Well I don't know about that but there is a famous experiment where people are put in front of a distorting mirror that makes them look fatter or thinner. They are asked to adjust it to show them correctly.
The vast majority of women will adjust it to a point that shows them as fatter than they are and men will typically adust it to show them as thinner.
I think that if you are approaching this from a viewpoint of optics then you are missing the point.
The real issue is how fat or thin people think they are or think that they should be and where they get this idea from.