I have tried 24hr fasting periods and didn’t like them. However, I have had a lot of success with IF. Specifically, using the Leangains method that was developed by Martin Berkhan (16hr fast/8hr feed). He has a LOT of compelling information on his site (taken from peer-reviewed literature).
I have used this method to “cut”, as well as to gain muscle. The key is caloric/macronutrient manipulation. I like eating this way, I function well with this method, and, shockingly, I am never hungry. I find this very sustainable (for ME, anyway).
I tend to not recommend this to clients (unless they REALLY want to know what it is about) for a few reasons.
1. This still requires you to count calories. I find that people without experience who use this method can find themselves severely under-eating.
2. On the flip side of the coin, some people will complete their daily fast and use that as an excuse to completely binge eat. Not cool.
3. In order meet caloric requirements, you need to eat BIG. Some people simply cannot get used to eating a lot of food. (It is not uncommon for me to eat 4 chicken breasts in one sitting on off-days.)
That being said, I think this is a powerful tool when used correctly. Trust me, no one was more skeptical than I was until I tried it.
A lot of the fasting controversy comes from individuals who seem to think that metabolism is a function of meal frequency, which is not the case. I would definitely get into the literature, as there is some surprising information, if you look.