Exercise and Fat: A Primer.

Over the past 25 years, adipose tissue has emerged as an organ comprising nearly 20 major cell types, including three types of adipocyte subtypes: white, brown, and beige. White adipocytes primarily store energy, brown adipocytes generate heat through thermogenesis and beige adipocytes exhibit intermediate characteristics. Distinct adipose tissue depots vary in their responses to external stimuli such as exercise, partly due to differences in developmental origin and progenitor cell populations. During exercise, adipose tissue contributes to whole-body energy metabolism by releasing lipids, which complement dietary fat intake as a major fuel source. Fat is the predominant substrate during moderate exercise intensities, and beyond its energetic role, lipid metabolism influences metabolic health through diverse signaling functions. Like other organs, white adipose tissue adapts to exercise training by undergoing structural and functional remodeling. Both endurance and resistance exercise stimulate the secretion of hormone-like signaling molecules, termed exerkines, derived from white adipose tissue (adipokines), brown adipose tissue (batokines) and skeletal muscle (myokines). These factors mediate exercise-induced adaptations in white adipose tissue to exercise stimuli and contribute to improvements in metabolic health. This narrative review covers: (1) fat as a chemical molecule in the context of exercise; (2) regulation of fat metabolism during exercise, including the relationship between exercise intensity and substrate oxidation; (3) adipose cell and tissue types; (4) adaptations of white and brown adipose tissue to exercise training; and (5) inter-organ crosstalk involving adipose tissue during exercise.