Don't forget that attractiveness is a cultural thing. 200 years ago a well-proportioned woman was considered the picture of beauty - if you were skinny it meant you didn't have the money to eat. Now it costs more to eat healthy than to eat every meal in a fast food restaurant or pull out a tv dinner. This culture still exists in some countries - for a humourous example view the
the trailer for the movie Phat Girlz.
It it important to remember that this is not all to do with people's choices. A significant proportion of that 40 or whatever percent are poor people who are working three jobs and don't have time to go home and cook a healthy dinner for their kids - they'd love to do it if they could but all are able to do is pop over to the drive-thru.