[danlitt]

I guess when you say "work" you mean precisely mechanical work. If so, I don't think it is implied anywhere that the work "comes from nowhere". If a person is doing mechanical work then that work must come from respiration, ultimately. There is nowhere else for it to come from. If a person does 2000 calories of mechanical work and consumes 2000 calories of energy then there is nothing left over for anything else, and they would lose weight one way or another. But this is much more extreme than what was observed, or what happens when a person ordinarily does exercise.

The "Energy paradox" is not a logical paradox at all. It is just a confusing fact. The observed fact was that two different groups with apparently very different activity levels respire almost exactly the same amount. In other words, that an increased, but not necessarily extreme, level of mechanical work does not appear to correlate with an increased level of calorie burn. Not just that the relationship is non-linear, that the relationship does not seem to exist at all (at the measured level of exercise).

I was very careful with my words this time, hopefully there is no more misunderstanding. I think we still disagree unless by "very significantly increase exercise" you mean something like running multiple hours per day every day.

[jahnu]

No misunderstanding, thanks for your reply. It's been a nice wee sub-thread going on here. Food for thought ;)