's health in different ways depending on how they are eaten.
    Especially onions because it contains onion calories.

    Onions have been used medicinally for quite a while to treat ailments such as headaches, heart disease, and mouth sores, indicating that their medicinal properties have been known for quite a bit.

    Frequently Asked Questions