Our body needs energy to actually perform any action. We get most of our energy from eating and drinking. If we don’t have energy, our everyday processes can’t actually happen. I haven’t taken biology since middle school, so I can’t provide a better explanation that that. Also, when you starve, your body starts eating itself and using fat as energy. This creates ketones and could cause multiple other health problems like a coma. You’ll most likely die. And, your immune system will most likely shut down and you’ll get sick 10x easier