Onion Nutrition Facts: Complete Nutritional Profile Revealed

One medium onion (110g) delivers just 44 calories while providing 20% of your daily vitamin C needs, 10% of vitamin B6, and powerful antioxidants like quercetin. Onions contain zero fat, offer 1.9g of fiber, and deliver unique sulfur compounds that support heart health and inflammation reduction. This complete nutritional breakdown reveals exactly how onions contribute to a balanced diet.

When you reach for onions in your kitchen, you're grabbing one of nature's most nutritionally versatile vegetables. Beyond their culinary importance, onions pack a surprising nutritional punch that many home cooks overlook. Understanding their precise nutritional composition helps you maximize health benefits while enjoying their distinctive flavor in everyday cooking.

Onion Nutrition Fundamentals: What's Inside Your Bulb

Onions belong to the Allium family, sharing genetic ties with garlic, leeks, and chives. Their nutritional profile remains impressive despite their low-calorie count. A single medium onion (approximately 110 grams) contains:

• 44 calories
• 10.3 grams of carbohydrates
• 1.9 grams of dietary fiber (7% of daily value)
• 1.2 grams of sugar
• 1.2 grams of protein
• Negligible fat content

Unlike many vegetables, onions maintain their nutritional integrity whether consumed raw or cooked, though certain preparation methods enhance specific nutrient availability. The USDA FoodData Central database confirms that onions rank among the top vegetable sources of quercetin, a flavonoid antioxidant with significant health implications.

Nutrient	Amount per 100g	% Daily Value
Calories	40 kcal	2%
Carbohydrates	9.3g	3%
Dietary Fiber	1.7g	6%
Vitamin C	7.4mg	12%
Vitamin B6	0.12mg	7%
Folate	19μg	5%
Potassium	146mg	4%
Manganese	0.13mg	6%

Key Nutrients and Their Health Impact

Onions deliver several critical nutrients that contribute to overall wellness. Let's examine the most significant components and their proven health effects.

Vitamin C: Beyond Immunity Support

While commonly associated with immune function, vitamin C in onions serves multiple purposes. One medium onion provides approximately 20% of your daily vitamin C requirement. Research from the National Institutes of Health confirms that vitamin C acts as a powerful antioxidant, protecting cells from free radical damage while supporting collagen production for healthy skin and connective tissues. Unlike citrus fruits, onions maintain their vitamin C content during storage, making them a reliable year-round source.

Quercetin: The Onion's Super Antioxidant

Onions rank among the highest dietary sources of quercetin, particularly red onions which contain up to 36.5mg per 100g according to a comprehensive study published in Molecules. This flavonoid demonstrates remarkable anti-inflammatory properties and may help reduce blood pressure. The unique sulfur compounds in onions work synergistically with quercetin, enhancing its bioavailability when consumed as part of whole food rather than supplements.

Practical Nutrition: Maximizing Onion Benefits

Understanding how preparation methods affect nutritional value helps you make informed cooking decisions. Scientific research reveals important context boundaries for onion nutrition:

Raw vs. Cooked: Nutrient Preservation

Raw onions preserve maximum vitamin C content, but cooking enhances certain antioxidants. A study from the Journal of Agricultural and Food Chemistry demonstrated that boiling onions for 10 minutes increased quercetin availability by 25%, while frying reduced it by 10-20%. For optimal nutrition, consider these preparation guidelines:

• Raw applications: Best for preserving vitamin C and enzyme activity
• Light sautéing: Preserves most nutrients while enhancing flavor
• Long cooking: Increases quercetin bioavailability but reduces vitamin C

Varietal Differences in Nutritional Content

Not all onions offer identical nutritional profiles. Research from the USDA Agricultural Research Service shows significant differences between varieties:

• Red onions: Highest in anthocyanins and quercetin (up to 36.5mg/100g)
• Yellow onions: Most commonly used, with balanced nutrient profile
• White onions: Milder flavor, slightly lower antioxidant content
• Shallots: Highest overall antioxidant capacity among onion varieties

Integrating Onions into a Balanced Diet

Onions complement virtually any dietary pattern, from Mediterranean to plant-based eating. Their versatility makes them valuable for multiple nutritional goals:

• Weight management: Low calorie density with high flavor impact
• Heart health: Sulfur compounds may help lower blood pressure
• Digestive wellness: Prebiotic fiber supports beneficial gut bacteria
• Blood sugar control: Chromium content may improve insulin sensitivity

For maximum nutritional benefit, combine onions with healthy fats like olive oil. The fat-soluble antioxidants in onions become more bioavailable when consumed with dietary fats. Try adding sliced raw onions to salads, lightly sautéing them as a base for soups and stews, or roasting whole bulbs to bring out their natural sweetness while preserving nutrients.

Common Misconceptions About Onion Nutrition

Several myths persist about onion nutrition that deserve clarification based on current scientific understanding:

• "Onions cause acid reflux": While onions may trigger symptoms in sensitive individuals, they don't cause acid reflux in most people. The American College of Gastroenterology notes that individual tolerance varies significantly.
• "Cooking destroys all nutrients": As demonstrated by research, certain preparation methods actually enhance specific nutrients while reducing others.
• "Onions have no protein": While not a protein powerhouse, onions do contribute meaningful amounts to plant-based diets when consumed regularly.

Understanding these nuances helps you make informed decisions about incorporating onions into your diet based on your personal health needs and culinary preferences.

How many calories are in a medium onion?

A medium onion (approximately 110g) contains about 44 calories. This makes onions an excellent low-calorie addition to meals that adds significant flavor and nutritional value without contributing substantially to daily calorie intake.

Which onion variety has the highest antioxidant content?

Red onions contain the highest antioxidant content among common onion varieties, particularly rich in quercetin and anthocyanins. Research shows red onions can contain up to 36.5mg of quercetin per 100g, significantly more than yellow or white onions. Shallots also rank high in overall antioxidant capacity.

Does cooking onions reduce their nutritional value?

Cooking affects different nutrients in various ways. Vitamin C decreases with heat exposure, but certain antioxidants like quercetin become more bioavailable. Light sautéing preserves most nutrients while enhancing flavor, whereas boiling for 10 minutes can increase quercetin availability by 25%. The optimal method depends on which nutrients you want to maximize.

Can onions help lower blood pressure naturally?

Research suggests onions may contribute to healthy blood pressure levels due to their quercetin content and sulfur compounds. A study published in the Journal of Nutrition found that consuming onions regularly was associated with modest reductions in blood pressure, particularly in individuals with hypertension. However, onions should complement rather than replace medical treatment for high blood pressure.

How much onion should I eat daily for health benefits?

While no official daily recommendation exists, consuming approximately ½ to 1 medium onion (55-110g) daily provides significant nutritional benefits without overwhelming your diet. This amount delivers valuable antioxidants, fiber, and vitamins while complementing various dietary patterns from Mediterranean to plant-based eating.