A lot of people do this! IMO there are twogood applications for it. 1) when your body is getting used to burning fat for energy, which takes a while (some say 6 weeks or more) 2) when you are relatively lean and your body cannot obtain it’s daily energy from fat stores.
I don’t know if anyone knows the answer about autophagy. All that I’ve read about it say that it occurs in the absence of nutrients and Jason Fung recommends water fasting to insure autophagy. I think the study of autophagy is hot science right now that no one really understands all the mechanisms of.