Obesity rates for Philadelphia schoolchildren fell significantly over four years, suggesting that the sort of steps taken here might help reverse a national epidemic. The "environment" -- price, advertising, purchasing habits, and myriad other factors -- is clearly the culprit in the obesity epidemic, said Gary Foster, director of Temple's Center for Obesity Research and Education. “So if we blame the environment for the last 30 years," said Foster, "we've got to credit the environment" for the improvement.