Dr. Fung has some data showing HGH levels peak at 18 hours into a fast. HGH will help you retain or grow some muscle while you’re following a fasting protocol.
Coach Greg is right, you’re gonna be missing out on maximizing your muscle protein synthesis. You’ll still gain so long as your protein and training are right, but it’ll be slower than someone not fasting. Islosing some weight worth slowing down your muscle gains? That’s the question you have to answer.
From my experience, building muscle through weigtlifting can decrease fat and increase muscle. Your clothes will fit differently but you may actually gain weight as you increase muscle mass. My experience is based on increased calorie intake without IM.