On a pale morning in a village outside Wuhan, Hubei province, 13-year-old Qian Wei stood in the concrete schoolyard while a health worker wrapped a measuring tape around his waist.

Minutes earlier, the middle school student had been running laps with his classmates and shooting basketballs during recess. Sweat still clung to his temples.

"I exercise every day," he said. But the tape measure suggested something different.

Despite his daily workouts, Qian's waist-to-height ratio placed him in the category of central obesity, a form of abdominal fat linked to elevated risks of diabetes and heart disease later in life.

"I thought only very fat kids had health problems," he said. "I didn't think it could be me."

Unlike general weight gain, central obesity often hides in plain sight. A child can look relatively lean yet carry metabolically dangerous fat deep around the organs.

Qian is far from alone. A nationwide survey of 121,912 rural students aged 8 to 15 — conducted under China's Nutrition Improvement Program for Rural Compulsory Education Students and published in the Chinese Journal of Epidemiology — found that 20.6 percent had elevated waist-to-height ratios.

Using waist-circumference criteria, 17.2 percent met the threshold for central obesity, while another 16.6 percent fell into an elevated normal range.

"Central obesity in rural children is no longer rare," said Zhang Qian, a researcher at the National Institute for Nutrition and Health at the Chinese Center for Disease Control and Prevention. "It deserves urgent attention because it predicts long-term metabolic risk more sensitively than body mass index," she said.

What surprised Zhang's team was not only the prevalence — but the pattern behind it.

Using latent class analysis, a statistical method that identifies hidden subgroups within large populations, the researchers identified five distinct diet and exercise patterns among the students.

Contrary to common assumptions, the highest central-obesity risk did not cluster among the least active children.

Instead, it appeared among children who were physically active but frequently consumed sugar-sweetened beverages and fried foods.

"The frequent beverage and fried-food intake with high activity pattern was positively associated with central obesity risk," Zhang said.

"Exercise does not automatically offset unhealthy dietary choices."

After adjusting for age, sex and region, children who were active but regularly consumed sugary drinks and fried snacks had significantly higher odds of central obesity than active peers who consumed such foods less often.

"This finding is important," Zhang said. "Public perception often assumes that if a child is active, dietary risk becomes less important. Our data do not support that assumption."