The paper is the latest in a growing field of research examining the effects of modern life on the trillions of beneficial bacteria living in and on the human body.

While the research doesn't definitively prove that the drugs make children gain weight, it's consistent with earlier studies in humans and animals linking antibiotics to obesity, says coauthor Charles Bailey, an assistant professor at Children's Hospital of Philadelphia.

Many scientists are now concerned that exposure to antibiotics -- from medication, food or even tap water -- has the potentiall to kill off some of the beneficial bacteria that may protect people from chronic diseases, Bailey says.