> I didn't know that smoking caused less obesity. I would have thought it was because of monetary reasons.
It does not cause less obesity. It is correlated with less obesity, possibly through suppressed appetite -- but it's also possible that it's actually a reflection of economic background which is also correlated with obesity.
It apparently does cause more alertness (in the same way that coffee does -- enough of it will make you awake and alert, too much will kill you).