You’re not going to make it far if you don’t have fuel, because your body burns through its glycogen stores quickly, so it’s important to eat before a long run. A Tufts University study found that the ideal balance for a pre-run meal is 60 percent carbohydrates, 20 percent protein, and 20 percent fat. Give yourself time to process what you ate before you head out.
According to the study, “If you eat a full meal, you want to give yourself 3-4 hours before working out. A smaller meal takes between 2-3 hours, and a snack one hour.” Long training runs are also a good time to test what you want to eat during your race, because if you bonk or cramp, there’s no one timing you. Bring small snacks, and test what helps your energy level without sinking in your gut.