When John Carter came back from Mars, he recovered his original body, which stayed in the cave while he was over there.
We later learn that while he is on Mars, he left his Earth body in a coma-like state.
Why did his body stay unaltered while he was on Mars? Why didn't he decay or get eaten by insects and/or rodents? If his bodily functions were still active, why did he not run out of nutrients and slim down or dehydrate?