Done right, carbo-loading can give your body the energy it needs to power you through a long workout or race, says Michele S. Olson, PhD, professor of exercise science at Auburn University at Montgomery. But a bottomless bowl of spaghetti may not be your best bet.
Instead, the day before the event, eat moderate amounts of nonrefined carbs like fruits, veggies, and whole grains throughout the day. In fact, it’s a good idea to ramp up your nonrefined-carb intake several days or even weeks before the race, so your body can get used to the increased levels of fiber in your diet. Cant plan that far ahead? For a smaller (but still helpful) energy boost, eat some fruit and whole-grain cereal with skim milk three hours before you head out.
If you’re attending a pre-marathon pasta dinner (a fun—and quite filling!—traditional event often hosted by the race organizers), eat up: You’re certainly going to burn through those calories the next day. But eat only until you’re full—not stuffed—to avoid digestion problems that may slow you down.
Food – Health.com