I do a 16/8 plan most of the time and this week I've started having 2 fast days a week too. I was going to eat the 500 or so calories but I was not hungry at all so just had some cofee with heavy cream and felt fine.
I didn't find ant difference in my workout but I'm not doing heavy weights or anything, just bodyweight.
Must say I felt great the following morning. Clear headed and energetic as always!