Age-related weight gain is typically centered around our mid-section; it's abdominal fat (called visceral fat), and it begins to settle in around the time you turn 40 [source: Melone]. It's true that as people age, metabolism slows down and the amount of fat in the body increases, but gaining weight because of those changes isn't inevitable. You do need to kick things up a notch to stave it off, though. The trick? Weights.
Aside from a sensible diet, adding weight training to a cardio-centric exercise routine will help combat age-related loss of muscle mass, called sarcopenia. Combining weight training with cardiovascular exercise also increases bone density, balance and flexibility. And weight training has been found to be better at burning stubborn abdominal fat than aerobic exercise, especially as you age. Plus, the more muscle mass you maintain as the years go by, the lower your chances of dying prematurely [source: Srikanthan].