If your blood sugar is under control, how much you need to eat depends mostly on how long and hard you plan to exercise. Start with some healthy carbs. Your body will digest them slowly. Mix in a little protein, healthy fats, and some fiber. That should keep you -- and your blood sugar -- revved up for the length of your sweat session. Try a dollop of tuna salad with a few whole-grain crackers, a frozen banana topped with almond butter, or avocado and cheese in a lettuce-leaf wrap.