Get help fast. It's important that the therapist and dietitian work together. Sometimes the patient isn't willing or ready to address food issues. It's also important that the therapist and dietitian have a good relationship. Eating disorder patients can be secretive and say one thing to the therapist and something else to the dietitian.
Professionals have to be willing to confront patients if they revert to old coping mechanisms.
You cannot force an anorexic to eat, keep a bulimic from purging or make a compulsive overeater stop overeating. Do not concentrate on the food, eating disorders are emotionally based and the behaviors are only a symptom to emotional and stress related problems.