What is the process through which the body obtains and utilizes energy from food?

Metabolism refers to the comprehensive set of biochemical reactions that occur within the body to convert food into energy. This process encompasses both catabolism, where larger molecules like carbohydrates, proteins, and fats are broken down into smaller units, releasing energy, and anabolism, where the body uses that energy to build and repair tissues.

Metabolism is crucial because it not only involves energy production but also determines how the body uses food for various functions, including growth, maintenance, and repair. It plays a significant role in maintaining homeostasis, regulating how nutrients are processed and utilized based on individual energy needs.

Digestion, while an essential component of nutrient intake, primarily refers to the mechanical and chemical breakdown of food in the gastrointestinal tract. Absorption is the subsequent step where the nutrients are taken up by the cells after digestion. Circulation pertains to the movement of blood and other bodily fluids throughout the body, delivering nutrients and oxygen to cells but does not specifically relate to the utilization of energy from food itself. Thus, metabolism encompasses the entire process of energy conversion from nutrients, making it the correct choice.