Carbs. Aerobic burns carbs and fat. I'd also be drinking a couple gallons of water all day/night long. I'd also cringe at the thought of 10-15 miles though! I get one heck of a work-out from 3-5.
I normally ran 3-5 miles but my daughter talked me into running the Detroit marathon in October so I've had to increase my mileage. I have a couple of 20 milers to run in Sept to get ready for the race.