Eating disorders do seem to mess up the digestive system for the long term.Have you tried an osmotic laxative (not the stimulatory ones that people with eating disorders tend to abuse) which only pulls water into the stool?Sometimes that will keep the stool wet enough to move so even if the GI tract doesn't move it well, it can keep moving it. Some people like Magnesium supplements, other like Miralax.Eating regularly at the same times every day may help and you may be one that needs to eat 3 larger meals (to get more colon movement after a meal) rather than grazing or 4-6 small meals.