As with carbohydrates in recent years, fats have been wrongly accused of being "bad." Too much fat can be a bad thing, but certain kinds of fat are actually good for us and are an important part of a healthy diet.
Fats are nutrients in food that the body uses to build nerve tissue (including the brain and nerves) and hormones. The body also uses fat as fuel. If fats eaten aren't burned as energy or used as building blocks, they're stored by the body in fat cells. This is the body's way of thinking ahead: By saving fat for future use, the body plans for times when food might be scarce.