Onion: Calories, Nutrition Facts, and Health Benefits (2026)

Onions contain 44 calories per medium onion (110 g), with 1.2 g of protein and 10.3 g of carbohydrates. They provide 1.9 g of fiber and 8.1 mg of vitamin C, contributing to 9% of the daily value.

This page explores the nutritional profile of onions, focusing on a medium onion weighing 110 g and its values per 100 g. It also examines how onions fit into various dietary goals and their impact on blood sugar levels.

Onion Nutrition Facts (Per Serving and Per 100 g)

The following nutrition facts table provides detailed information on the composition of onions, highlighting key nutrients and their contributions.

Values are for 1 medium onion (110 g).

Nutrient	Per Serving	Per 100 g	% Daily Value (per serving)
Calories	44	40	2%
Protein	1.2 g	1.1 g	2%
Carbohydrates	10.3 g	9.3 g	4%
Fiber	1.9 g	1.7 g	7%
Sugar	4.7 g	4.2 g	-
Fat	0.1 g	0.1 g	0%
Vitamin C	8.1 mg	7.4 mg	9%
Potassium	161 mg	146 mg	3%
Folate	21 mcg	19 mcg	5%

About 88% of onion calories come from carbohydrates, 10% from protein and 2% from fat.

Onion by Health Goal

In this section, we evaluate how onions rate against common dietary goals, helping you understand their benefits in various contexts.

Goal	Rating	Why
Weight loss	Excellent	44 calories per serving with 1.9 g fiber for fullness
Blood sugar / diabetes	Excellent	Glycemic load of about 2 per serving
Immunity	Fair	Provides 8.1 mg vitamin C (9% DV)
Digestion	Fair	1.9 g fiber per serving supports regularity
Heart health	Good	Potassium (161 mg) and fiber, very low sodium
Muscle gain	Fair	Low in protein (1.2 g); best as a vitamin-rich choice, not a protein source

Onion and Blood Sugar

Glycemic index: 15. Glycemic load: 2 per serving.

Onion has a glycemic index of about 15 and a glycemic load of around 2 per serving, so it has a modest effect on blood sugar. Fiber and water slow sugar absorption, and pairing it with protein or fat steadies the response.

How Onion Compares to Other Vegetables

The comparison table illustrates how onions stack up against other vegetables in terms of nutritional content, offering a broader perspective on their health benefits.

Vegetable (per 100 g)	Calories	Sugar (g)	Fiber (g)	Vitamin C (mg)
Onion	40	4.2	1.7	7.4
Garlic	149	1.0	2.1	31.2
Leek	61	3.9	1.8	12.0
Shallot	72	7.9	3.2	8.0

Onion Myths, Checked

A cut onion absorbs bacteria from a room , False. A cut onion does not draw germs from the air; just refrigerate leftovers.

Raw onions are much healthier than cooked , Misleading. Raw keeps more vitamin C, but cooked onions still provide fiber and antioxidants.

How to Track Onion

Vegetable portions and cooking method both change the numbers, so the same onion can look very different once it is on your plate. Nutrola identifies food from a photo, barcode or voice entry and returns calories and macros, so you can log onion accurately instead of estimating. Nutrola is available from EUR 2.50 per month and shows no ads on any tier.

For related references, see vegetables ranked by nutrient density, highest-protein vegetables ranked, and lowest-carb keto vegetables ranked.

Sources

Nutrition values are from the USDA FoodData Central database, shown per serving and per 100 g, rounded. Percent Daily Values use US reference intakes for a 2,000 calorie diet. Glycemic index and load are from published international tables and vary by variety, ripeness and cooking method. This is educational and not medical advice.

Frequently Asked Questions (FAQ)

How many calories are in a medium onion?

A medium onion (110 g) contains 44 calories. This low-calorie count makes it a suitable addition to various dishes without significantly increasing overall caloric intake.

Is onion good for weight loss?

Onions can support weight loss efforts due to their low calorie and high fiber content. With 1.9 g of fiber per medium onion, they can help promote satiety.

Can people with diabetes eat onion?

People with diabetes can include onions in their diet, as they have a low glycemic index of about 15. This means they have a minimal impact on blood sugar levels.

How much vitamin C is in onion?

Onions provide 8.1 mg of vitamin C per medium onion, which is about 9% of the daily value. This vitamin is essential for immune function and skin health.

Is onion high in sugar?

Onions contain 4.7 g of sugar per medium onion, which is relatively low. This sugar content is naturally occurring and not the same as added sugars found in processed foods.

Do onions lose nutrients when cooked?

Onions may lose some nutrients when cooked, but they still retain a significant amount of their vitamins and antioxidants. Cooking can also enhance their flavor and digestibility.

Key Takeaways

• Onions have 44 calories per medium serving.
• They contain 1.2 g of protein and 10.3 g of carbs.
• Onions provide 1.9 g of fiber, aiding digestion.
• They are a source of 8.1 mg of vitamin C, about 9% DV.
• Onions have a low glycemic index of 15.
• They contain 4.7 g of sugar per medium onion.