I'm pleased to find this thread here! I've been researching fasting for quite a while now. I have no personal experience on extended ketogenic eating, but quite a lot of experience on sporadically fasting and conversing with a lot of keto and fasting users. My normal fasting is a strict fast, zero calories, only water. I do not do it at regular intervals though, because I find the more flexible I can be with it, the better it works for me and the more sustainable it is. I've seen people mean a lot of things by intermittent fasting. Some consider a restricted eating window, like 16:8 or 20:4, to be intermittent fasting. You're technically fasting during the lion's share of the day but I think it's better to just call it a restricted eating window, rather than fasting. Because it can still feel quite normal, and satiating, and can be done indefinitely, maintaining your normal weight. I don't even like to call it a diet. It's just a way of timing what you choose to eat. A lot of people simply eat what they'd normally want to eat within that time frame, no bother in calorie counting, and no bother as to ratios of macronutrients, etc, and still see beneficial results from it, I've noticed. It helps to know who is defining the term and how.
Then there's the idea of a fasting mimetic way of eating and an alternate-day fasting that has research out there. Although the "fasting" might be something of a misnomer, again, and it matters who is defining it. If you treat the meaning strictly as only water, the way I usually mean it, a lot of these really aren't that strict. Many alternate-day fasts, are just cycling on and off between very low calorie and regular calorie days. It might also be far easier than fasting the way I do it. It can still be very beneficial, but it's not going "all in."
Ketogenic diets and intermittent fasting can be combined as well, so it doesn't have to be mutually exclusive. If you're fasting through most of the day, then eating a ketogenic meal, like a steak and an avocado, you've combined the ideas, essentially, and if you feel well doing it, it might be a powerful route for you.
If you're interested in any of those meanings of fasting, I can direct you to some videos with some of the doctors who research and employ the protocols, giving explanations about the kind of interesting processes the body goes through when forced to adapt during fasting, and some of the background on animal studies, as well as some patients showing you how they incorporate it into their lives, in documentaries and interviews. You may have already found them though by now. As a side note, I think we're going to see more and more about these types of diets with regard to disease treatment and prevention of the big three (diabetes, cancer, heart disease). Anyway, another note on Keto VS IF is that extended fasts will necessarily put you in ketosis anyway, if you choose to extend them to that point, which you certainly don't have to do, in order to practice fasting. Still worth noting.
Look for something more sustainable, imo. Both of those diets are based mostly in pseudoscience/bro science.
I have not found that to be true at all in my research on it, Blues. But neither ketogenic nor intermittent fasting really addresses a specific diet, by definition. Because you can come up with all kinds of strange eating habits within those two ways of eating, and they may be healthy or not, and the science may promote or discourage them, is the problem I have with this framing. Once you get into the matter, you realize each label can be very vague to practitioners. Too vague. There is plenty of very real science by very real scientists to base these practices on. But you can have a ketogenic diet of nothing but Bob Evans sausages, and someone try to justify it with real science, wrongfully. It doesn't mean the scientists involved in the real research are telling people to do that, that I know of. You can fast 24 hours on, 24 hours off and break each fast with a bucket of chocolate ice cream, in its entirety, but it's not like anyone from the NIH who advocates for fasting is recommending that. Yet, you can do those things based on the vague terminology.
That is why, like the term "supplements," it is too vague to defend against charlatans latching on and going for a ride with it, but it does not discredit the concepts as useful or the science they're based on. Maybe you've seen a lot of bro science pundits advocating for these practices, or using unscientific explanation or justification, but there is a large fasting community and keto community I have seen simply basing their diets on MD's, biologists, etc, having put the ideas to the test in the domain of legitimate science.