Energy, in the context of nutrition, refers to the amount of usable fuel (calories) provided by consuming food and beverages. With energy, our bodies have the foundational support to run all the biological processes necessary to sustain life. Last Updated:March 26, 2025 In the nutrition context, “energy” is most commonly used to describe calories. The two terms are used interchangeably, but calories are a defined unit that measures the body’s use of energy..