Running for a long period of time puts pressure on your body to produce energy to keep you going and keep your performance up. When you go for a short run (less than an hour) most of your energy comes from stored muscle glycogen. However if you are running longer this reserve gets depleted so the sugar in your blood and liver glycogen become more important. Fueling with carbs during longer runs will prevent you from running out of energy and help maintain performance.
So how do I refuel when running?
Well, one easy way to get carbs while running is through sports drinks. If you would prefer solid foods they need to be small and easy to digest such as energy bars or sports jelly beans which are designed for long distance runners to eat while running. Some runners prefer sweets like gummy bears so try experimenting and see what you prefer on your longer runs.
So how much should I eat on the run?
You should be taking in about 100 calories after half an hour of running then another 100 calories every 40-45 minutes after that. This will vary per person, depending on size and speed.
Listen to your body, and if you feel hungry or low on energy, take a break and consume other calories.