What causes teenage eating disorder in girls?

Family disease: Adolescents model their behavior, either in identification or rebellion against their families. Disordered eating may occur in families with eating disorders or other addictions.

Nature/nurture: This is a great question & many are not aware of recent research advances. Eating disorders have among the highest genetic component of any psychiatric disorder. For anorexia, losing weight in ways that are harmless to others, likely leads to a downward spiral where compulsive weight loss behaviors take over. In bulimia, the intensity of uncontrolled binges likely triggers purging.

Parents do not cause eating disorders: Eating disorders are not caused by modeling behavior or by the media. They are brain disorders of unknown etiology (cause) which do run in families (are heritable) like many other diseases such as high cholesterol. They are often diagnosed in adolescence, but may actually have actually begun earlier. They can also present for the first time in adulthood. Families do not cause eating disorders and sufferers do not choose to have them.