I’ve not found anything that indicates it’s not healthy when done within reason. That is you remain hydrated and have the fat reserve to burn. So fasting doesn’t exclude water. Tea and coffee would be permitted as well as long as no sugar or milk. I also understand the intermittent fasting typically maxes around 72hrs.

Anecdotally, I found it highly effective as part of my dieting routine. I only did the intermittent fasting as a period of “you’re not supposed to eat between these times.” Now if I felt I wanted to break the fast, I made myself spend the effort and make something healthy. I let myself eat if I was actually hungry, but it had to be a real good-for-me meal and something that required dedicated time to make if breaking the fast.

My fasting target was from 8:30pm to 12:00pm the next day. The pattern and habit seems to help control that “boredom hunger”.

I found tracking everything I ate and using a food scale helped me learn what a serving size really is.

I see a lot of keto/low carb hate, but it’s the only one that worked for me. I was able to lose weight and not be hungry all the time.