Comparative anatomy and metabolic profiles of brown and white adipose tissue in humans

Adipose tissue is a dynamic metabolic organ that plays a central role in energy homeostasis, endocrine signaling, and thermoregulation (Forner et al., 2009). Traditionally, adipose tissue has been classified into two major types: white adipose tissue (WAT), which primarily stores energy as triglycerides, and brown adipose tissue (BAT), which dissipates energy as heat through non-shivering thermogenesis. While WAT is widely distributed throughout the human body, BAT is more abundant in small mammals and infants but remains present and metabolically active in specific regions of adult humans. Recent molecular biology discoveries and imaging methods have reshaped the physiological status of BAT and recognized the presence of beige or brite adipocytes, which develop in WAT depots and display thermogenic potential. This led to renewed attention on adipose tissue plasticity and how it is relevant for metabolic health, obesity, and associated metabolic disorders. This narrative review compares the anatomical distribution, cellular morphology, developmental origins, and physiological functions of WAT and BAT in humans. It also summarizes imaging modalities used to identify metabolically active adipose tissue and discusses emerging concepts such as adipose browning, endocrine signaling, and therapeutic activation of thermogenic fat.