Not so long ago, say 150 years and earlier, it was ok to be fat. In fact, fat people were considered healthier than skinny people. Why? First, fat people were likely to have higher incomes. More income means more food and easier lifestyles. Second, skinny was associated with poverty and ill health. Poverty was associated with diseases such as tuberculosis (then called "consumption" and untreatable). There was a reason why artists 350 years ago, such as Rubens, used fat women as models. I would also add that people had a different idea of what was "fat" in those days. What we consider "fat" today would have been viewed as average, even thin. Body image was also less an issue 150 years ago because people wore much more clothing.
Today, if one is "fat" then one is likely to be viewed as unhealthy, even poor. Our mass media projects super-thin as a desirable attribute. It is a sin, however, to judge people on this and similar attributes. I know plenty of wealthy fat people (mostly lawyers). The time may yet come when "fat" is cool again, and, retribution will be sweet.