How Many Carbs Are in a Raw Onion?

November 11, 2025 •

4 min read

Raw onions are a versatile and nutrient-dense ingredient, prized for their ability to add flavor without excess calories. A typical 3.5-ounce (100-gram) serving contains roughly 9.3 grams of total carbohydrates. This guide details exactly how many carbs are in a raw onion and provides a breakdown by variety to help you manage your intake effectively.

Quick Summary

This nutritional guide breaks down the carbohydrate content of different raw onion varieties, including total and net carbs. It explains how to manage portion sizes for low-carb diets like keto and discusses additional health benefits beyond flavor, such as prebiotic fiber and antioxidants. The guide also compares carb counts across common types and offers advice for minimizing intake while cooking.

Key Points

Moderate carb content: A 100g serving of raw onion contains about 7.6 grams of net carbs.
Variety matters: Green onions have significantly fewer carbs (3.9g net per 100g) than red onions (7.7g net per 100g).
Flavor concentration: Due to their strong flavor, a small amount of onion is often sufficient, keeping the carb count low.
Rich in nutrients: Raw onions offer valuable prebiotics, antioxidants (especially quercetin), and sulfur compounds.
Manage with cooking: Caramelizing onions increases their sugar and carb density, so using raw or minimally cooked onion is better for low-carb diets.

What are the carbohydrates in a raw onion?

Raw onions contain carbohydrates, with the exact amount varying slightly depending on the variety and serving size. For a standard reference, a 3.5-ounce (100-gram) portion of raw onion provides approximately 9.3 grams of total carbs and 7.6 grams of net carbs. Net carbs are calculated by subtracting the fiber content from the total carbs, representing the carbohydrates that the body digests and uses for energy. Raw onions are notable for containing fructans, a type of prebiotic fiber that feeds beneficial gut bacteria but may cause digestive issues for individuals sensitive to FODMAPs.

Carb content breakdown by onion type

Not all onions are created equal when it comes to carbohydrate concentration. Those on a strict low-carb or ketogenic diet should be mindful of the differences, as some varieties are more carb-dense than others. Green onions, or scallions, stand out as the most keto-friendly option due to their low net carb count.

Carbohydrate Comparison per 100g (raw)


Onion Variety	Total Carbs (g)	Dietary Fiber (g)	Net Carbs (g)
Green Onion	5.7	1.8	3.9
White Onion	7.7	1.2	6.5
Yellow Onion	8.6	1.9	6.7
Sweet Onion	7.5	0.9	6.6
Red Onion	9.9	2.2	7.7

As the table illustrates, there are noticeable differences, with green onions offering the lowest net carb count, while red onions have the highest. For those counting every carb, selecting green or white onions is the most effective strategy.

Health benefits of eating raw onions

Beyond their flavor, raw onions are packed with nutrients and compounds that provide a range of health benefits.

Antioxidant powerhouse: Raw onions are rich in antioxidants, including quercetin, which helps protect the body's cells from damage caused by free radicals. This anti-inflammatory effect is particularly high in the colorful varieties like red and yellow onions, with cooking potentially reducing some compounds.
Promotes digestive health: The prebiotic fibers found in onions, particularly fructans and fructooligosaccharides, feed the healthy bacteria in your gut. These fibers bypass digestion and reach the large intestine, where they are fermented by gut microbes, producing beneficial short-chain fatty acids (SCFAs) that support gut health.
Supports blood sugar control: Studies suggest that consuming raw onions may help regulate blood sugar levels. The sulfur compounds and quercetin in onions may aid in boosting insulin production and sensitivity, which is beneficial for managing diabetes.
Contains antibacterial properties: The sulfur compounds in onions, such as thiosulfinates, possess natural antibacterial properties that can help inhibit the growth of harmful microorganisms.
Enhances heart health: The organic sulfur compounds in onions can help reduce cholesterol and triglyceride levels, and may help break down blood clots, lowering the risk of heart disease.

Practical tips for low-carb diets

Integrating raw onions into a low-carb diet requires portion control to avoid exceeding your daily carb limit. Because onions are potent in flavor, a little goes a long way. Use them as a garnish rather than a main vegetable. For instance, sprinkling a small amount of finely diced red onion on a salad or using green onions as a garnish can add a burst of flavor with minimal carb impact.

How cooking affects carb count

Cooking onions, particularly through caramelization, can concentrate the sugars, slightly increasing their carbohydrate density. While raw onions are generally the best option for maintaining a low carb count, some cooked methods can still be part of a low-carb plan when portions are controlled. Sautéing or grilling in a low-carb fat source like butter or olive oil is a preferable method over deep frying. To reduce some of the sharp flavor of raw onions, you can soak the chopped pieces in cold water for 30 minutes before adding them to your dish.

Conclusion

Raw onions are a flavorful and nutritious vegetable that can be a healthy part of almost any diet, including low-carb and ketogenic lifestyles, as long as they are consumed in moderation. With approximately 7.6 grams of net carbs per 100 grams, they are not a carb-free food, but their potent flavor means a small portion can add a lot of impact. Choosing lower-carb varieties like green or white onions and controlling your serving size are key strategies for managing carb intake. Furthermore, the robust health benefits, including antioxidant and prebiotic properties, make raw onions a beneficial addition to your diet. For specific guidance, you can explore the USDA FoodData Central database to review detailed nutritional information for various foods.

List of low-carb onion uses:

Add finely chopped red onion to salads.
Sprinkle green onions on soups, chilis, and stews.
Use white onion in salsas and dips.
Garnish with thinly sliced onions for a fresh bite.
Sauté small amounts with other low-carb vegetables like mushrooms and bell peppers.

In summary, knowing the carb counts of different onion varieties empowers you to make informed dietary choices and enjoy the flavor and health benefits of raw onions without compromising your nutritional goals.

Frequently Asked Questions

Onions have a moderate carbohydrate content compared to other vegetables. While not as low as leafy greens, they can be included in a keto diet when used in moderation, as a flavor enhancer, to stay within your daily carb limit.

Green onions, also known as scallions, contain the fewest carbs per serving, making them the most keto-friendly onion variety. A 100g serving has only 3.9g of net carbs.

To enjoy onions on a low-carb diet, use them sparingly. Incorporate small, finely diced portions into salads, salsas, or as a garnish for meals. This adds flavor without a significant carb load.

Yes, cooking can affect the carb concentration. Caramelizing onions, for example, concentrates their natural sugars, slightly increasing the carbohydrate density. For the lowest carb impact, consume onions raw or lightly sautéed.

Net carbs are the total carbohydrates minus the dietary fiber. For raw onions, this calculation is relevant for those following low-carb diets, as the fiber is not digested by the body. A 100g serving of raw onion has around 7.6g of net carbs.

Yes, you can have raw onion on the keto diet. Since it adds significant flavor in small quantities, you can use it to enhance your meals while keeping a close eye on your portion size to manage your daily carb intake.

Yes, there is a slight difference. Red onions typically have a higher carb count than white onions. Per 100g, red onions contain approximately 7.7g net carbs, while white onions have about 6.5g net carbs.