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Onions - Nutrition, Health Benefits, and Side Effects

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Onions are an imperative ingredient for most of the main course dishes. Read the article below to learn about them more.

Written by

Dr. Zeba Jabeen

Medically reviewed by

Dr. Achanta Krishna Swaroop

Published At September 14, 2022
Reviewed AtApril 4, 2023

What Are Onions?

Onions are a member of the lily (Liliaceae) family, besides garlic, shallots, and leeks. After garlic, they are the next valued vegetable because of their powerful components that benefit health in a million ways. Onions are also used as a basic ingredient in a plethora of dishes. They can be consumed in raw form, sauteed, baked, steamed, or boiled.

What Is the Nutritional Profile of Onions?

Onions have a rich nutritional profile that offers unique properties to them. An 80 g portion (one medium onion) of raw onion provides:

  • 28 kcal/120 kj of energy.

  • 0.8 g proteins.

  • 6.4 g carbohydrates.

  • 5 g sugar.

  • 1.8 g fiber.

  • 2 mg vitamin C.

What Are the Health Benefits of Onions?

Onions render a wide range of benefits to almost all parts of the body. Some of them are listed as:

Rich in Antioxidants: Onions are packed with plant chemicals like flavonoids, which hold both antioxidant and anti-inflammatory effects. When taken regularly and in adequate quantities, the compounds in onion help protect against chronic conditions like cancer and diabetes. As a fact, onions possess more than 25 different flavonoids and are one of their richest sources taken in the diet. Onions also carry sulfur-containing compounds, which have been proven to provide protection against some cancers.

Assists Heart Health: A flavonoid in onions called quercetin has protective antioxidative and anti-inflammatory properties and makes it a heart-friendly vegetable. Studies claimed that eating onions reduces the risk of cardiovascular diseases by decreasing blood pressure, managing blood cholesterol levels, and reducing inflammation. The older and stored onions have stronger characteristics. Quercetin also has the power to inhibit Helicobacter pylori growth and also of Methicillin-resistant staphylococcus aureus (MRSA).

Aids Bone Health: Incorporating onions into the diet is linked to enhanced bone density. This may be attributed to their antioxidative effects, which decrease oxidative stress and eventually reduce bone loss. Research on middle-aged women found that onion juice decreases bone loss and improves bone density.

Promotes Gut Health: Onions are loaded with fiber, particularly the non-digestible form that is essential for good gut health. Although humans cannot digest prebiotic fiber, it is beneficial to the good bacteria in the gut which uses it to produce by-products known as short-chain fatty acids (SCFAs). These SCFAs are imperative for maintaining gut health and its integrity and support immunity and digestion.

Possess Antibacterial Characteristics: Onions are used in ayurvedic medicine and home remedies for coughs, colds, etc. As per the studies, onions have remarkable antibacterial properties against bacteria such as escherichia coli, pseudomonas aeruginosa, and staphylococcus aureus.

What Are the Side Effects of Onions?

Along with abundant health benefits, onions carry some possible side effects too. They are as follows:

Decreases Blood Sugar Levels: Onions reduce blood glucose levels, so they are beneficial for diabetics yet, they should consume them with care, especially those diabetes medications, as onions might decrease their blood sugar levels too much.

Gastric Burning: Onions are used in the treatment of many gastrointestinal disorders. However, their excess intake may lead to gastric irritation, vomiting, nausea, and burning.

Skin Irritation: Although onions are claimed to enhance skin health, certain people may experience face or skin irritation and rashes on the application of onion juice to their skin. So, a small patch test is advised on a small area of the skin prior to its application.

Heartburn: Excess consumption of onion can cause heartburn. They can lead to side effects in patients with heart diseases. However, such cases demand immediate medical attention. In pregnant and nursing women, this effect is enhanced so care is needed for them too.

Bad Breath: Onions leave a foul odor in the mouth after their consumption because of their strong and slightly pungent aroma, which is due to their high content of sulfur.

Reduces Blood Pressure: Onions may decrease both systolic and diastolic blood pressure. Thus, those taking medications for hypertension should take cautions in their intake.

Possess Anticoagulant Property: Onion use may inhibit blood clotting because of its anticoagulant characteristic. Having them along with anticoagulant drugs increases the risk of bleeding and bruising. Hence, one should have information on this critical adverse effect of onion consumption.

Increased Sensitivity: Certain individuals may have an allergy to onions. Such people should not take Aspirin and onion together as Aspirin enhances onion sensitivity.

Increased Lithium: Onions may reduce the capacity of the body to eliminate lithium out of the body. So, it is advised to consult a registered doctor before starting any lithium-containing drugs in conjunction with consuming onions.

Are Onions Safe for Everyone to Consume?

Certain individuals may develop an allergy to onions and are sensitive to them. They experience digestive problems, like heartburn and flatulence. Onions comprise FODMAPs, a kind of carbohydrate and fiber that is not tolerable by the digestive system in them.

How to Select and Store Onions?

The most commonly available onions are globe onions, which should be clean and hard and should have dry and smooth peels. Decaying onions and those with a developed seed stem should be avoided. Onions should be kept at room temperature, in a well-ventilated area, away from bright light. The onions with a more pungent flavor, like yellow onions, have a longer shelf-life than those with a sweeter taste, like white onions, as the compounds producing the sharp taste are natural preservatives themselves.

Onions should be stored at a distance from potatoes, because onions may absorb their moisture and ethylene gas, decreasing the shelf-life of potatoes. Cooked onions should not be stored in a metal bowl or in a metal storage container, as they may get discolored. Freezing the cut and chopped onions makes them lose much of their flavor.

The compound allyl sulfate, which gets produced when onion ruptured cells come in contact with air, produces tears. To decrease the production of this compound and easy handling of onions, they should be chilled for approximately 30 minutes prior to cutting them to decrease the enzyme activity.


Onions are a must-have vegetable in the kitchen. Not only do they add a touch of sweet taste to the food but they are preferred for their bountiful health benefits as well. In certain situations, they need to be limited, so they should be consumed while keeping their adverse effects in mind.

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Dr. Achanta Krishna Swaroop
Dr. Achanta Krishna Swaroop



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