Keel, a psychology professor, and colleagues from Iowa and the Harvard Medical School describe their research in this month's issue of Archives of General Psychiatry.
"Purging disorder is new in the sense that it has not been officially recognized as a unique condition in the classification of eating disorders. But it's not a new problem," Keel said. "Women were struggling with purging disorder long before we began studying it."
If further study supports that it is a distinct disorder, Keel said the American Psychiatric Association could revise its criteria for diagnosing eating disorders. That's important because doctors could then better screen these patients and identify treatments for them. Otherwise, they might be missed because they are normal weight and don't report binge-eating, she said.
"The bottom line is there are women out there right now who have this condition, and very little is being done to figure out why they have this problem or how to help them with it," Keel said.
The study focused on women because they are about 10 times more likely than men to suffer from bulimia, in which people compulsively overeat and then force themselves to vomit, fast, take laxatives or exercise excessively to burn calories.
The dangers of purging disorder are similar to those of bulimia: psychological problems, dehydration, electrolyte imbalances that can affect the heart and kidneys, and potential dental problems because of self-induced vomiting.
Keel's research, conducted from 2001-05, was funded by the National Institute of Mental Health. The study looked at 90 women: 20 women had symptoms of purging disorder, 37 had bulimia and purged after binge-eating, and 33 had no eating disorders. Each woman was interviewed about her eating habits, drank a liquid meal and had blood drawn before and after the meal.
Keel said there were significant differences in the groups when it came to satiety, or feeling full.
In response to the liquid meal, women with purging disorder and those who had no eating disorder had similar levels of a chemical called cholecystokinin. It is released from the upper tract of the small intestine and appears to signal people to stop eating.
"That makes sense, because in terms of eating patterns, women with purging disorder are not actually eating more" than the women who had no eating disorder, Keel said. The bulimic women had lower levels of the chemical.
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The women with purging disorder said they felt much more full after the test meal, and they reported more stomach discomfort than the bulimic women and the women with no eating disorders.
"It kind of begins to provide a clue for why these women may feel a need to purge after eating an amount of food that most people would be fine with. They are actually responding to it differently," Keel said.
The women with purging disorder and the bulimics shared emotional and psychological characteristics, including body image problems, anxiety and depression. Both groups also had strict rules about what they could eat and when, Keel said.
Keel "has helped put purging disorder on the map" as something that should be studied, said Dr. Tim Walsh, professor of psychiatry at Columbia University Medical Center.
Many people with eating disorders don't meet all of the criteria for anorexia or bulimia, "so it suggests that we need additional descriptions to help patients," he said. Walsh heads a work group with the American Psychiatric Association that is charged with revising criteria for diagnosing such disorders.
Leslie Sim, a psychology professor and consultant with the Mayo Clinic's eating disorders program, called Keel a "great researcher" in the field and said her findings were new and interesting.
Sim said current criteria "are kind of limiting for diagnosis and treatment and also for reimbursement by insurance companies."
Keel is recruiting subjects for another study, which she said will look more closely into factors that give rise to the unique response to eating by women who have purging disorder.
On the Net:
University of Iowa: http://www.uiowa.edu/
Mayo Clinic: http://www.mayoclinic.com/
[Associated Press; by Amy
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