<prompt> Fatty acids are the main source of energy forMusclesHeartLiverRBC  <response>: Fed state Preferred fuelStarvation preferred fuelRBCGlucoseGlucoseHeartFatty acidsKetone bodiesBrainGlucoseKetone bodiesLiverGlucoseFatty acids proteinMuscleGlucoseFatty acidsAdipose tissueGlucose Fatty acids. 