I have a little biology lesson for anyone who wants to take medical advice from a writer. I recently was talking to a veteran runner who mentioned something called energy gel. It is basically a sugar compound which is easy to carry, eat and digest. It supplies sugars like fructose, and has meltodextrin which helps with energy absorption as does the carbs present in the gel.
The necessity for energy gel comes from the medical fact that during long periods of working-out such as a marathon your body stops your ability to process food and\or drinks.
The gel comes in a variety of flavors (I've had the Espresso Love and it was better) and is meant to be eaten every 45-60 minutes. This will avoid the crashes after the race. F.Y.I- It is an aquired taste. For more information their website was extremely helpful and user friendly.