The figure I've heard for Track events like pursuit or team pursuit is 18,000 calories during a full day of competition.
There's a movie of the Race Across America- west coast to east with as many or as few breaks as you want- where the two competitiors were fairly close Pete Penseyres had a special diet of tofu and sprouts, John Howard was having the support crew drive ahead to truck stops for twinkies and big macs.
Howard won. When he was asked later about the horrible diet he said you couldn't make the ride without being in great shape, and what was needed was Big quick calories.
The other one I was impressed by was Francesco Moser doing some early physiological testing. Maxed out every test the docs had and wasn't really working hard. On tests that had driven soccer players and runners to near collapse(over an hour on the three steps thing with only a modest increase in heart rate.). He came back with a bike and ran over an hour with a pulse around 180-185 and a max close to 200. Recovery time was getting back to 140 between the bike and chair, back to his resting of 35bpm in under 10 minutes. He was insanely fit,a bit of a physical oddity and probably doping. Hard to tell which had the most effect. Other top cyclists have an abnormal lung volume and the stuff used at the time helped the blood absorb oxygen.
Steve B