How Many Calories Are in 50g of Red Onion?

November 23, 2025 •

3 min read

According to nutritional data, a 50g serving of raw red onion contains approximately 19 to 21 calories. This makes red onion a low-calorie, flavorful addition to a variety of dishes, offering nutritional benefits with minimal caloric impact, which is ideal for those managing their weight.

Quick Summary

A 50-gram serving of raw red onion contains just 19-21 calories, predominantly from carbohydrates. It also provides essential nutrients like fiber, Vitamin C, and antioxidants, making it a very low-energy yet health-beneficial food item.

Key Points

Low Calorie: A 50g serving of raw red onion contains approximately 19-21 calories.
Rich in Antioxidants: Contains powerful flavonoids like quercetin and anthocyanins, which contribute to its health benefits.
Supports Heart Health: The antioxidants in red onion may help lower blood pressure and cholesterol.
Source of Fiber: Provides nearly 1 gram of dietary fiber per 50g, aiding in digestion.
Promotes Gut Health: Contains prebiotics, such as fructans, that feed beneficial gut bacteria.
Versatile Ingredient: Easily incorporated into various dishes, both raw and cooked, to add flavor and nutrients.

Calorie and Macronutrient Breakdown for 50g of Raw Red Onion

For a standard 50-gram serving of raw red onion, the calorie count is notably low, averaging around 20 calories. Its macronutrient composition consists mainly of carbohydrates, with minimal protein and virtually no fat. This makes it an excellent ingredient for adding flavor without significantly increasing your meal's energy content.

Macronutrients in 50g of Raw Red Onion

Carbohydrates: Approximately 4.7 grams, with about half of this coming from natural sugars and the other portion from dietary fiber.
Protein: Around 0.6 grams, contributing a small amount to your daily protein intake.
Fat: A negligible amount, typically less than 0.1 grams, making it virtually fat-free.
Dietary Fiber: About 0.9 grams, which is beneficial for digestive health and helps promote feelings of fullness.

Rich in Vitamins, Minerals, and Antioxidants

Beyond its basic macronutrient profile, red onion is a nutritional powerhouse packed with beneficial compounds. It is a good source of several vitamins and minerals that support overall health.

Vitamin C: This potent antioxidant is crucial for immune function, collagen production, and iron absorption. While some Vitamin C can be lost during cooking, a raw red onion retains most of this valuable nutrient.
B Vitamins: Red onions contain B vitamins, including folate (B9) and Vitamin B6, which are vital for metabolism and red blood cell formation.
Potassium: This essential mineral plays a key role in maintaining fluid balance, nerve transmission, and heart health.
Antioxidants: The vibrant red-purple color of red onions comes from anthocyanins, powerful antioxidants that may help protect against heart disease. Red onions are also particularly high in quercetin, a flavonoid antioxidant with anti-inflammatory and potential anticancer properties.

Impact of Cooking: Raw vs. Cooked Red Onion

The calorie content of red onion is minimally affected by basic cooking methods like sautéing or roasting, as long as little to no oil is added. However, the nutritional profile can change depending on preparation.

Cooking: Heat can destroy some heat-sensitive nutrients, like a portion of the Vitamin C. However, some studies suggest that the bioavailability of antioxidants like quercetin can be enhanced through certain cooking methods. Caramelizing onions, which involves heating them with some fat, will concentrate their natural sugars and will raise the overall calorie count of the dish.
Raw: Eating red onion raw in salads or salsas ensures you get the maximum amount of its vitamins and sulfur compounds, which contribute to many of its health benefits.

Comparison of Onion Varieties (Per 50g Raw)

While all onions are low in calories and beneficial, there are subtle differences in their nutritional content and antioxidant levels.


Feature	Red Onion (approx. 50g)	Yellow Onion (approx. 50g)	White Onion (approx. 50g)
Calories	19-21 kcal	~20-21 kcal	~16 kcal
Carbohydrates	4.7-5g	~5.1g	~4g
Fiber	~0.9g	~0.7g	~0.5g
Main Antioxidant	Quercetin and Anthocyanins	High in Quercetin	Lower Antioxidant Content

Tips for Incorporating Red Onion into Your Diet

Given its low calorie count and nutrient-dense profile, red onion is a versatile vegetable that can be added to many dishes. Here are a few simple ideas:

Add to Salads: Thinly slice raw red onion for a crisp, colorful, and pungent addition to green salads.
Homemade Salsa: Dice red onion and mix with tomatoes, jalapeños, and cilantro for a fresh, flavorful salsa.
Pickled Onions: Make a quick pickle with red onion, vinegar, and sugar to use as a tangy garnish for tacos and sandwiches.
Roasted Vegetables: Toss chunks of red onion with other vegetables like bell peppers and zucchini, then roast with a drizzle of olive oil.
Burger Topping: Add a slice of raw or grilled red onion to your burgers or sandwiches for extra crunch and flavor.

Conclusion

In summary, a 50g serving of red onion contains a minimal number of calories, making it a fantastic, low-energy food choice. This small portion provides a wealth of nutritional benefits, including dietary fiber, Vitamin C, and powerful antioxidants like quercetin and anthocyanins. Whether eaten raw for its crisp texture or cooked to bring out its sweetness, red onion adds substantial flavor and a significant nutrient boost to your meals without impacting your daily calorie goals. Adding red onion to salads, salsas, and cooked dishes is a simple and effective way to enhance both the taste and healthiness of your diet.

For more detailed information on a wide range of food and nutrition topics, check out the resources from reputable health and nutrition websites like Healthline.

Frequently Asked Questions

A 50g serving of raw red onion contains approximately 19 to 21 calories, making it a very low-calorie food option.

While cooking a red onion can slightly alter its nutritional composition and bioavailability, the base calorie count will remain low. The calorie content will increase more significantly if oil or butter is used in the cooking process, such as when caramelizing.

Yes, red onions are beneficial for weight management. They are low in calories and fat, but high in fiber, which helps promote a feeling of fullness. This allows you to add flavor to meals without adding a lot of calories.

The primary nutritional benefit of red onions lies in their high content of antioxidants, particularly flavonoids like quercetin and anthocyanins. These compounds are known for their anti-inflammatory and heart-protective properties.

All common onion varieties are low in calories. For a 50g serving, red onions have roughly 19-21 calories, which is very similar to yellow onions. White onions can be slightly lower, but the difference is minimal.

Eating red onion raw preserves heat-sensitive nutrients like Vitamin C, ensuring you get the maximum amount. However, some beneficial compounds like quercetin may become more bioavailable after cooking. A balance of both raw and cooked consumption is ideal.

Red onion is easy to add to meals. You can slice it thinly for salads and sandwiches, dice it for guacamole or salsas, or grill and roast it along with other vegetables.