How can I tell if my son has an eating disorder?

Posted by Karen

My stepson who is 28 tells me yesterday he thinks my son (17), his half brother is bulmic because he always goes to the bathroom immediately after he eats.  Recently he has had a lot of dental problems-multiple cavities and soft brittle teeth-one of his teeth has chipped.  He has never been overweight.  I'm worried and don't know what to do.  I don't want to take him to the doctor or ask him about it if there's nothing to it.  What do you think?