Carbs in Onions

Carbohydrate Info, Calories, Fiber, Health Benefits, and Recipes

Close up of chef chopping vegetables
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Onions are prized in cooking all over the world for the flavors they impart to almost any dish. Did you know that the reason they irritate the eyes is due to a mild sulfuric acid which is produced and released when chopping them? Some remedies to try (in declining order of effectiveness, but all have been shown to be of some help): wearing goggles, chilling the onion before slicing, breathing through your mouth when slicing, and lighting candles around the cutting board.

Carbohydrate and Fiber Counts for Onions

  • ½ cup of chopped raw onion: 6 grams of effective (net) carbohydrate plus 1 gram of fiber and 32 calories
  • 1 medium onion (2.5" in diameter; about 4 oz.): 8 grams of effective (net) carbohydrate plus 2 grams of fiber and 44 calories
  • 1 slice of raw onion, 1/8 inch thick: 1 gram of effective (net) carbohydrate and 6 calories

Looking for a lower-carb substitute for onions? Try green onions (scallions, spring onions).

Glycemic Index for Onions

As with most non-starchy vegetables, there is no scientific study of the glycemic index of onions. However, some of the carbohydrates in onions is in the form of oligosaccharides, which would tend to lower the glycemic effect.

More Information about the Glycemic Index

Estimated Glycemic Load of Onions

  • ½ cup of raw chopped onions: 2
  • 1 medium onion (2.5" in diameter; about 4 oz.): 4
  • 1 slice of raw onion, 1/8 inch thick: 0

More Information about the Glycemic Load

Health Benefits of Onions

Onions are a good source vitamin C and a very good source of chromium. They are also high in quercetin, and as mentioned above, oligosaccharides.  They also contain many phytonutrients, such as polyphenols, flavonoids, and sulfur-containing compounds which are being shown to have healthful properties.

  Red onions have more of some of these substances than yellow onions, and white onions have the least, but still contain many phytonutrients.

Onions have been thought to have many different types of health benefits. There are hints in animal and some human studies that they are heart-healthy and may have anti-diabetic properties, as well as promoting anti-inflammatory and anti-bacterial activity in the body. The evidence is stronger that onions have an anti-cancer effect, particularly in regards to gastrointestinal cancers, including colon and stomach cancers.

Low-Carb Recipes with Onions

I would venture to say that most of my low-carb main dishes have at least a little onion in them. Here's a sampling of some of my recipes which include onion:

More Carb Profiles:


Galeone C, Pelucchi C, Levi F, Negri E, Franceschi S, Talamini R, Giacosa A, La Vecchia C. Onion and garlic use and human cancer. Am J Clin Nutr. 2006 Nov;84(5):1027-32.

Leroux, MarcusFoster-Powell, Kaye, Holt, Susanna and Brand-Miller, Janette. "International table of glycemic index and glycemic load values: 2002." American Journal of Clinical Nutrition. Vol. 76, No. 1, 5-56, (2002).

USDA National Nutrient Database for Standard Reference, Release 28.

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