Diets, exercise and behavioral therapy almost never solve their weight problem, said Dr. Stephen R. Daniels, pediatrician in chief at Children’s Hospital Colorado. Moreover, an obese adolescent is almost certain to become an obese adult. The grim prognosis, “debunks the wishful thinking that they will outgrow it,” Dr. Michalsky said.

Of course the best option would be to prevent kids from becoming obese in the first place, but that is not so easy. There seems to be a strong genetic component that is not easily overridden. Most of the teenagers who have the surgery have a parent who also is extremely obese, said Margaret H. Zeller, a professor of pediatrics and psychologist at Cincinnati Children’s Hospital whose research focuses on adolescents with severe obesity. Dr. Morton has operated on patients from three generations in some families.

But despite their qualms about possible medical problems with bones or other body systems in the future, many researchers and surgeons say those concerns are dwarfed by the consequences of being an obese teenager.

“I am less concerned about osteoporosis than that their lives will be completely destroyed if they don’t get some serious weight off,” said Dr. Lee M. Kaplan, the director of the weight center at Massachusetts General Hospital. By completely destroyed, he adds, he means “medically, socially and economically.”

“I’ve had many patients tell me they’d rather be dead,” than remain fat, Dr. Morton said.

In almost every aspect, life for very obese teenagers is “significantly impaired,” Dr. Zeller said. These difficulties, Dr. Zeller noted, are piled onto the normal angst of adolescence.

“It’s not just that people make them feel uncomfortable,” she said. The physical effort of carrying the weight around can make simple tasks arduous, like walking from one area of a high school to another or sitting at desks too small for them. Many have sleep apnea, making it difficult to stay awake in class. And, she said, “inside, they are feeling ashamed.”

Although not every obese teenager feels isolated and friendless, many, including Aliayha, do. She asked to be home-schooled, but her mother, Cristina Carrasco, refused.