No you do not have to be thin to be healthy, a thin person can also be unhealthy. People's mass, BMI (body mass information) basically tells if your healthy or not given just your age and mass but this is simply not accurate at all. I've read articles about how obese isn't always unhealthy. As long as you still have the required or liked 1-2 hours of physical movement, even like walking around the house or doing anything physically, you can be considered healthy. You can be healthy so long as your movement is level and your blood is flowing enough to the point where fat doesn't block it now this doesn't have to do with just obesity in general, just fat that has not activity. Some people do naturally have a wider build and anyone can be healthy or beautiful.