SI had an article not too long ago about D1 football lineman...who don't go onto the NFL. They get the "benefit" of training to bulk up, eating 4x fried chickens/ day and all that but then they're done and may not get a lot of support at the transition to normal lifestyle and activity level.
I'm not 100% sure if one actually needs a ton of carbs to exercise as much as one needs regular consumption of quick acting carbs during the activity? All (3) of my 1/2 marathons were around 2 hours and, while I was not "world class", in terms of the input/ output equations, I'm not sure a pro is going to gain a whole lot more "burnoff" by going twice as fast as I do? I skip dinner the night before (portapottyphobia, not "phobia" as much as gross out but I dunno the medical term...) and have had a light breakfast, generally eggs and a piece of toast, which is pretty much what I eat every day.