are onions keto?

In a comment, my buddy Charles remarked on a bit of internet research he'd done, during which he stumbled upon the idea that onions aren't keto. I hadn't actually thought about this before, and truth be told, I'd simply assumed that onions were completely keto-friendly. As it turns out, though, your typical white onion has about 6% carbs by weight, making it rather sugary, and so there are indeed keto folks who reject the use of onion in keto food (green onions are a common replacement). 

However, a bit of further research turns up the idea that—as with tomatoes, which are also sugary—onions can be used by keto-heads, but in moderation. As I remarked to Charles, I've seen plenty of keto recipes that incorporate onions, which merely fueled my admittedly uncritical assumption that onions were perfectly okay on keto. So I guess the answer to the question of whether onions are keto-friendly is yes and no. Onions are sugary, but much depends on how they're used in a dish, and to what degree the dish is divided up.

While many keto dieters try to avoid white or red onions because of their higher sugar content (6 grams per 100 grams), ...scallions are actually a great onion substitute, as they contain half the sugar amount of onions, but still have a ton of health benefits (think fiber and beneficial sulfur compounds). (source)  

Onions And Keto CAN Go Together (source)  

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 [grams of] net carbs. (source)

This works for me: I'm no lover of onions in large quantities, but relegating onions to a background flavor suits me just fine. I often use dried-onion flakes instead of real onions in dishes that require onions, and I'm also okay with puréed onions. I don't think I hate the taste or smell of onions as much as I do the feel of them. There's just something stringy, fibrous, and overall vomitous about large chunks and long strands of onions. Keep the taste; ditch the texture. Do that, and I'm a happy camper.