If your end goal is to build more muscle mass, fasting is not the way to go.
But if you want more of a pump or drive in the gym, I would suggest working out after you've eaten.
Or better yet, if your fasting window is large enough, eat something small and easily digested, such as cream of
rice or oatmeal beforehand with a bit of protein, shake some salt on it and enjoy that pump, then finish off with your final
meals after.