Digestion is the process by which the body obtains nutrients from the environment, notes Wikipedia. Without these nutrients, a living body would gradually run out of the energy necessary to maintain health. Eventually, a body that can no longer digest food starves to death.
The laws of thermodynamics dictate that energy cannot be created from nothing, according to Memorial Hermann. This means that any energy a living body uses must come from an external source. For most animals, this means consuming organic matter and breaking it down into useful compounds. Digestion is the process by which humans, and many other animal species, accomplish this intake of energy, states Wikipedia.