Want to Make Your Kid Fat? Take Out His Tonsils

(CBS) If you're worried about your child's waistline, you may want to keep his tonsils in his throat.

That's the surprising conclusion of new research which showed kids who had their tonsils removed increased their body mass index (BMI) from 5 to 8 percent. In six other studies, anywhere from half to all of the kids gained weight.

"This weight gain has been going on for a long time, almost four decades. Now, we need to figure out why it's happening," Dr. Anita Jeyakumar, a pediatric ear, nose, and throat specialist at Cardinal Glennon Children's Medical Center in St. Louis, told MSNBC.

Making sense of the results is no small matter. Tonsillectomy is the most common surgery performed on children in America, with more than 500,000 procedures each year. And up to a third of children are now considered overweight and 17 percent are obese, putting themselves at risk for cardiovascular disease and diabetes later in life.

Children have their tonsils removed for several reasons - most often because they can cause frequent infections of the throat and ears. When swollen, they can also make it difficult to breathe while sleeping. Over the decades, doctors have swayed back and forth about how aggressive to be in removing them.

The new research doesn't offer conclusive reasons for the weight gain. Jeyakumar says kids with swollen tonsils may not be eating as much or parents may overfeed their children after surgery to make them feel better, but neither theory is proven at this point.