How many calories are in an onion?

A medium onion (110g) has 44 calories. Per 100g, onions are 40 calories, which is very low for a vegetable. One cup chopped has 64 calories. Raw and cooked onions have similar calorie counts.

Are onions good for weight loss?

Onions are excellent for weight loss at only 40 cal/100g. They add significant flavor to dishes without adding many calories, helping make healthy meals more satisfying. The 1.7g fiber aids fullness.

What nutrients are in onions?

Onions provide 146mg potassium, 7mg vitamin C, and 1.1g protein per 100g. They're also rich in quercetin (a powerful antioxidant) and sulfur compounds that support immune function and heart health.

Are onions keto-friendly?

Onions are moderately keto-friendly with 7.6g net carbs per 100g (9.3g carbs - 1.7g fiber). Use them sparingly as a flavor base - 1/4 cup chopped adds only 3g net carbs to a dish.

Do onions have health benefits?

Onions contain quercetin and sulfur compounds with anti-inflammatory and antioxidant properties. Studies link regular onion consumption to lower blood pressure, reduced cholesterol, and decreased cancer risk.

Which type of onion is healthiest?

Red onions have the most antioxidants (especially quercetin), followed by yellow, then white. Shallots are even higher in antioxidants per gram. All types have similar calories (40 cal/100g) and benefits.

Are raw onions healthier than cooked?

Raw onions retain more vitamin C and some antioxidants. However, cooking makes other nutrients more bioavailable and reduces compounds that cause digestive upset. Both have benefits - vary your intake.

Do onions have sugar?

Onions contain about 4.2g sugar per 100g, which caramelizes when cooked, creating sweetness. This natural sugar is minimal and shouldn't concern most people. Diabetics can enjoy onions freely.

How should I store onions?

Store whole onions in a cool, dry, dark place with good ventilation for 2-3 months. Don't refrigerate whole onions (causes them to soften). Cut onions should be refrigerated and used within 7-10 days.

How much onion can I eat per day?

There's no strict limit - onions are very low calorie and nutritious. Half a medium onion daily provides health benefits without excessive sulfur compound intake that might cause digestive issues in sensitive people.

All Foods

Calories in Onion

USDA Verified · FDC 170000 · Jan 2026

44 calories

per 1 medium onion (110g)

1.1g

Protein

9.3g

Carbs

0.1g

Fat

1.7g

Fiber

Per 100g raw

Log Onion in one photo

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