Obese teens generally feel worse than their peers, but after undergoing gastric bypass they usually experience improved mental health, according to a recent study.

"Another important discovery was that some did not feel better," Kajsa Jarvolhm, a researcher and psychologist at Lund University said in a statement. "Just under 20 percent of patients said they still did not feel well after having surgery, and their self-assessments showed symptoms of moderate to severe depression. Thirteen percent showed symptoms of severe depression."

Researchers from Lund University found conducted one of the largest two-year follow-up studies in the world regarding mental health in adolescents who have undergone a form of weight-loss surgery known as gastric bypass.

For the two-year study, researchers collected and analyzed data from 88 Swedish teens between the ages of 13 and 18 years old, which an average body mass index (BMI) of 45.6 prior to surgery. They examined the adolescents in three rounds: before surgery, one year after surgery, and two years after surgery.

"Most young people felt significantly better two years after surgery. On average, they felt like most other adolescents, so their mental health had been normalized," Järvholm said. "There is also a big difference in how weight affected them in various social situations. Two years after the operation, they experienced far fewer limitations than before."

Järvholm believes that it is important to continue studying the group of adolescent patients. She also considers it necessary to provide psychosocial support for young people undergoing gastric bypass surgery, especially those who do not feel better mentally even if they lost weight.

Many operations on young people have been carried out in Sweden, where healthcare is free, compared to in the rest of the world. Other countries, such as Denmark, do not allow weight-loss surgery for patients under the age of 25, and in the United States you need health insurance to cover the procedure.

Researchers said their study, which is detailed in the journal Obesity, is based on an internationally unique and large group of patients.