This all falls under intermittant fasting.
IIRC, this is the PMenu party line on it: I could have some details wrong.
Concern: Maximal Fat loss
Train in fasted state. Remain in fasted state for a few hours after training.
Concern: Muscle retention/fat loss
Train in fasted state. Utilize an intelligent "paleo" post workout meal
Concern: Muscle retention&gain/slower fat loss
Break fast prior to training, ~1 hour, with small protein meal (some carbs ok, some fat ok). Post-workout insulin spike with protein and carbs.