In theory, when food energy is transferred from one
trophic level to another in a
food chain (from grass to bunny, bunny to hawk, etc.), only about ten percent of the energy is passed on.
So where does it all go? The remaining energy goes into maintaining the organism's internal body temperature, defending against predators, and generally running around being silly. Because so much energy is lost from level to level, from an efficiency point of view it is much better for the state of the world to get our energy straight from plants (or other autotrophs) which produce their own food from solar energy.