Refueling after the marathon is essential to help your body recover quickly. Eat or drink about 200 or 300 calories of carbohydrates and some protein within an hour of finishing the marathon. The carbs refuel your muscles with glycogen, and the protein will help repair your muscles. Eat a full meal as soon as you are able to continue the recovery process. And remember to slowly drink fluids to rehydrate after you cross the finish line.