When you eat, you begin the process of digestion, which requires your body to expend a lot of time and energy to break down food into molecules that can be absorbed and utilized. Complete digestion usually takes six hours or more. When you eat snacks in between meals, you tax your body. You are asking it to restart a process it has not yet completed from the last time you ate. Not only does this take energy away from other repairs your body is making (hello, tired eyes), but it also leads to weight gain. When your body cannot absorb and utilize food, it stores it as fat. In addition, restarting the process of digestion by snacking cuts short your body’s ability to burn fat in between meals.