Rate of Childhood Obesity Falls in Several Cities At William H. Ziegler Elementary in Northeast Philadelphia, students are getting acquainted with vegetables and healthy snacks. PHILADELPHIA - After decades of rising childhood obesity rates, several American cities are reporting their first declines. The trend has emerged in big cities like New York and Los Angeles, as well as smaller places like Anchorage, Alaska, and Kearney, Neb. The state of Mississippi has also registered a drop, but only among white students. "It's been nothing but bad news for 30 years, so the fact that we have any good news is a big story," said Dr. Thomas Farley, the health commissioner in New York City, which reported a 5.5 percent decline in the number of obese schoolchildren from 2007 to 2011. The drops are small, just 5 percent here in Philadelphia and 3 percent in Los Angeles. But experts say they are significant because they offer the first indication that the obesity epidemic, one of the nation's most intractable health problems, may actually be reversing course. The first dips - noted in a September report by the Robert Wood Johnson Foundation - were so surprising that some researchers did not believe them. Deanna M. Hoelscher, a researcher at the University of Texas, who in 2010 recorded one of the earliest declines - among mostly poor Hispanic fourth graders in the El Paso area - did a double-take. "We reran the numbers a couple of times," she said. "I kept saying, "Will you please check that again for me?" " Researchers say they are not sure what is behind the declines. They may be an early sign of a national shift that is visible only in cities that routinely measure the height and weight of schoolchildren. The decline in Los Angeles, for instance, was for fifth, seventh and ninth graders - the grades that are measured each year - between 2005 and 2010. Nor is it clear whether the drops have more to do with fewer obese children entering school or currently enrolled children losing weight. But researchers note that declines occurred in cities that have had obesity reduction policies in place for a number of years. Though obesity is now part of the national conversation, with aggressive advertising campaigns in major cities and a push by Michelle Obama, many scientists doubt that anti-obesity programs actually work. Individual efforts like one-time exercise programs have rarely produced results. Researchers say that it will take a broad set of policies applied systematically to effectively reverse the trend, a conclusion underscored by an Institute of Medicine report released in May. Philadelphia has undertaken a broad assault on childhood obesity for years. Sugary drinks like sweetened iced tea, fruit punch and sports drinks started to disappear from school vending machines in 2004. A year later, new snack guidelines set calorie and fat limits, which reduced the size of snack foods like potato chips to single servings. By 2009, deep fryers were gone from cafeterias and whole milk had been replaced by one percent and skim. Change has been slow. Schools made money on sugary drinks, and some set up rogue drink machines that had to be hunted down. Deep fat fryers, favored by school administrators who did not want to lose popular items like French fries, were unplugged only after Wayne T. Grasela, the head of food services for the school district, stopped buying oil to fill them. But the message seems to be getting through, even if acting on it is daunting. Josh Monserrat, an eighth grader at John Welsh Elementary, uses words like "carbs," and "portion size." He is part of a student group that promotes healthy eating. He has even dressed as an orange to try to get other children to eat better. Still, he struggles with his own weight. He is 5-foot-3 but weighed nearly 200 pounds at his last doctor's visit. "I was thinking, "Wow, I'm obese for my age," " said Josh, who is 13. I set a goal for myself to lose 50 pounds. Nationally, about 17 percent of children under 20 are obese, or about 12.5 million people, according to the Centers for Disease Control and Prevention, which defines childhood obesity as a body mass index at or above the 95th percentile for children of the same age and sex. That rate, which has tripled since 1980, has leveled off in recent years but has remained at historical highs, and public health experts warn that it could bring long-term health risks. Obese children are more likely to be obese as adults, creating a higher risk of heart disease and stroke. The American Cancer Society says that being overweight or obese is the culprit in one of seven cancer deaths. Diabetes in children is up by a fifth since 2000, according to federal data. "I'm deeply worried about it," said Francis S. Collins, the director of the National Institutes of Health, who added that obesity is "almost certain to result in a serious downturn in longevity based on the risks people are taking on."