Heat changes the chemical balance of food at the molecular level. Atoms cannot be created or destroyed but can be altered. Heat rearranges how atoms are arranged.
An uncooked fresh apple is still alive, strong with chemical bonds. As soon as you start to cook an apple, you agitate its natural chemical bonds and it forms subpar structures. You will always get more out of foods eaten in their natural state.
Yes, that means meats too. Although not exactly edible in their natural state, the fact still remains you will get better nutrition that way.