If you exercise and are more tired, then you need to eat more. And stay off the sugars and carbs.
Not sure about the carbs though (except sugar, which I try to avoid taking in excess).
I read up that before e.g. running, 3-4 hours before, I eat a heavy full-component meal, and 1-2 hours before, I eat something lighter, with mostly carbs. The effect is light night and day compared to when not thinking about the eating. Can't be reiterated enough, I think.
I would, however, caution on a carb-heavy meal pre-workout. Studies have shown:
1) Consuming carbs pre-workout reduces the fat burned during workout.
2) Consuming protein pre-workout helps preserve muscle protein during exercise.
3) Consuming carbs pre-workout restrains growth hormone release.
4) Carbs elevate serotonin which increases exercise-related fatigue.
5) Higher fat meal will allow more free fatty acids for muscles, and will increase intramuscular triglyceride levels.
All this stuff is from the best book out there: Natural Hormonal Enhancement by Rob Faigin.