Perhaps leptin and its involvement in many areas of reproductive physiology may be of greatest interest outside of obesity, but other physiological arenas are becoming increasingly involved in the broader understanding of leptin and its pleiotropic functions. Leptin, of course, remains of great interest in obesity and diabetes but other, previously unimagined, areas are now in the realm of leptin physiology. Today leptin, with almost 11,000 reports in the world's literature, is recognized to be important in many areas of physiology with strong suggestions for involvement in clinical conditions as well. Early studies actively investigated many aspects of metabolism, obesity, and diabetes but it was soon evident that leptin was much more than a metabolic hormone. The discovery of leptin by Friedman and his colleagues in 1994 was a seminal discovery in the study of metabolism, providing a new tool to study energy expenditure and appetite regulation.
