Two more mental disorders which have weight loss as a symptom:
Schizophrenia
In the early phase, people with schizophrenia often seem eccentric, unmotivated, emotionless, and reclusive. They isolate themselves, start neglecting their appearance, say peculiar things, and show a general indifference to life which includes not eating. They may abandon hobbies and activities, and their performance at work or school deteriorates.
Major Depression includes symptoms of:
Significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day.
http://psychcentral.com/disorders/sx22.htm
http://www.helpguide.org/mental/schizophrenia_symptom.htm#early
http://www.webmd.com/schizophrenia/tc/schizophrenia-symptoms