Metabolic characterization of obesity.

Body composition (adiposity) is a regulated characteristic with multicomponent controls having redundant and interconnecting loops. The nature of the relevant control processes and of their interactions is poorly understood. Components of the system include complex mechanisms controlling food intake; energy expenditure; and the production, location, and filling of adipocytes. Recent studies in humans have implicated three systems in this overall control process: systemic energy homeostasis, adipocyte-related substrate flux, and adrenoreceptor function in adipocytes. These studies indicate that the formerly obese state is characterized by changes in systemic energy expenditure and adipocyte metabolism that may favor regaining weight. The anatomic distribution of adipose tissue, influencing risk of metabolic complications at any absolute level of adiposity, may be partially controlled by the status of adrenergic receptors in the adipocytes of the relevant anatomic sites.