The physiology of adiposity

Normal energy homeostasis requires a balance between fat storage and energy utilization that is guaranteed by regulation of one billion fat cells which arguably constitute the body's largest endocrine unit. Such physiology is required to maintain normal adiposity which if depleted from under- or malnutrition results in lipodystrophy that causes hormonal, reproductive, and developmental abnormalities. Conversely, excess adiposity provides inflammatory secretagogues, particularly from central visceral fat depots that enhance insulin resistance, excessive fatty acids with lipotoxicity and hypertension that escalate atherosclerosis including coronary artery disease. This review describes normal adiposity for maintenance of normal body mass and the roles of adipocyte hormones and adipokines for normal regulation of energy storage and its utilization. Therefore, in this context, the roles of leptin, insulin, adiponectin, and lesser known acylation-stimulating protein, visfatin, and apelin are outlined. Further, adipocyte inflammatory secretagogues are outlined that affect diabetes mellitus 2 with insulin resistance,fatty acid lipotoxicity, dyslipidemia, and hypertension that contribute to the metabolic syndrome. These effects are opposed by adipocyte hormones adiponectin, acylation-stimulating protein, visfatin, and apelin that help maintain normal energy utilization.