It was pointed out in the series that Clark really didn't need to eat, but he enjoyed doing so. He derrived most if not all of his energy from sunlight. However in this alternate universe he is lacking the ability to convert sunlight to energy. It is also pointed out at some point that he does expend a lot of energy. Logically if his primary source of energy is made ineffective it needs to be replaced by something and that something needs to meet the higher output requirements attendant to the higher metabolic rate.
