Not rail-thin? A teen may still be stuck in a serious eating disorder. Researchers report that dangerous eating behaviors may be present in teens that show no indication of a problem through their body weights. In fact, they found an almost 6-fold rise in teen patients who were at normal weights but exhibited every other indicator for anorexia.

Eating disorders such as anorexia nervosa and bulimia can cause loss of body weight to the point that the patient appears abnormally thin. However, being underweight is not a necessary criterion for diagnosing these diseases.

“Emaciated bodies are the typical image portrayed in the media of patients with restricting eating disorders such as anorexia nervosa,” said lead author Melissa Whitelaw, a clinical specialist dietitian at The Royal Children’s Hospital in Melbourne, Australia. “This paper highlights that it is not so much about the weight but the weight loss that can lead to a serious eating disorder. The complications of malnutrition can occur at any weight.”

The report was published Monday in the journal Pediatrics. In the study, 99 teens aged 12 to 19 were assessed for “eating disorders not otherwise specified,” or EDNOS-Wt, which includes the presence of anorexia symptoms and absence of underweight. Only eight percent had EDNOS-Wt in 2005 compared with 47 percent in 2009.

“I was surprised to see how much it increased,” Whitelaw said. “I was also surprised at how similar they were not only physically but also psychologically. Everything about them was anorexia except that they don’t look really skinny.”

Experts caution that by looking only at body weight, serious eating disorders in teens may be overlooked.