How can societal and environmental factors contribute to the emergence of an eating disorder in adolescents?

Societal factors would involve movies, magazines, news, celebrities all of which promote ultra skinny women to the point women think its the normal and not as fringe as it is, women come in all sizes and shapes all of which are extremely desirable to me, environmental factors would involve say a role model around them that was ultra skinny, say their mum, or sister but they themselves are not like that, they get to thinking that is the norm from what is around them, whichever factors you consider they are both forms or brainwashing and are completely unhealthy, how government allows half of what goes on in society is beyond me.