"This is the first report to show many states with declining rates of obesity in our youngest children after literally decades of rising rates," says CDC director Tom Frieden.
Previous CDC estimates have shown that about one in eight preschoolers is obese in the U.S., and preschoolers who are overweight or obese are five times more likely than their normal-weight peers to be overweight or obese as adults.
Researchers analyzed data of about 11.6 million children ages 2 to 4 in federally funded maternal- and child-nutrition programs, which came from the Pediatric Nutrition Surveillance System.
A total of 19 states and territories reported small but significant downward trends in obesity among low-income preschoolers.
The largest percentage point decrease in obesity prevalence was in the U.S. Virgin Islands, which dropped from 13.6 percent in 2008 to 11 percent in 2011. Florida, Georgia, Missouri, New Jersey and South Dakota had the next largest decreases in obesity, seeing declines of at least 1 percentage point.
There was no change in obesity rates between 2008 and 2011 in 20 states and Puerto Rico. Colorado, Pennsylvania and Tennessee saw their obesity rates rise during that period.
The report credits changes in the nutritional guidelines for the Women, Infants, and Children (WIC) program, increased breastfeeding and increased social awareness of healthy eating through programs including First Lady Michelle Obama's "Let's Move!" campaign.
Obesity rates may be falling for the first time in a generation, but the prevalence of obesity among preschool children had already doubled in recent decades. The CDC report recommends continued prevention efforts.