Are Onions Keto Friendly? How Many Onions Can You Have?

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From my grandmother, I learned to love the sweet earthy base of slow-simmered onions in butter. But as I started eating low-carb, I needed to know if I would still be able to eat onions on my new ketogenic diet. I did hours of research about the carbs in onions and boiled it down to the essentials to share with you here.

Onions are keto-friendly because we usually eat onions in moderation as a flavor base and not as a major part of most meals. While a whole onion has lots of carbs, a one-half cup serving of sautéed onions has just 2.68 Net Carbs.

Now let’s explore the nutrition profile of onions and how they fit into a Keto Diet.

P.S.  If you are brand new to the keto diet and struggling to figure out what you can and can’t eat, you need to check out my No Cook Keto Meal Plan. It takes all the guesswork out of starting a keto diet and has been used by thousands of people just like you to crush keto.

~ Angela
Picture of two onions
Image of Keto Onions – Photo Credit –

How Many Carbs Are In Onions?

Onions are one of those foods that are a little tricky to track.  This is because, by weight, onions are pretty high in carbohydrates.

For example, a single large onion weighs about 400 grams.  According to the USDA FoodData Central Database, 400 grams of sauteed onions (the equivalent of a large onion) has a hefty 31.44 grams of carbs and only 6.8 grams of dietary fiber!

That means that a large onion has 24.64 grams of Net Carbs! That’s a lot of carbs, but does anyone actually eat that much onion?

You have to keep in mind that a large onion (400 grams by weight) will be around 4.6 cups of diced onions.  That’s a lot of onion for one person to eat in a meal.

It’s more likely that, even if you LOVE onions as I do, you’re not going to be eating more than 1/8 of that, which is about 43.5 grams by weight or about 1/2 cup diced onion, in any single meal.  Honestly, a 1/2 cup of onions is a lot of onions per serving and still will only have 2.68 net carbs.

With those values for carbs in a 1/2 cup serving of onions, choosing to include onions sauteed in butter as a base for your meals seems much more doable while still hitting your carb targets.

Do Any Varieties of Onions have Fewer Carbs?

While there are many varieties of onions including:

  • Sweet Onions
  • Yellow Onions
  • White Onions
  • Spring Onions which are also known as Green Onions or Scallions

Yet with each of these types of onions, the total carbohydrates remain pretty consistent; 3 to 4 grams total carbohydrates per 1/2 cup which is about 87 grams by weight of onion.

What does vary by type of onion is the fiber, and as you know fiber affects net carbs which is what keto diets focus upon.

Here is the fiber content for each of the types of onions we identified above.

  • Sweet Onions = 0.9 Grams Fiber Per 100 Grams by Weight
  • Yellow Onions = 1.48 Grams Fiber Per 100 Grams by Weight
  • White Onions = 1.54 Grams Fiber Per 100 Grams by Weight
  • Spring Onions = 2.6 Grams Fiber Per 100 Grams by Weight

That means that Spring Onions, which are also known as Green Onions or Scallions, are the most keto-friendly onions, though any type will fit most keto diets in normal moderation as a flavor base for cooked meals.

Perhaps as importantly, these spring onions have the same general health benefits of other types of onions, but we’ll go into those benefits a bit later.

Please note that while shallots look similar to onions, nutritionally they are much different. Specifically, shallots have nearly two times the carbohydrates of most varieties of onion and only about 1/2 of the fiber. Avoid shallots on a Ketogenic Diet!

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Health Benefits of Onions on A Keto Diet?

Onions are very nutrient-dense, which means that they are high in nutrition while being low in calories. Now on a Keto Diet, we’re not as worried about calories as we are carbohydrates, but it’s fair to say that onions are also nutrient-dense in comparison to their carb content.

Particularly, according to the USDA FoodData Central Database, they are high in Vitamine C and Potassium. Potassium is particularly intriguing, as it’s a nutrient that is hard for many people to get in a normal Standard American Diet (SAD).

There are also studies that suggest that onions contain antioxidants and other compounds that might help prevent cancer. Honestly, I have no idea if any of that is true, but in time research will give us a final answer.

In the meantime, I don’t find any research that suggests that onions cause harm in any way unless you eat so many that the carbohydrates overload your ketosis.

Conclusion on Onions On A Ketogenic Diet

Most recipes call for just a tablespoon or soon of onions, and at that amount, onions add a ton of flavor and very few carbs.

As long as you’re not eating onions like you’d eat an apple, then enjoy their sweet and savory goodness as a base for all of your recipes!


P.S. If you want more “Is It Keto” articles like this one, I’ve created a list of these articles. Just Click Here. ~Angela

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Angela Davis

I'm Angela Davis, Co-Founder of Advantage Meals. I have a Bachelors in Anthropology and Masters in Holistic Nutrition. My passion is Ancestral Nutrition and for over a decade I've been helping Keto Diet beginners and those looking for their Primal Diet. "There is no one right way." Below are the most recent articles I've written for

2 thoughts on “Are Onions Keto Friendly? How Many Onions Can You Have?

  1. I am eating a steak i just cooked in fry pan w a whole chopped up med onion and I’m eating it all. I had 8 carbs for breakfast. So i better watch out! Btw I’m down 31 lbs n super up in energy! Tks keto!

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