How many calories are in 40 grams of white onions?

November 19, 2025 •

4 min read

According to reputable nutrient databases, a 40-gram serving of white onion contains approximately 16 to 17 calories. This makes the white onion an excellent, low-calorie ingredient for adding flavor to countless dishes and a perfect addition to any diet focused on calorie management.

Quick Summary

A 40-gram serving of raw white onion contains about 16-17 calories and is rich in nutrients. It's a low-calorie ingredient that adds flavor while providing fiber, antioxidants, and vitamins.

Key Points

Low Calorie Count: A 40g serving of white onion contains only 16-17 calories, making it ideal for low-calorie diets.
Rich in Nutrients: White onions are packed with vitamins (C, B6), minerals, and antioxidants like quercetin, supporting overall health.
Supports Gut Health: The prebiotic fiber in onions, known as fructans, nourishes beneficial gut bacteria and promotes healthy digestion.
Minimal Impact of Cooking: The calorie count of onions remains low when cooked, provided you don't add large amounts of high-fat ingredients like oil or butter.
Versatile Flavor Enhancer: Due to their low-calorie profile, white onions can be used liberally to add flavor to numerous dishes, from salads to stir-fries, without guilt.
Comparable to Other Varieties: The caloric difference per gram between white, yellow, and red onions is minor, so flavor preference is the main deciding factor.

Calorie Breakdown: How many calories are in 40 grams of white onions?

For anyone tracking their calorie intake, understanding the precise energy content of food is crucial. A 40-gram portion of raw, chopped white onion is remarkably low in calories. Based on data from sources like Healthline and nutrient calculators, the amount typically falls between 16 and 17 calories. This minimal calorie count is one of the reasons onions are a versatile and popular ingredient in healthy cooking. A 40-gram serving is a standard amount often used to add aromatic flavor to a dish, which means you can significantly enhance your meals without adding substantial calories.

Macronutrient Profile for a 40g Serving

Beyond the raw calorie count, the macronutrient breakdown reveals why onions are such a nutritious choice. The calories primarily come from carbohydrates, with trace amounts of protein and fat. For a 40-gram portion of white onion, the approximate nutritional composition is as follows:

Carbohydrates: Approximately 4 grams. Most of the carbohydrates are composed of simple sugars and fiber.
Protein: About 0.4 grams.
Fat: Less than 0.1 grams.
Fiber: Around 1 gram, which is beneficial for digestion.

This breakdown demonstrates that white onions are an excellent source of flavor and fiber for very few calories, making them a great choice for bulking up meals while keeping calorie density low.

Beyond the Calories: Health Benefits of White Onions

White onions offer more than just low calories; they are packed with health-promoting compounds. They contain a variety of vitamins, minerals, and antioxidants that contribute to overall wellness. Some key health benefits include:

Rich in Antioxidants: Onions are a top source of flavonoids, particularly quercetin, a potent antioxidant that may help reduce inflammation and blood pressure.
Support for Gut Health: White onions are rich in fructans, a type of soluble fiber that acts as a prebiotic. These prebiotics feed the beneficial bacteria in your gut, supporting a healthy digestive system and potentially reducing inflammation.
Nutrient-Dense: They provide a good source of Vitamin C and Vitamin B6, which are essential for immune function, collagen production, and metabolism.
Support Heart Health: The organosulfur compounds in onions have been linked to helping lower blood pressure and cholesterol levels.

The Effect of Cooking on Onion Calories

Cooking methods can alter the calorie content of onions, but not significantly unless additional ingredients are used. A raw white onion and a boiled white onion will have virtually the same low calorie count. However, if you add oil or butter to sauté or caramelize onions, you will dramatically increase the calorie total. For example, sautéing a 40-gram portion in a tablespoon of oil (approx. 120 calories) would bring the total to about 136-137 calories. For a low-calorie diet, it is best to cook onions by sautéing in a non-stick pan with a small amount of cooking spray or water, or by roasting them without excessive oil.

White vs. Other Onion Varieties: A Caloric Comparison

While the focus is on white onions, it is helpful to see how they stack up against other common types. The caloric difference between varieties is minimal, so your choice is more likely to be based on flavor profile than on calorie content. The following table compares the calorie count and macronutrients for 100 grams of raw, chopped onion based on published data.


Nutrient (per 100g)	White Onions	Yellow Onions	Red Onions
Calories	36	38	44
Carbohydrates	7.68g	8.61g	9.93g
Fiber	1.2g	2.71g	N/A
Fat	0.13g	0.05g	0.1g

Note: Fiber data for red onions is not consistent across all sources, but is generally comparable.

Easy Ways to Add Onions to Your Diet

Given their low-calorie and high-flavor profile, incorporating white onions into your daily meals is simple and delicious. Here are a few easy ideas:

Salads: Finely slice or dice raw white onions for a crisp, pungent addition to any salad.
Salsas and Dips: The sharp, clean flavor is perfect for homemade salsas, guacamole, and other dips.
Roasted Vegetables: Chop them into wedges and roast with other vegetables for a savory side dish.
Soups and Stews: Sautéing onions as a base for soups and stews is a classic way to build a complex, flavorful foundation.
Stir-fries: Add chopped white onions to stir-fries for added texture and a delicious aromatic flavor.
Sandwiches and Wraps: A thin slice of raw onion can provide a burst of flavor to sandwiches, wraps, and burgers without significant calories.

Conclusion: White Onions as a Low-Calorie, Flavorful Addition

In summary, the number of calories in 40 grams of white onions is a very low 16 to 17, making them an excellent choice for a health-conscious diet. They are a nutritionally dense vegetable, offering valuable vitamins, minerals, and antioxidants for minimal caloric cost. The slight caloric variation between white, yellow, and red onions is negligible, so you can choose based on your preferred taste. Incorporating this versatile vegetable into your cooking is a simple and effective way to enhance flavor and boost your nutritional intake without compromising your calorie goals. For more detailed nutritional information, check out reputable databases such as Healthline.

Frequently Asked Questions

A 40-gram serving of raw white onion contains approximately 16 to 17 calories.

Cooking white onions by themselves (boiling, steaming) does not significantly increase their calories. However, adding fats like oil or butter for sautéing or caramelizing will increase the total calorie count of the dish.

All onion varieties are healthy and low in calories. While they have slightly different flavor profiles and nutrient compositions, the calorie difference per gram is minimal and not a major factor in overall health benefits.

A 40-gram portion is roughly equivalent to about a third of a medium-sized onion or a few generous tablespoons of chopped onion.

Yes, white onions are suitable for many low-carb diets. A 40-gram serving contains about 4 grams of carbohydrates, which can be easily incorporated into a balanced eating plan.

White onions are a good source of fiber, antioxidants (like quercetin), and vitamins, supporting digestion, reducing inflammation, and promoting heart health.

To add flavor without extra calories, you can use white onions raw in salads, roast them with a light spray of cooking oil, or sauté them in a pan with a splash of water or broth instead of oil.