[card_zero]

That's a good read. But one of the processes competing for calories is the immune system.

> If you take somebody who is really sedentary and you get them exercising, what happens? Things like inflammation, which is your immune system being overactive, goes down. [Also cortisol level when under stress, and reproductive hormone levels, go down.]

So that puts a small hole in the "exercise helps the immune system clear up cancer" theory. Maybe it in fact stops the immune system causing cancer. Or maybe it does both things, since biology is messy and the immune system might have multiple energy budgets for all I know.