Proteins have 4 calories per gram so if your usual post-workout protein intake would be 20-30g, it'd be 80-120 calories. YMMV but that would move me out of fast. The only calories I ingest during the fast is a little fat for vitamin D bioavailability in the morning.
My caloric window is 1-8pm and I exercise in the mornings with just a few essential amino-acids.
Protein thermic effect is 30% so amount of calories equal to ~30% of that coming from protein is burned to digest protein. You're burning calories, not protein, to digest protein. Those calories are already stored and don't necessarily have to come from protein digestion.
My caloric window is 1-8pm and I exercise in the mornings with just a few essential amino-acids.