Another thing, single mother household are not new and have always been common throughout time, as have been stepfamilies and blended families. Female headed households can't account for this.
Also, being "feminine" or gay/etc does not give you an eating disorder. There are a lot of there things that make you succeptable to mental illness though... There is evidence that viruses may be a culpret of some metal disorders like schizophrenia and Obsessive compulsive disorder (which has stuff in common with anorexia), emotional truama, lack of coping skills, family history - mental illness is highly inheritable.