After years of hearing about alarming increases in states’ obesity rates, it was nice to get some good news: CDC reports that the percentage of low-income preschool children classified as obese has declined in 19 states. (Height and weight data came from 11.6 million children aged 2-4 participating in the Pediatric Nutrition Surveillance System, which monitors the nutritional status of low-income children. Children whose body mass index was at or above the 95th percentile on CDC’s growth charts were classified as obese.)

Improvements among obesity rates of school-aged children have been reported in some areas, but, as the New York Times’ Sabrina Tavernise notes, that progress was localized and largely confined to children from white and middle-to-upper-class families. Tavernise reports that experts haven’t reached a consensus about what’s behind the recent decline in several states’ preschool obesity rates:

Children now consume fewer calories from sugary beverages than they did in 1999, [CDC researcher Heidi] Blanck said. More women are breast-feeding, which can lead to healthier weight gain for young children. Federal researchers have also chronicled a drop in overall calories for children in the past decade, down by 7 percent for boys and 4 percent for girls, but health experts said those declines were too small to make much difference.

Another explanation is that some combination of state, local and federal policies aimed at reducing obesity is starting to have an effect. Michelle Obama has led a push to change young children’s eating and exercise habits and 10,000 child care centers across the country have signed on.

Many scientists doubt that anti-obesity programs actually work, but proponents of the programs say a broad set of policies applied systematically over a period of time can affect behavior.

“We can’t prove what are the changes in environment and policy that led to” the declining rates, [CDC Director Thomas] Frieden said. But he added that it was hard to believe that the government policies now in place “aren’t having a big role here.”

Tom Baranowski, a professor of pediatrics at Baylor College of Medicine who has been skeptical about government interventions, said obesity has as much to do with genes as it does with behavior. “It could be that we are hitting some sort of a biological limit,” he said, in which “all those who are genetically predisposed to being obese already are.”

We should certainly be investigating the effectiveness of different policies and programs at reducing obesity in different groups, and I expect we’ll see more research addressing this question in the coming years. At the same time, many of the interventions that potentially reduce obesity can also help public health regardless of whether they result in more people with BMIs < 95th percentile. Here are the steps CDC’s accompanying fact sheet recommend for state and local officials:

• Create partnerships with community members such as civic leaders and child care providers to make community changes that promote healthy eating and active living.
• Make it easier for families with children to buy healthy, affordable foods and beverages in their neighborhood.
• Help provide access to safe, free drinking water in places such as community parks, recreation areas, child care centers, and schools.
• Help local schools open up gyms, playgrounds, and sports fields during non-school hours so more children can safely play.
• Help child care providers use best practices for improving nutrition, increasing physical activity, and decreasing computer and television time.

Eating a nutritious diet and exercising are healthy behaviors that we should encourage in everyone, whether or not they reduce obesity. As CDC notes on its Physical Activity web page, exercising regularly can decrease the risk of cardiovascular disease, type 2 diabetes, some cancers, and depression. Fruits and vegetables provide vitamins, minerals, and fiber important for good health. Interventions like pedestrian and bike paths, safe play areas, and farmers’ markets making fruits and vegetables more accessible may or may not bring down obesity rates; if they increase physical activity and consumption of healthy foods, though, they’re good for public health.

CDC’s latest finding lets us know we may be on the right track for reducing obesity — and, more importantly, diabetes and cardiovascular problems for which obese people are at an increased risk. We still have a long way to go.