Whether they are cooked or raw, onions are flavorful additions to popular keto dishes, yet you may have been cautioned against the consumption of onions due to their carbohydrate contents. Are onions keto-friendly or not? The consensus seems to be mixed in some nutrition circles, so let’s explore different types of onions to determine if they can fit into your keto nutrition plan.
How Many Carbohydrates in an Onion?
One whole large onion has 14 grams of total carbohydrates so this fact, alone is probably why you have heard some words of caution regarding the onion. A small apple has a comparable amount at 21 grams of carbohydrates, and you are probably aware that apples are not a part of the keto nutrition plan. There is one significant difference between the onion and the apple and that is the way in which we eat them. It is unlikely that you’ll eat a whole onion in one sitting (like you would an apple) so the carbohydrates consumed are drastically reduced.
Onions do have a small amount of fiber so the whole onion contains an average of 11 grams of net carbohydrates.
Let’s move on to more specific varieties of onions so you can choose the best ones for your personal keto macros, and your recipes.
There are only 2.5 grams of net carbohydrates in ¼ of a medium red onion.
Adding ¼ of a medium red onion into your salad, lettuce-wrapped sandwich, or hot dish certainly won’t derail your keto nutrition plan.
Green onions (or scallions) are the most keto-friendly variety of onion. There are only 1.2 grams of net carbohydrates in ¼ cup of chopped green onions.
These make delicious additions to keto-friendly Mexican bowls and chili, or you can add them atop some mashed cauliflower with a dollop of sour cream.
Just like the red onion, you can have yellow onions on keto as well. There are 2.5 grams of net carbohydrates in ¼ of a whole yellow onion.
If you’re making a hot dish that calls for one whole onion, not to worry, that amount reflects a recipe that is (most likely) making four servings.
White onions are low in carbohydrates too—only 2.2 grams of net carbohydrates in ¼ of a whole white onion.
Since it is commonplace to cook some of these varieties of onions, keep in mind that you will need to double your amount of consumed carbohydrates from cooked onions versus raw.
It’s safe to say that realistic serving sizes of onions are suitable for the keto diet. Most recipes don’t call for excessive amounts of onions, but it’s best to double check the serving size just to be safe. Not only are onions keto-friendly, but they also boast impressive nutritional profiles. Compounds in onions have been reported with a range of health benefits, including anticancer properties, antiplatelet activity, antithrombotic activity, anti-asthmatic activity, and antibiotic effects. 
Aimee Aristotelous, author of The 30-Day Keto Plan, Almost Keto, Super Simple Keto, The Whole Food Pregnancy Plan, and The Doctors Weight Loss Diet is a certified nutritionist, specializing in ketogenic and gluten-free nutrition. Her expertise has been featured in Health, People, HuffPost, Parade, Yahoo!, INSIDER, Motherly, Consumer Health Digest, Simply Gluten-Free, Well + Good, and the National Celiac Association. Aimee resides in Fort Lauderdale, Florida, with her husband and son, and enjoys cooking, working out, wine tasting, and traveling.
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