...you are referring to when you say that the government is making its business whether you "go scaling some rock face somewhere, or sit on the couch and eat Big Macs all day". 

And then, take a look at government's existing medical insurance program, Medicare.  Do they make you pay a different amount based on your lifestyle?  No they do not.  You pay the same flat rate as everyone else, regardless of whether you run marathons or smoke 5 packs of cigarettes a day.

On the other hand, the private insurance companies most certainly make it their business to know what kind of shape you're in-- and time and time again they have used their power to act on that information, for example kicking sick people off the rolls and denying coverage for preexisting conditions.