As the game advances, you will get starving. You will require to eat to sustain your health bar to 100%, in addition to sleep. You can quickly head on to them with a knife and kill them when you see bunnies and chickens. They will drop some food that you can then eat once they are dead. If you keep on consuming while you are currently full, you will start throwing up, so attempt not to do that as much as possible. The health bar can be brought back by sleeping, however I recommend sleeping on a bed rather of a flooring, since that will not reduce the energy levels.