there is a difference between someone who is thin and works out verses someone who is thin and sedintary. In my moto, I state that i would rather be fat and fit than thin and not (fit). I don't equate thin with unhealthy. Many people are thin and fit, but there are those who are not. Most people equate fat with unhealthy, but there are some out there that are fit, though they have extra pounds.
I have to say, I obviously am not a thin person, but when I went to the doctor yesterday and the lady wieghed me and questioned the validity of what she saw, It made me feel pretty good.