Teens and young adults with atypical anorexia nervosa can have normal body weights and still be dangerously ill, according to a new study led by researchers at the Stanford University School of Medicine and the University of California-San Francisco.

The research is the largest, most comprehensive assessment to date of normal-weight adolescents with atypical anorexia.

Traditionally, individuals had to be below 85% of their ideal body weight to receive a diagnosis of anorexia nervosa, a disorder characterized by restrictive eating, over-exercising, distorted body image and intense fear of weight gain. But in 2013, a new category of eating disorder was formally recognized: atypical anorexia nervosa. Individuals with this condition meet all other diagnostic criteria for anorexia nervosa but have a normal body weight.

"This group of patients is underrecognized and undertreated," said the study's senior author, Neville Golden, MD, professor of pediatrics at the Stanford School of Medicine. "Our study showed that they can be just as sick medically and psychologically as anorexia nervosa patients who are underweight."

The study, publishing online Nov. 5 in Pediatrics, shows that large, rapid weight loss is the best predictor of medical and psychological problems in patients with atypical anorexia, not their body weight at diagnosis. Dangerously low heart rate and blood pressure, as well as serious electrolyte imbalances and psychological problems, are common in patients with atypical anorexia whose weight is within a normal range, the study found.

The study's lead author is registered dietitian Andrea Garber, PhD, adjunct professor of pediatrics at UCSF.

"The bigger context is that, over the past 30 years, the prevalence of adolescent obesity has quadrupled, and teens are being told to lose weight without being given tools to do so in a healthy way," Golden said. Obese teens who adopt unhealthy behaviors -- such as severe food restriction and extreme exercise -- may initially be praised for weight loss or told not to worry about eating-disorder concerns because they aren't underweight.

"By the time they get to see us, they've lost a tremendous amount of weight, their vital signs are unstable and they need to be hospitalized," Golden said.

Low heart rate, electrolytes

The study compared 50 patients with atypical anorexia nervosa with 66 patients who met traditional diagnostic criteria, including being underweight. Participants were 12-24 years old, and 91% were female. All participants received eating-disorder treatment as part of the study, the results of which will be reported in a future publication.

Before developing an eating disorder, patients with atypical anorexia had higher weight-to-height ratios than typical patients. During their illness, patients in both groups lost the same amount of weight, an average of 30 pounds over 15.9 months. The two groups had equally poor vital signs, including low heart rate and low electrolytes. Cessation of menstruation, a side effect of the disease, was equally common in the two groups. Some members of both groups also had very low blood pressure, although this was more common in the patients with typical anorexia. Atypical patients had worse psychological symptoms, on average.

The researchers used statistical modeling to determine which factors best predicted illness severity. The amount, speed and duration of weight loss were linked with worse illness; body weight at the time of diagnosis was not, they found.

More research is needed to identify what constitutes healthy weight for adolescents recovering from atypical anorexia nervosa, Golden said.

"If a patient was obese, the goal is not to have them regain all the lost weight," Golden said, adding that a mixture of metabolic, hormonal and psychological measures may be needed to define a healthy weight instead.

"If someone gains a bit of weight, regains menses, and is doing well socially, emotionally and cognitively, that might indicate that they are in a place of recovery," he said.

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Other Stanford co-authors on the study are Cynthia Kapphahn, MD, clinical professor of pediatrics; research coordinators Anna Kreiter and Kristina Saffran; and clinical dietitian Allyson Sy. Scientists at UCSF, UCLA and the University of Chicago also contributed to the study.

The research was supported by the National Institutes of Health (grant R01HD082166) and a Leadership Training in Adolescent Health grant from the Health Resources and Services Administration.

Stanford's Department of Pediatrics also supported the work.

The Stanford University School of Medicine consistently ranks among the nation's top medical schools, integrating research, medical education, patient care and community service. For more news about the school, please visit http://med. stanford. edu/ school. html . The medical school is part of Stanford Medicine, which includes Stanford Health Care and Stanford Children's Health. For information about all three, please visit http://med. stanford. edu .

Print media contact: Erin Digitale at (650) 724-9175 (digitale@stanford.edu)

Broadcast media contact: Margarita Gallardo at (650) 723-7897 (mjgallardo@stanford.edu)