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Onion Calories
Low calorie, source of vitamin C, contains antioxidants
In season: Spring · Summer · Autumn · Winter
CALORIES
GI
POTASSIUM
FIBER
Quick answer
1 piece (medium) of Onion (80 g) has 32 calories. That works out to 40 calories per 100 g. It contains 7.4 g of carbs, 0.9 g of protein, 0.1 g of fat and 1.4 g of fiber. Its 5.9 mg of Vitamin C covers 7% of the Daily Value. Its glycemic index is 15 (low), so it raises blood sugar slowly.
What is Onion?
Onion is a bulb vegetable made up of crisp, layered flesh beneath papery skin. It is used around the world as a base for soups, sauces, stews and many everyday dishes; spring onions are a familiar alternative when their milder greens are wanted too.
Raw onion is juicy and sharp, while cooking softens its bite and brings out a gentle sweetness. Serve it sliced in salads or sandwiches, or cook it slowly with other ingredients to build flavour. Onion is low in calories and contributes fibre and vitamin C, making it an easy way to add flavour to meals. For a milder raw taste, slice it thinly and briefly rinse or soak it in cold water.
Onion Nutrition Facts
Selected: 100 g
40
KCAL / 100G
Carbs
9.3g
· 3% DV
Protein
1.1g
· 2% DV
Fat
0.1g
· 0% DV
Fiber
1.7g
· 6% DV
DV is the share of the daily value covered, on a 2,000 kcal reference diet.
Calories come from: Carbs 88% · Protein 10% · Fat 2%
Onion Vitamins & Minerals
Vitamins
Vitamin C
7.4mg · 8% DV
B6
0.12mg · 7% DV
Folate
19µg · 5% DV
B1
0.04mg · 3% DV
Minerals
Phosphorus
29mg · 4% DV
Potassium ⭐
146mg · 4% DV
Calcium
23mg · 2% DV
Magnesium
10mg · 2% DV
How Nutritious Is Onion?
Nutrient density
High
How many vitamins, minerals and how much fiber this food carries per calorie. A high score means a lot of nutrition for few calories.
Satiety score
Medium
An EatBetter score computed from fiber, protein and calorie density. A high score means staying full longer on the same calories.
Both scores are calculated per 100 g and do not change with the selected portion. The satiety score is EatBetter's own calculation, not a clinical measure.
Onion Glycemic Index
GLYCEMIC INDEX
GLYCEMIC LOAD
Accounts for portion size — a more realistic measure than GI alone.
How to Burn Off Onion
To burn the 40 calories in 100 g:
🚶
Walking (5 km/h)
🏃
Running (8 km/h)
🚴
Cycling
🏊
Swimming
Times are calculated with the MET equation for a 70 kg adult. Actual burn varies with your weight, age and pace.
Is Onion Processed?
NOVA 1
Unprocessed
1. Unprocessed
2. Minimally Processed
3. Processed
4. Ultra-Processed
NOVA classifies foods into 4 groups by industrial processing. NOVA 1 (unprocessed) is the healthiest.
Does Onion Contain Allergens?
No known major allergens
Which Diets Is Onion Good For?
Vegan
✓ Suitable
Vegetarian
✓ Suitable
Gluten-Free
✓ Suitable
Dairy-Free
— Not suitable
Mediterranean
✓ Suitable
Paleo
✓ Suitable
Whole30
— Not suitable
DASH
— Not suitable
Keto
— Not suitable
Low FODMAP
— Not suitable
Onion Fat Profile
SATURATED
0.03g
MONOUNSATURATED
0.01g
POLYUNSATURATED
0.02g
Omega 6:3 ratio 2:1
Below the ideal 4:1 — a good omega balance.
Compare Onion
Foods Similar to Onion
Frequently Asked Questions About Onion
How do you store onions?
Keep whole, dry onions in a cool, dry, well-ventilated place, such as a mesh bag or open basket. Avoid sealed plastic bags and damp areas, which can encourage spoilage.
Why do onions make you cry?
Cutting an onion releases volatile compounds that irritate the eyes and trigger tears. Chilling the onion before cutting, using a sharp knife, and improving ventilation can reduce the irritation.
Can you eat a sprouted onion?
Yes, a sprouted onion is usually safe to eat if it is still firm and has no mold or off smell. Remove the sprout if you prefer; discard onions that are soft, slimy, or spoiled.
Should onions be refrigerated?
Whole, uncut onions generally keep better in a cool, dry, ventilated pantry than in the refrigerator, where moisture can make them spoil sooner. Refrigerate peeled or cut onion in a sealed container.
Can you freeze onions?
Yes, onions freeze well when chopped and packed airtight. Their texture becomes soft after thawing, so use frozen onion in soups, sauces, and cooked dishes rather than fresh salads.
How long does a cut onion last in the fridge?
Store cut onion in a sealed container in the refrigerator and use it within a few days. Throw it away if it develops mold, a slimy surface, or an unpleasant smell.
How do you caramelize onions?
Cook thinly sliced onions slowly over low to medium-low heat with a little oil or butter, stirring occasionally. They need time to soften and turn golden; high heat can burn them before their natural sugars develop.
Are raw onions harder to digest than cooked onions?
Often, yes: raw onion can cause more bloating or discomfort for some people, while cooking softens its pungent compounds. If raw onion bothers you, try a smaller amount or use it cooked.
How can you tell if an onion has gone bad?
A spoiled onion may feel soft or slimy, show mold, or smell unpleasant. A dry outer skin or a small sprout alone does not necessarily mean it has gone bad.
What is the difference between yellow, red, and white onions?
Yellow onions have a balanced, savory flavor and work well in many cooked dishes; red onions are often milder and used raw, while white onions have a sharper taste. These are common tendencies, not strict rules.
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Nutrition data compiled from USDA FoodData Central and scientific sources.