NOT EVERY TEENAGE girl develops an eating disorder. In fact, most do not, even if they are dissatisfied with their bodies. Similarly, most girls—and boys—who go on diets do not develop eating disorders. The pressure to be thin may be why some teens choose food as a way of dealing with problems, but those who develop eating disorders are responding to a combination of troubling factors in their lives.

The drive to be perfect

Many teens who develop anorexia feel that they must be perfect in all that they do. Dr. Raymond Vath, the psychiatrist who treated Cherry Boone O'Neill, says, "The anoretic maintains ideals and behavioral goals that are absolutely above reproach in order to avoid punishment or rejection. There is frequently a frantic striving to achieve, motivated by underlying guilt and remorse...