Body Fat, layered under the skin and packed around organs, cushions the body against injury, insulates it from cold and supplies calories to meet your energy needs.
The body has a self-protective mechanism that stores fat if continually supplied with more food than is required for your daily energy consumption. To lose part of this fat reserve and stay inside the recommended range of fat in your body, more calories must be burned (used) than you consume in order to force the body to derive the needed energy from the fat reserves.