David Bickham of the Harvard-affiliated Boston Children's Hospital, who analyzed data on 91 teens ages 13-15, found it's how focused teens are on television programs rather than how long they watch that affects weight gain.
"Increased attention paid to TV was associated with increased BMI," Bickham said in a statement. "We didn't find any evidence that it was the total amount of time spent watching TV, or the time spent playing video games or computers."
Bickham said the teens were paying more attention to food ads, so watching programming without the ads might help reduce their BMI.
The study was published in the journal Pediatrics.