I think the difference is that somebody with a true eating disorder such as anorexia nervosa will still see themselves as overweight regardless of how much weig

I think the difference is that somebody with a true eating disorder such as anorexia nervosa will still see themselves as overweight regardless of how much weight they lose. To the point they look like someone who just walked out of a prison/war camp and they still see fat in the mirror where it just doesn't exist. The parent comment sounds as though he his happy with his lifestyle and weight. What really defines it being a disorder is that the person is never happy and always feels they need to lose more regardless of what anyone around them says. I agree with your sentiment that people should enter such fasting regimes with immense caution (it could be a slippery slope for some), but I also agree with the parent that he is probably not suffering such a disorder.