An enzyme is a protein that carries out the biochemical reactions essential for the body to metabolize food and produce energy for growth, repair, and movement.  They are needed to help break down foods for absorption and utilization.

Enzymes are found throughout nature.  Enzymes are found in animals as well as in foods.  Organisms could not function if they had no enzymes.

The defining characteristic of an enzyme is that it changes things around it without changing itself.