Some people have a previous disorder which may increase their vulnerability to developing an eating disorder. Some develop them afterwards. The severity and type of eating disorder symptoms have been shown to affect comorbidity. There has been controversy over various editions of the DSM diagnostic criteria including the latest edition, DSM-V, due in May 2013. Cognitive attentional bias
Attentional bias may have an effect on eating disorders. Attentional bias is the preferential attention toward certain types of information in the environment while simultaneously ignoring others. Individuals with eating disorders can be thought to have schemas, knowledge structures, which are dysfunctional as they may bias judgement, thought, behaviour in a manner that is self-destructive or maladaptive. They may have developed a disordered schema which focuses on body size and eating. Thus, this information is given the highest level of importance and overvalued among other cognitive structures. Researchers have found that people who have eating disorders tend to pay more attention to stimuli related to food. For people struggling to recover from an eating disorder or addiction, this tendency to pay attention to certain signals while discounting others can make recovery that much more difficult.Studies have utilized the Stroop task to assess the probable effect of attentional bias on eating disorders. This may involve separating food and eating words from body shape and weight words. Such studies have found that anorexic subjects were slower to colour name food related words than control subjects.
Also, the media are oftentimes blamed for the rise in the incidence of eating disorders due to the fact that media images of idealized slim physical shape of people such as models and celebrities motivate or even force people to attempt to achieve slimness themselves. The media are accused of distorting reality, in the sense that people portrayed in the media are either naturally thin and thus unrepresentative of normality or unnaturally thin by forcing their bodies to look like the ideal image by putting excessive pressure on themselves to look a certain way. While past findings have described eating disorders as primarily psychological, environmental, and sociocultural, further studies have uncovered evidence that there is a genetic component. Genetics
Numerous studies show a genetic predisposition toward eating disorders. Twin studies have found a slight instances of genetic variance when considering the different criterion of both anorexia nervosa and bulimia nervosa as endophenotypes contributing to the disorders as a whole. A genetic link has been found on chromosome 1 in multiple family members of an individual with anorexia nervosa. An individual who is a first degree relative of someone who has had or currently has an eating disorder is seven to twelve times more likely to have an eating disorder themselves. Twin studies also show that at least a portion of the vulnerability to develop eating disorders can be inherited, and there is evidence to show that there is a genetic locus that shows susceptibility for developing anorexia nervosa.