There’s actually been some good news on obesity in recent years. After years of steady increases, new Centers for Disease Control and Prevention data has suggested that rates are beginning to plateau, if not decline slightly.

That data, however, looks like it might be masking a troubling trend: A growing socioeconomic disparity in obesity rates, with most prevention gains being made among higher earners.

New research in this month’s Pediatrics focuses on childhood obesity rates in Massachusetts. It found that, overall, obesity rates held steady for children under 6 between 1999 and 2003, but then dropped by a notable 14.7 percent over the next four years, from a 10.5 percent obesity rate in 2004 to 8.9 percent in 2008.

“The declines in obesity in our sample...suggest that the epidemic of obesity may have peaked among young children around 2003–2004,” the authors conclude.

But that wasn’t necessarily the case when the authors broke down the data for children by socioeconomic status. Among children insured through Medicaid, researchers saw a smaller, 6.9 percent, decline in obesity rates. That’s the population where, arguably, the most work on obesity reduction is necessary: The obesity rate stood at 11.5 percent in 2008, about 2 percent higher than the overall population.

Kids on private insurance, saw obesity rates fall by 17 percent to 8.3 percent in 2008.

To the authors, the smaller decrease in obesity among those on Medicaid “suggests that the coming years may see a widening of socioeconomic disparities in childhood obesity.”