I run about three or four miles in the morning before breakfast. A friend of mine says it does and that I should eat an energy bar before starting out on my run. Although it's not advised to run a marathon before breakfast, moderate exercise an empty stomach should do you no harm.
Carbohydrates are the most important food required to meet energy needs for exercise.
These nutrients, which we get mainly from plants, are stored in our muscles and liver as glycogen. After just a night's sleep, however, there should still plenty of glycogen in your muscles and liver to meet the energy demands of most routine exercise. There is surely enough to keep you going for three or four miles. If, of course, you are eating a normal diet. They are convenient and portable foods.