A new study has highlighted rising obesity rates among children in rural China.

The study, published in the latest issue of the European Journal of Preventive Cardiology, found children and adolescents in the countryside of Shandong Province to be much fatter in 2014 than they were in 1985.

It was based on a survey tracking nearly 28,000 students from rural schools in Shandong, a predominantly agricultural area, over the 29 years.

The students were aged from seven to 18 when they were surveyed.

Some 17.2 percent of the boys surveyed in 2014 were obese, while the rate was only 0.03 percent in 1985, according to the thesis.

The obesity rate among girls was 9.11 percent in 2014, while in 1985, the percentage was 0.12 percent.

Meanwhile, the proportions of overweight boys and girls climbed to 16.35 percent and 13.91 percent respectively in 2014. In 1985, the proportions were 0.74 percent and 1.45 percent, said Zhang Yingxiu, one of the co-authors of the thesis.

He said the increase was even more apparent among children aged from seven to 12.

The study used a cut-off of Body Mass Index (BMI) -- the ratio of weight-to-height squared -- to define overweight and obesity. A BMI of between 24 and 27.9 was defined as overweight and a BMI at or above 28 was considered obese.

The authors attributed the growing obesity rate to the country's social and economic development, as well as lifestyle changes that had led to excessive energy intake and lack of physical exercise among youngsters.

"Compared with their parents' generation, today's rural children are better fed but spend far less time on physical exercises," said Zhao Jinshan, co-author of the thesis and a nutritionist with the Shandong Provincial Center for Disease Control and Prevention.

The phenomenon is typical among "left-behind children," those who are left in the care of relatives by parents who are busy working in faraway cities.

Cai Shibi, who looks after 20 left-behind children in her village in southwest China's Chongqing Municipality, said at least five of the kids were obese, though their families were not necessarily rich.

One school boy in her care is 110 cm tall but weighs 55 kg. "His parents work far from home and his grandparents spoil him by stuffing him with tasty food," said Cai.

Unlike their parents who ran around having fun and staying fit, many rural children today are couch potatoes, said Zhao.

On the other hand, compared with urbanites, who tend to pay more attention to their dietary balance, most rural residents still prefer meat to vegetables and eat too much salty, oily food, said Zhao. "Dietary habits are a complicated social issue, and rural society needs to enter a certain stage of development for its people to realize the importance of a balanced diet."

Doctors warn that child obesity can lead to hypertension, diabetes and even cardiovascular diseases.