This map, out today from the Center for Disease Control, is startling, and good, news. It shows obesity among low-income preschoolers between ages 2 and 4 dropping in 19 states – and increasing in just three.

This and other recent reports suggest that we might just be turning a corner on childhood obesity, an epidemic that has grown steadily in recent years. Lydia DePillis wrote last month about a separate research project from the Robert Wood Johnson Foundation which also found children's waistlines to be shrinking across the country. 

One especially notable fact about today's CDC research is it shows a decline in obesity rates among low-income preschoolers. Until now, many of those reductions have been limited to higher-income kids.

Trying to understand why this is happening — and if its a permanent change — is a difficult task for CDC researchers. They write that "reductions in obesity prevalence might reflect a combination of contributing factors, such as local and state initiatives that focus on the implementation of nutrition and physical activity standards for early care and education programs and efforts to improve healthier food options and physical activity offerings in communities."

The federal government has also made policy changes in recent years, such as aligning the Women, Infants and Children's package of nutritious foods with national dietary guidelines, which "might have led to improved diets among low-income preschool children and their families." Schools have become more aggressive in regulating sugary drinks; an increase in breastfeeding is also one other factor that researchers say could be behind the drop.

Truth is, we don't quite know why obesity is dropping right now. But this CDC report does give some reassurances on one point: that the drop in childhood obesity is indeed happening.