Eating disorders are mental illnesses defined by abnormal eating habits that negatively affect a person's physical or mental health. They include binge eating disorder where people eat a large amount in a short period of time, anorexia nervosa where people eat very little and thus have a low body weight, bulimia nervosa where people eat a lot and then try to rid themselves of the food, pica where people eat non food items, rumination disorder where people regurgitate food, avoidant/restrictive food intake disorder where people have a lack of interest in food, and a group of other specified feeding or eating disorders. Anxiety disorders, depression, and substance abuse are common among people with eating disorders. These disorders do not include obesity. The cause of eating disorders is not clear. Both genetic and environmental factors appear to play a role. Cultural idealization of thinness is believed to contribute. Eating disorders for example affect about 12% of dancers. Those who have experienced sexual abuse are also more likely to develop eating disorders. Some disorders such as pica and rumination disorder occur more often in people with intellectual disabilities. Only one eating disorder can be diagnosed at a given time.