There are many ways to approach the delusional thoughts but only one appears to be consistently effective. In order to use this method, the person already needs to understand that the eating disorder thoughts are delusional and also at least acknowledge that more logical thoughts exist and would encourage recovery. With that foundation, treatment can move forward.
The core piece of this step in therapy is to create an internal dialogue between the eating disorder thoughts and the healthy thoughts. The ed thoughts have usually felt completely true and also secret for a long time. Exposing them can be emotionally challenging and even scary to admit openly. The healthy thoughts often feel forced and unsure. It takes time for these thoughts to start to seem true and supplant the eating disorder thoughts.
It is also important that both sets of thoughts come from the person struggling with the eating disorder. It's counterproductive for the healthy thoughts to come from someone else. The purpose of the exercise is to practice and express the healthy thoughts and learn to associate oneself with a new way of thinking.
An example of the dialogue can start with the idea that one shouldn't have lunch.
Ed: You don't need lunch today. You're not hungry.
HS: Food is a part of recovery. Hunger is not the issue. Eating to live is the issue. Following the meal plan is crucial to get well.
Ed: You're already fat. You don't need food.
HS: Without food you just end up getting sicker and unable to live your life.
Ed: But you want to be skinny. That's most important.
HS: You've done that before. Then you end up in treatment and unable to make friends or do anything. Life is much more than starving.
Typically the dialogue leads to the conclusion that the eating disorder thoughts only want the person to live for the illness itself. There is no purpose beyond that and it leaves no meaningful life in its wake.
Although this is a hard part of recovery, it is crucial to help combat longstanding delusional beliefs. Making these changes and doing the consistent work is a big part of the reason people can fully recover.