I am doing IF about 3-4 times per week. Your body does get used to it.
IF and Keto diets are related. This is worth noting.
Dr. Jason Fung whose written 2 books.
https://www.youtube.com/watch?v=v9Aw0P7GjHE
https://www.youtube.com/watch?v=vSttZ6EmcWs
https://www.youtube.com/watch?v=GbqCPhSMsU0
I've watched a lot of health / Keto videos blogs and this guy is one of the best, if not the best I've seen: Bob Briggs.
https://www.youtube.com/watch?v=7sAqy1lnWXo