A lot of things are difficult when you are overweight. Buying clothes, finding a girl-or boyfriend, going to parties, going to the cinema or theatre. Not to mention going to the swimming bath or fitness centre. The result can be isolation and lack of confidence.
Next after smokers, overweight are the most vilified. They take up too much space, they are not in control of their life, they are expensive to the health care system and on top of it all, they brought it on themselves. There are not yet special rooms for overweight people and there are no prohibitions against overweight on workplaces or in the public space. However, overweight are looked down on in the same way as smokers.
Therefore, it is not that strange that you see more overweight people with depressions and other emotional difficulties than normal weight people. The support and acceptance that overweight need is not there.