Have you ever felt the "wind go out of your sails" halfway into your workout? Glycogen stored in the liver and muscle tissue is a primary fuel for exercise. During exercise, glycogen is quickly depleted, leaving one feeling fatigued.
  
To increase your body's capacity for glycogen storage, give yourself a "sweet reward" within 15-20 minutes after your workout. While simple carbohydrate (sugar) consumption is usually not recommended as part of an optimal diet, this is the one time when simple sugars can give you the most benefit.
 
So go ahead and have a (small) treat! You deserve it, and your body can use it!