The term "metabolism" refers to the complex set of biochemical processes that take place in the body to convert food into energy. This encompasses both catabolic pathways, which break down food molecules to release energy, and anabolic pathways, which use that energy to build and repair tissues.
Metabolism is fundamental for maintaining the body's energy balance and supporting vital functions such as growth, reproduction, and maintenance of cellular structures. While energy expenditure during exercise, digestion in the stomach, and nutrient absorption in the intestines are all related to how the body processes food, they are specific aspects or related functions, not the overarching definition of metabolism itself. Metabolism includes the entire spectrum of chemical reactions that sustain life, making the definition of metabolism far broader and more encompassing than any single process among the choices.