Onion: Nutritional Facts and Health Benefits


Onions, belonging to the Allium family, are one of the oldest cultivated vegetables, cherished for their distinct flavor and numerous health benefits. These layered bulbs are not only a culinary delight but also pack a powerful nutritional punch. From ancient civilizations to modern-day kitchens, onions have held a crucial place in culinary traditions and medicinal practices. In this article, we delve into the nutritional facts and explore the remarkable health benefits that make onions a must-have addition to your diet.

Nutritional Facts

Onions are low in calories and fat, making them a guilt-free addition to your meals. They are primarily composed of water, but the rest of their nutritional profile is equally impressive. A 100-gram serving of raw onion contains approximately:

  1. Calories: 40-45 kcal
  2. Carbohydrates: 9-10 grams
  3. Fiber: 1.7-2.5 grams
  4. Protein: 1.1-1.3 grams
  5. Fat: 0.1-0.2 grams
  6. Vitamin C: 7-10 milligrams (10-13% of the recommended daily intake)
  7. Folate (Vitamin B9): 19-20 micrograms (5-6% of the recommended daily intake)
  8. Potassium: 146-160 milligrams (4-5% of the recommended daily intake)

Onions are also rich in various essential minerals such as manganese, phosphorus, and copper. Additionally, they contain numerous bioactive compounds like quercetin, sulfur compounds (alliin, allicin), and flavonoids, which contribute to their health benefits.

Health Benefits

  1. Immune Support: The high vitamin C content in onions strengthens the immune system, helping the body fight off infections and illnesses. The antioxidants present in onions, particularly quercetin, help reduce inflammation and oxidative stress, supporting overall immune health.
  2. Heart Health: Onions possess heart-friendly properties. The sulfur compounds and flavonoids in onions may help lower LDL cholesterol levels and blood pressure, reducing the risk of cardiovascular diseases. Quercetin, specifically, has been associated with improved heart health by promoting healthy blood vessel function.
  3. Anticancer Properties: Studies suggest that the compounds found in onions, especially quercetin and sulfur compounds, may have anti-cancer effects. These compounds may help inhibit the growth of cancer cells and reduce the risk of certain types of cancer, including stomach, colorectal, and prostate cancer.
  4. Blood Sugar Regulation: Onions contain a compound called allyl propyl disulfide, which has been shown to help lower blood sugar levels. For individuals with diabetes or those at risk of developing diabetes, including onions in their diet can be beneficial in managing blood glucose levels.
  5. Digestive Health: The fiber content in onions aids in digestion and promotes a healthy gut. It supports regular bowel movements, prevents constipation, and promotes the growth of beneficial gut bacteria.
  6. Anti-inflammatory Effects: The presence of quercetin and other antioxidants in onions provides anti-inflammatory benefits, which may help reduce the risk of chronic inflammatory conditions such as arthritis.
  7. Bone Health: Onions are a good source of calcium, which is essential for maintaining strong bones and preventing conditions like osteoporosis.

Do onions produce gas in the bowel?

Yes, onions can produce gas in the bowel. Onions, along with some other vegetables, belong to a group of foods known as FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). FODMAPs are short-chain carbohydrates and sugar alcohols that are not fully absorbed in the small intestine. Instead, they pass into the large intestine where they can be fermented by gut bacteria.

During the fermentation process, gases like carbon dioxide, hydrogen, and methane are produced, leading to the formation of gas in the bowel. This gas can cause bloating, discomfort, and flatulence in some individuals, especially those with irritable bowel syndrome (IBS) or other digestive sensitivities.

Onions contain fructans, which are a type of FODMAP carbohydrate that some people have difficulty digesting. Consequently, if you are sensitive to FODMAPs or have been diagnosed with IBS, consuming onions might exacerbate gastrointestinal symptoms.

Not everyone is affected by FODMAPs to the same extent. Some individuals can tolerate onions and other high-FODMAP foods without any issues, while others may experience discomfort. If you suspect that onions or other FODMAP-containing foods are causing digestive problems, consult a gastroenterologist or a registered dietitian. They can help you identify potential triggers and provide guidance on managing your diet to reduce gastrointestinal symptoms. Additionally, there are ways to cook onions that might reduce their FODMAP content, making them easier to digest for some individuals.

How to cook onions to reduce their FODMAP content?

Cooking onions can help reduce their FODMAP content, making them more tolerable for individuals with sensitivities to these carbohydrates. The process of cooking breaks down the complex carbohydrates in onions, including fructans, into simpler forms that are easier to digest. Here are some cooking methods that can help reduce the FODMAP content in onions:

  1. Sautéing: Cooking onions over medium heat with a little bit of oil can help break down the FODMAPs. Avoid cooking them until they are deeply browned, as this may cause the FODMAP content to increase again.
  2. Boiling: Boiling onions in water can help leach out some of the FODMAPs. You can use the boiled onions in soups, stews, or other dishes.
  3. Pickling: Pickling onions in a solution of vinegar, water, and spices can reduce their FODMAP content. This process can also add a tangy flavor to the onions, making them a great addition to salads or sandwiches.
  4. Microwave: Microwaving onions can be a quick way to soften them and reduce FODMAPs. Place the chopped onions in a microwave-safe dish with a little water, cover it, and microwave on high for a few minutes until the onions are tender.
  5. Use only the green parts of green onions: The green parts of green onions (spring onions or scallions) are lower in FODMAPs compared to the white bulbs. So, if you enjoy the flavor of onions but want to minimize FODMAPs, opt for the green parts only.

While these cooking methods can help reduce the FODMAP content in onions, they may not eliminate them entirely. The tolerance to FODMAPs varies from person to person, so listen to your body and adjust your diet accordingly. If you have severe FODMAP sensitivities or digestive issues, consider working with a registered dietitian who can help you create a personalized low-FODMAP meal plan while ensuring you still get a balanced and nutritious diet.

Bottom line

As a staple ingredient in countless recipes, onions not only enhance the flavor of dishes but also offer a myriad of health benefits. From bolstering the immune system to supporting heart health and aiding in digestion, the nutritional components in onions make them a potent superfood. Embrace the versatility of onions by incorporating them into your daily meals, and savor both the taste and health benefits of this remarkable vegetable. However, it is essential to remember that while onions are generally safe for most people, individuals with onion allergies or specific medical conditions should consult a gastroenterologist before making significant changes to their diet.

How can I contact gastroenterologist Dr. Zavos for an appointment?

Dr. Chris Zavos is a board-certified gastroenterologist and hepatologist, located in Thessaloniki Greece, and specifically in Kalamaria suburb, about 7 kilometres (4 miles) southeast of downtown Thessaloniki. His private office is at: Fanariou 8 street (near Aigaiou and Adrianoupoleos avenues), Kalamaria (Thessaloniki), Greece.

Thessaloniki International Airport is only 10 km away from his private office in Kalamaria and can be reached by taxi within 13 minutes from the airport.

Dr. Chris Zavos performs endoscopies at Bioclinic private hospital in downtown Thessaloniki (Mitropoleos 86 street).

You can contact Dr. Zavos at phone numbers: (+30)-6976596988 and (+30)-2311283833, or you can email him at czavos@ymail.com. Dr. Zavos responds to Greek and English languages.

Last update: 26 September 2023, 19:07


Gastroenterologist - Hepatologist, Thessaloniki

PhD at Medical School, Aristotle University of Thessaloniki, Greece

PGDip at Universitair Medisch Centrum Utrecht, The Netherlands

Ex President, Hellenic H. pylori & Microbiota Study Group