It doesn't take much time sitting around to slow down the process by which your body converts food into energy and regulates multiple biological processes. In the time it takes to watch just one episode of "Game of Thrones" (about an hour of sitting), your body slows down its production of the fat-burning enzyme lipase by 90 percent. When your metabolism slows down, if you don't also slow down your caloric intake and up your exercise you're going to gain weight. But you also lose, too -- your body loses the good cholesterol, HDL, that keeps the bad LDL cholesterol in check, putting you on a path toward cardiovascular disease. You'll also lose efficiency in how well your body is able to effectively manage insulin, steering you toward diabetes.