When obese teenagers lose weight it is often seen as a positive thing, but loved ones could be missing the signs of a budding eating disorder.

A Mayo Clinic study suggested obese teenagers who lose weight are at a higher risk of anorexia nervosa, bulimia nervosa, and other eating disorders. The researchers believe the conditions often go undetected because of weight-loss enthusiasm from the patients' doctors and family members.

"Given research that suggests early intervention promotes best chance of recovery, it is imperative that these children and adolescents' eating disorder symptoms are identified and intervention is offered before the disease progresses," Dr. Leslie Sim, an eating disorder expert at the Mayo Clinic Children's Center, said.

Early intervention seems to be rare in these recently-slimmed-down teens.

"They lost way too much weight and became preoccupied with their eating," Sim told Newsday. "Every thought and behavior really surrounded eating."

The teen's condition is often misdiagnosed. For example: an 18-year-old girl lost 83 pound over the course of three years. She was not eating any fat and had dramatically restricted her diet, the teen was also suffering from dizziness, symptoms of dehydration, and an absent menstrual cycle. Doctor's decided the girl was suffering from, polycystic ovary syndrome (a hormone imbalance that causes similar symptoms), Newsday reported.

In another case, a 14-year-old boy lost 87 pounds in two years. The teen had been working on weight-loss with the support of his family. Despite a presence of several eating disorder red flags, doctor's did not diagnose the boy's condition as such until his mother insisted.

"We think obese kids are at risk for eating disorders because they are getting a lot of media messages that they are not healthy and that there is something wrong with them and they need to change their ways," Sim told Newsday. "And because they are teens, they do extreme things."

Sim recommends that parents regularly ask about their children's eating habits, especially if they are losing weight. Two major warning signs of an eating disorder are avoiding meals with friends and skipping meals altogether.

"Whenever you see a kid losing weight, you have to see exactly how they are doing it," Dr. Metee Comkornruecha, an adolescent medicine specialist at Miami Children's Hospital, told Newsday. "Weight loss at any cost is not a good thing. They have to be doing it in a healthy manner, which means eating the right foods and exercising."

At least six percent of adolescents suffer from eating disorders, Mayo Clinic reported. Over half of all high-school females and 30 percent of males exhibit eating disorder symptoms.

The symptoms can include: "fasting, diet pills, vomiting, laxatives, and binge eating," Mayo Clinic reported.