For what it's worth, Fung considers what you're doing (20:4, 16:8, etc.) to be time-restricted eating (TRE) and recommends that you do this on the days that you don't fast. Nonetheless, I hear lots of people have had success with this to lose weight. If it isn't producing the results you want and you want to go from TRE to intermittent fasting (IF), Janet had some good advice about drinking broth, coffee or tea with cream, etc. to get through those times on actual fast days when you really think you want to eat. After a while you build fasting "muscle" and it becomes easier. The first time I had a full day fast, I think I drank three cups of broth and two cups of tea with cream throughout the day! Along the way, I also had a failed fast, where I ended up eating at 7pm, because I just couldn't stop thinking about food. Yesterday, on just my ninth full-day fast (42-hour), I had a cup of tea with cream as I sat down to watch TV in the evening, and that's it (besides water, of course). It does get easier as time goes on.

I don't think that autophagy reaches its peak rate until sometime after 36 hours, so there are increasing returns to that point, certainly. There's masses we don't know about autophagy, but I see it's potential benefits in fighting cancer, Alzheimer's, excess skin from losing weight, macular degeneration, and many others issues, that I want to try fasting in a way that regularly boosts autophagy. I think at some point I'll try a 72-hour fast to see how it goes, but I think that, for me, beyond that there would probably be a diminishing return regarding enjoyment of life, as you put it.