Comment by snowwrestler

Total body calorie expenditure seems decoupled.

Exercise obviously must burn calories because work is being done. The body can’t overcome physics.

The nuance, and the surprising thing, is that other parts of the body seem to adjust their energy levels to compensate. If you don’t do a lot of exercise, something else burns calories. If you do exercise, the “something else” burns less.

What is the something else? That’s the mystery that still needs to be solved. And by extension, what are the limits of the something else? After all, there are well-documented examples of extreme athletes who consume lots of calories without gaining mass.