The current obesity epidemic has focused a great deal of attention on mechanisms controlling energy balance. While diet and nutrient absorption affect energy intake, on the other side of the equation, energy expenditure is determined by basal metabolism, physical activity, and adaptive thermogenesis. Given various challenges in modulating these energy balance mechanisms to combat human obesity, many efforts have concentrated on how it might be possible to achieve weight loss through increased thermogenesis. In this issue of Cell, Kazak et al. describe a previously unrecognized molecular pathway for thermogenesis in fat cells.
