If burning fat is one of your goals for working out, you may want to skip your post-workout snack.  Reporting in the Journal of Applied Physiology, Nutrition, and Metabolism (2007), investigators found that after a 1-hour walk on the treadmill, study subjects experienced a 40% boost in insulin efficiency (which translates to a faster metabolism and enhanced fat-burning potential).  However if study subjects were given a high carb (sugary) beverage, like a sports drink, immediately after the workout, this benefit was completely wiped out.  Follow-up studies by the same investigators found that any type of calories post-exercise, but particularly carb calories, seemed to blunt the boost in metabolism exercise normally induces.  The investigators concluded that it appears to be optimal to avoid eating back the calories you burned, especially from carbs, within the first 2 – 3 hours post-workout.