Oct. 2 (HealthDay News) -- The time frame in which gastric bypass surgery can be used to reverse morbid obesity in teens could be much shorter than previously believed, U.S. researchers say.

Their study included 61 teens who had laparoscopic Roux-en-Y gastric bypass at Cincinnati Children's Hospital Medical Center. One year after surgery, overall body mass index -- a measurement of weight in relation to height -- among the teens had decreased by 37 percent. However, because of their weight before surgery, the teens were still considered to be morbidly obese even after they lost weight.

The study, which the authors said was the first to specifically show that teens' starting weight strongly influences their postoperative weight, was published online Sept. 23 in the Journal of Pediatrics.

"Current guidelines for adolescent weight-loss surgery suggest that we begin to consider surgery only after a teen is 80 percent to 100 percent overweight," the study's lead author, Dr. Thomas Inge, an associate professor of surgery and pediatrics at the Cincinnati Children's, said in a news release from the hospital.

"Our new data show that when we intervene when a patient is between 100 percent and 150 percent over ideal weight, we can expect successful resolution of obesity," Inge said. "But by the time the teen is 200 percent over their ideal weight for age, the surgery will reduce their weight substantially, but many of the patients will still remain morbidly obese."

The findings suggest that waiting until teens are "super obese" before performing weight-loss surgery may not resolve their obesity or related long-term medical problems, such as joint damage, the researchers noted.

Doctors "have to do a better job of identifying teens who are gaining enormous amounts of weight quickly and get help for them earlier," study co-author Dr. Stavra Xanthakos, an assistant professor of pediatrics and pediatric gastroenterologist, said in the news release.

When a teen begins to gain weight rapidly, doctors should use a staged approach to manage the weight problem.

"If the weight gain is not effectively stopped with initial nutritional or exercise measures, then even more intensive treatments or programs are indicated, and ultimately some very serious thought has to be given to surgery," Xanthakos added.

SOURCE: Cincinnati Children's Hospital, news release, Sept. 28, 2009