Researchers have uncovered a destructive mechanism at the molecular level that causes a well-known phenomenon associated with obesity: leptin resistance. They found that mice fed a high-fat diet produce an enzyme named MMP-2 that clips receptors for the hormone leptin from the surface of neuronal cells in the hypothalamus. This blocks leptin from binding to its receptors. This in turn keeps the neurons from signaling that your stomach is full and you should stop eating.