I agree that it makes social and economic sense to have a healthy society. My opposing point is this: If medical care is a right to be provided by society (the government?), and food too, as you mentioned, shouldn't adequate shelter be included? How about protective clothing for those who live in areas with extreme heat and cold? And what about social networking. We need to socialize to be healthy.
So based on these self-evident rights, we would provide medical care, food, shelter, clothing, and a twitter account  for any citizen who couldn't (or wouldn't?) provide these things for themselves.
Of course, you see where I'm going with this. How long before we have a continually growing segment of the population who aren't productive because they don't have to be. Their basic needs are met.
My personal, anecdotal assessment of human nature leads me to think that eventually there will not be a sufficient number of productive people to support the system. It will collapse catastrophically.