Calories in an Onion: Full Nutrition Breakdown
How many calories are in an onion? Size-by-size breakdown with full nutrition facts and FAQ.
Onions are a culinary staple found in nearly every cuisine around the world. Beyond their flavor, onions are a good source of vitamin C, B vitamins, and potassium. They are also rich in quercetin, a flavonoid antioxidant with anti-inflammatory properties. Onions are low in calories and provide a modest amount of fiber. Here is a complete breakdown of onion nutrition by size.
Calories by size:
| Size | Weight | Calories | Carbs | Fiber | Sugar | Vitamin C |
|---|---|---|---|---|---|---|
| Small | ~70 g | 28 kcal | 6.5 g | 1.2 g | 3 g | 5 mg |
| Medium | ~110 g | 44 kcal | 10 g | 1.9 g | 4.7 g | 8 mg |
| Large | ~150 g | 60 kcal | 14 g | 2.6 g | 6.4 g | 11 mg |
| 1 cup chopped | ~160 g | 64 kcal | 15 g | 2.7 g | 6.8 g | 12 mg |
| 1 slice (thick) | ~38 g | 15 kcal | 3.5 g | 0.5 g | 1.6 g | 3 mg |
Onions also contain small amounts of calcium, iron, folate, and manganese. Red onions tend to have higher antioxidant levels than white or yellow varieties.
Frequently Asked Questions (FAQ)
How many calories are in a medium onion?
A medium yellow onion weighing about 110 grams contains approximately 44 calories. Most of the calories come from carbohydrates — about 10 grams total, of which 4.7 grams are natural sugars and 1.9 grams are dietary fiber. Onions contain virtually no fat and minimal protein.
Are onions good for you?
Onions are very good for you. They are rich in quercetin, a powerful antioxidant that may help reduce inflammation, lower blood pressure, and support heart health. Onions also contain compounds called organosulfur compounds that have been studied for their potential anti-cancer properties.
Do different colored onions have different nutrition?
The nutritional differences between onion varieties are modest but notable. Red onions contain the highest levels of quercetin and anthocyanins (antioxidants), while yellow onions have the highest total flavonoid content. White onions tend to be milder in flavor and slightly lower in antioxidants, though all varieties are nutritious.
Are onions high in sugar?
Onions contain more natural sugar than many vegetables — about 4.7 grams in a medium onion. This sugar becomes more noticeable when onions are caramelized, as the cooking process concentrates the sugars. However, the total calorie count remains low, and onions have a low glycemic index.
Do cooked onions have more calories than raw onions?
Cooked and raw onions have the same calories per gram. However, because onions shrink considerably during cooking as they lose water, a cup of cooked onions contains more onion by weight than a cup of raw onions, and therefore more calories. A cup of sauteed onions has about 115 calories compared to 64 calories for a cup of raw chopped onions.
How many calories are in a medium onion?
Are onions good for you?
Do different colored onions have different nutrition?
Are onions high in sugar?
Do cooked onions have more calories than raw onions?
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