[makemoniesonlin]

What if someone has a deficit of over 7,000 calories/day for an extended period of time (suppose they eat 3k calories and bike for 14 hours/day)?

[mamon]

To have such enormous deficit you would have to exercise a lot. And of course you breathe faster during the workout so I think it is entirely possible to breathe out more than 2 pounds of CO2 per day. 2 pounds if probably average for a typical person.

[nradov]

That isn't physically possible. You would deplete the nutrients in your muscles within a few hours and then "bonk", unable to continue cycling.