Check this out http://www.businessinsider.com/how-many-calories-cyclists-bu...

"Each day participants ride, on average, about 100 miles and burn some 6,071 calories"

As a competitive, but still amateur cyclist I would do something in this ballpark almost every day. Hence 3000 - 5000 calories. And I'd often run for an hour or play soccer on top of this since I wasn't a pro.

I did spend a lot of hours on the bike, as serious athletes tend to do. Years of experience with myself and many other national caliber athletes tells me that we do in fact get sick from strenuous exercise, all the time.