Fat cells are not just energy storage vesicles. They are highly active cells that also play a role in the hormonal processes in the body. Not only are they the target of hormones such as insulin and epinephrine, but they also release hormones that play an important role in physiological functions. Hormones such as leptin, irisin, adiponectin, estrogen, resistin, and tumor necrosis factor-a are major players in the physiological processes in the body. This CEC will discuss the hormones and cytokines listed above and what role they play in the body. Also, this CEC will discuss the role of exercise and nutrition in modulating fat cell size and function. While all of these hormones will be covered we will place a particular focus on leptin and its myriad of functions. Attendees will learn about leptin’s effect on the sympathetic nervous system and basal metabolic rate. They will also learn about hyperleptinemia, its causes, and resulting effects.