[mikeash]

200g is what a typical sedentary person breathes out in a day.

You can definitely increase your burn rate by way more than 20% with heavy exercise. A Tour de France bicyclist will burn several thousand calories (4,000-7,000 depending on the stage and rider) in only about six hours. For comparison, a typical sedentary person will burn 2,000-2,500 calories per day. It can be physically difficult to eat enough at that rate, and riders lose a substantial amount of weight over the race. (A friend once told me about an endurance cyclist he knew who would eat a big bowl of cereal each morning, except instead of milk he'd use olive oil. Disgusting, but an effective way to get enough calories in.)

It's pretty tough for most of us to achieve anything like that much exercise, of course. Even Tour de France riders only do it for a few weeks at a time.

[k__]

Thanks, that was what I wanted to know.