NEW YORK — Teenagers who undergo gastric-bypass weight-loss surgery lose bone in the 2 years following the procedure, a new study shows.

"The good news is they started out with bones that were far heavier than normal," said Dr. Thomas Inge, a researcher in the study and an associate professor of pediatrics and surgery at Cincinnati Children's Hospital Medical Center.

"After that (bone) loss, they end up about normal for their age," he told Reuters Health.

The long-term effects of the bone loss - and whether it levels out -- are unknown.

Inge and his colleagues measured the bone density, or bone hardness, of 61 teens who underwent the most common form of gastric bypass surgery.