Just to add context here, this morning I did a 46.4 mile ride in 2:33. The ride included 28 minutes at threshold. I produced 1625 kj, which equates to about the same number of calories burned, depending on which algorithm is used to compute that. Breakfast was coffee and a bowl of Cherrios, and I went through two bottles of full strength Gatorade and another one of plain water. So yes, you do need to take in calories on the ride, but there's no need to go crazy about it.