The understanding of the twin epidemics of obesity and diabetes is changing. The "calories in, calories out" model is giving way, faster and faster, to a more nuanced view. The brain, molecular medicine, hormonal differences, and genetics are all coming into play as we consider this new paradigm. Drs. Dale Abel and Miguel Lopez are two researchers--one in Iowa, one in Spain--working to advance the science of these world-wide epidemics, and Taz Khalid, Aline Sandouk, and Eric Wilson want to know: where is this train headed?