How long will you have to be like this to be officially diagnosed with anorexia?

Anorexia: Takes a while, due to secretiveness of the eating patterns, until it gets severe & obvious enough that it cannot be concealed anymore, or when starts to affect physical health & appearance in obvious manner.

It not the the time: There are three basic criteria ; 1.Restriction of food intake that leads to markedly low body weight for age, gender, developmental course and medical health 2.An intense fear of gaining weight or becoming fat, or persistent behavior that prevents weight gain, despite the person being significantly underweight 3.Self-perception that is grossly distorted, excessive emphasis on body weight , shape