[patrick451]

I'm not so sure. I've seen some rat studies on longevity and fitness with pretty surprising results. Obese, idle rats were the shortest lived (not surprising). But surprisingly, fit, active rats actually had shorter life spans than anorexic, lazy rats. Who knows if it generalizes to humans, but results like this always make me skeptical that first principles thinking will hold up in complex biological systems.

[strken]

I think this is also first principles thinking going wrong: calorie restriction increases rat longevity and (presumably) reduces rat movement, and there's no good way to make calorie-restricted rats voluntarily do more exercise without introducing confounding variables, but that doesn't show whether a calorie-restricted human would live longer if also doing some exercise.