In fact, in the study, physical activity had no impact on weight change. However, weight clearly led to less activity.
The study states that "The implications are profound for public health policy, because the physical activity of children (crucial to their fitness and well-being) may never improve unless the burgeoning levels of childhood obesity are first checked. If this cannot be achieved through physical activity, the focus has to be on what--and how much--children consume."
Of course being active has a slew of health benefits associated with it, but this is food (pun intended) for thought for those hoping to reverse the obesity trend, isn't it?