Despite reports in recent years suggesting childhood obesity could be reaching a plateau in some groups, the big picture on obesity rates for children ages 2 to 19 remains unfavorable.

Three decades of rising childhood obesity continued their upward trend in 2016 according to a new analysis from Duke Health researchers. The findings, which appear Feb. 26 in the journal Pediatrics, show 35.1 percent of children in the U.S. were overweight in 2016, a 4.7-percent increase compared to 2014.

"About four years ago, there was evidence of a decline in obesity in preschoolers," said Asheley Cockrell Skinner, Ph.D., lead author and associate professor of population health sciences, who is also a member of the Duke Clinical Research Institute (DCRI). "It appears any decline that may have been detected by looking at different snapshots in time or different data sets has reversed course. The long-term trend is clearly that obesity in children of all ages is increasing."

The data are based on body-mass index (BMI) data for 3,340 children participating in the National Health and Nutritional Examination Survey (NHANES) in 2015-16, a large database updated every two years. Researchers examined data back to 1999 that includes 33,543 children.

The researchers identified notable spikes between 2014 and 2016 in obesity for preschool boys, which rose from 8.5 percent to 14.2 percent, and girls aged 16 to 19, whose rates of obesity jumped from 35.6 percent to 47.9 percent.

Boys and girls aged 16 to 19 had the highest rates of any age group in 2016, with 41.5 percent considered overweight, defined by the Centers for Disease Control and Prevention (CDC) as having a BMI at or above the 85th percentile for age and sex. Among these 16-to-19-year-olds, 4.5 percent have Class III obesity, the highest of three categories defined by the CDC.

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Both Class II and Class III are considered severe and are linked with greater risk of heart and metabolic health problems, such as high blood pressure and cholesterol.

Across all age groups, African-American and Hispanic children had higher rates of overweight and all levels of obesity, while Asian-American children had markedly lower rates. The most prominent trend since 1999 is the increase in all levels of overweight for Hispanic girls, and overweight and Class II obesity (BMI that is at least 120 percent above the 95th percentile for age and sex) among Hispanic males.

"Despite some previous reports, the obesity epidemic has not abated," said senior author Sarah C. Armstrong, M.D., associate professor of pediatrics who is also a member of the DCRI. "This evidence is important in keeping the spotlight shined on programs to support healthy changes. Obesity is one of the most serious health challenges facing children and is a predictor for many other health problems. When we see that leveling off, we can become complacent -- we can't afford to do that."

Skinner said the study has limitations, relying on two-year data that provides snapshots in time across a wide population. But she said the NHANES database is a broader data source than sources for studies that have found declines in obesity rates among smaller or segmented populations. The NHANES 2015-16 data is also the first to include enough data to create a nationally representative sample in Asian-American children, the race or ethnic group in whom rates were actually lowest, at 23.2 percent.

Armstrong, who is also a pediatrician, acknowledges the paper focuses on the problem of obesity rather than solutions, and wanted to encourage families with direct advice.

"Although the latest trends show that we haven't figured out what works as a population, we do know individual changes can support families' health," Armstrong said. "We know families can avoid added sugar in beverages and food, get at least an hour of activity a day, and incorporate vegetables into every meal to improve their health. Even if your child is a picky eater and wants to eat the same vegetable every day, that is still a good choice."

Through projects at Duke Health, DCRI and the Duke Center for Childhood Obesity Research, Armstrong and other Duke scientists are assessing the most effective strategies to reduce obesity in children, including programs that offer at-risk children access to free medical care, partnerships with municipal recreation programs across North Carolina, and even studying children's gut bacteria to determine how the gut microbiome is related to weight.

In addition to Skinner and Armstrong, study authors include Sophie N. Ravanbakht and Eliana M. Perrin of Duke, and Joseph A. Skelton of Wake Forest University.