I don't think the hardest sports consume that many calories. I played football in high school and though I practiced very hard I'd be a fat ass eating 6 a day. I ate a whopper or QP maybe 2-3 times a week because it was quick cheap food before practice.
Michael Phelps eats over 10,000 calories a day or so. After eating 8 Whoppers, he would still have 6,000 calories more to eat.