It's common for people to pack on more pounds as they age, but now a new study may have an explanation for this weight gain — and it has nothing to do with exercise or poor food choices. Researchers identified an enzyme that appears to increase its activity in animals as they age. The increase in this enzyme's activity may play a role in the weight gain and fitness decline that come with aging, they said. In experiments in mice on a high-fat diet, the researchers found that mice that had this enzyme blocked gained less weight than normal mice. Our society attributes the weight gain and lack of exercise at mid-life … primarily to poor lifestyle choices and lack of will power," study author Dr. Jay Chung, head of the Laboratory of Obesity and Aging Research at the National Heart, Lung, and Blood Institute, said in a statement. "But this study shows that there is a genetic program driven by an overactive enzyme that promotes weight gain and loss of exercise capacity at mid-life," Chung said. [The Best Way to Keep Weight Off]

Because the new study was conducted in mice, researchers don't yet know if blocking this enzyme in humans will have the same effect. But the researchers said that, with more research, the findings could potentially lead to the development of new weight loss medications that would block this enzyme.

 Read more from the Journal Cell Metabolism.