Well, to read your question, tells me you are concerned for someone.
To answer your question from a recovering anorexic point of view - it is a daily fight!
1). Avoidance of foods types and calorie counting ;
2). Avoidant of social gathering with fear of food being present ;
3). Wearing of baggy clothing to hide thinness ;
4). Mood swings ;
5). Lying and deception surrounding food and fear of getting caught out ;
6). Exclusion from people in general ;
7). Excessive exercising. ;
8). Some use diet pills etc ;
9). Difficulty holding relationships due to severity of disorder.
Just some things to look out for.
Hope this helps you