My daughter is very thin and I know that she weighs herself everyday, she also weighs everything before she will cook it, she will just eat like a jacket potato or pasta and that will do her for the day. She also looks at the calories in everything.
A couple of months back she had a pizza and of course the next day she weighed herself and was really upset because she had gained a little weight.
I was at my sisters a couple of weeks ago and told her of my worries about her, apparently my daughter told my niece that she has made herself sick after eating, I then called my doctors who did see my daughter right away, the doc said that she does have an eating disorder and has referred her for help I think to the mental health team which is about a 6 week waiting list.