Why would this be? The obvious answer is that young ultra Orthodox girls trying to attract the best grooms are expected to stay very thin; we've written about this recently. But some patients seem to see "eating disorders as a more culturally sanctioned form of rebellion in a religion where smoking and drinking are discouraged". And there are also issues stemming from the religion itself - not just the culture: the increased emphasis on food and food rituals in Judaism seems to be a "breeding ground" for an eating disorder.
Along similar lines,
Eating disorders are traditionally associated with attempting to control at least one facet of one's life when life feels out of control. I wonder whether it is not a coincidence that eating disorders seem to be (even) more common amongst women in the religious world, who live in a relatively regimented society, with fewer opportunities to rebel or express their individuality than their secular peers.
Leaving treatment and re-entering the tight-knit Orthodox culture also presents hurdles. For many, fasting on Yom Kippur or another holiday could cause them to relapse, but patients worry about judgment from others.
[Hillary] Waller [who is in fact Conservative - MS] felt guilty one holiday as she loaded her plate at a salad bar shortly after leaving treatment. She felt isolated from the community, unable to join in the ritual fast with the rest of her congregation, until she realized her greater sacrifice would be eating.
"For me it became the opposite. I had to give into all the things that everyone else had been giving up," Waller said. "That was the lightbulb that reconciled the Jewish dilemma I was facing with needing to be in recovery."