Now there's more proof to show that patients with anorexia can't tell how thin they've actually become.
Researchers from the University Hospital of Lille in France took a new approach to asking anorexic patients about how they perceived their body size. They used a projector to shine the outlines of doors of different widths on a wall and asked participants whether they would be able to fit through them. Then, researchers asked patients whether someone standing nearby would be able to fit through the same openings.
Although the 25 women without anorexia nervosa were able to answer correctly in both scenarios, the 25 women who had anorexia were only able to answer correctly when they were deciding whether someone else could fit, according to the study published in the journal PLOS ONE.
"I think it's really fabulous that these researchers are able to provide scientific proof of what people who have worked with these patients have known for a very long time," said Dr. Elizabeth Frenkel, a supervising psychologist at the Princeton HealthCare System's eating disorder program. "They're trying to demonstrate that you can show a clinical and statistically significant difference between people who have these disorders and people who don't."
Psychologists said it isn't "new news" that anorexia patients have body dysmorphic disorder -- a preoccupation with "defects" in their body shape that aren't really there -- but it sheds light on an interesting piece of the anorexia puzzle.
"It's one of those compelling phenomena where you have a person who appears to be completely cognitively intact," said Phillip Levindowsky, a psychology professor at Harvard Medical School. "How could they be so off in their ability to make these judgments?"
Although this study proves what doctors have been seeing for years, the research is still in its early stages. Dr. Cynthia Bulik, who directs the University of North Carolina's Eating Disorders Program, said a study of only 25 anorexic patients and 25 controls is not enough to draw conclusions, so the researchers' work will have to be replicated.
The researchers in France who authored the study were not available for comment.
"It is an interesting study using interesting methodology that gives us directions for future research to further clarify the process of what is happening during these evaluations," she said.
Dr. Susan Albers, a psychologist who works at the Cleveland Clinic, said no matter how many times a patient hears how thin she (or he) has become, the patient doesn't believe it. In fact, hearing that they don't see their body accurately is often frightening and causes the patient to become defensive.
Albers said anorexic patients are often intelligent high-achievers.
"They genuinely know what they feel," she said.
Bulik said she generally has to "agree to disagree" with her patients on the subject because they just don't experience their size the way outsiders do.
"A good example is that we all have different pain thresholds, and it is impossible to experience someone else's experience of a pain level," Bulik said. "Someone might find a needle stick to be extremely painful. If you say to them, 'Ah, c'mon, that doesn't hurt,' you are trying to impose your experience on them and you are not validating the fact that they are feeling things differently than you."
So she and Albers remind patients that they do not share the same perception as everyone else. Albers added that the study will be helpful to hand to patients and their family to explain body dysmorphia in "black and white."
Frenkel said it's difficult to alter a patient's body image, so she teaches patients coping mechanisms, which help with recovery. Over time, patients can regain a healthier body image.
The disorder can last six months or a lifetime, Bulik said, adding that anorexia has the highest mortality rate of a psychiatric disorder. A quarter of all patients relapse or have chronic anorexia, she said.
Although some professionals suggest that eating disorders may stem from serotonin problems in the brain, there is no "gold standard" of care known to produce a cure, Frenkel said. Part of that is because research on eating disorders is still in its early stages.
Although 10 million people suffer from anorexia nervosa, only $7 million has gone toward research, according to the National Eating Disorders Association. That's compared with 4.5 million people who have Alzheimer's disease and 2.2 million people who have schizophrenia, which get $412 million and $249 million toward research, respectively.
Dr. Shari Barnett, a resident in Internal Medicine at Temple University who works with the ABC News Medical Unit, contributed research to this article.