Image copyright AFP/Getty Images Image caption Obesity is more prevalent in boys because they are likely to enjoy more of the family's resources, the study says

Obesity has rapidly increased in young rural Chinese, a study has warned, because of socioeconomic changes.

Researchers found 17% of boys and 9% of girls under the age of 19 were obese in 2014, up from 1% for each in 1985.

The 29-year study, published in the European Journal of Preventive Cardiology, involved nearly 28,000 students in Shandong province.

The study used a stricter cut-off of the Body Mass Index (BMI) than the World Health Organization standard.

"It is the worst explosion of childhood and adolescent obesity that I have ever seen," Joep Perk from the European Society of Cardiology told AFP news agency.

The study said China's rapid socioeconomic and nutritional transition had led to an increase in energy intake and a decrease in physical activity.

The traditional Chinese diet had shifted towards a diet "with high fat, high energy density and low dietary fibre".

Image copyright AFP/Getty Images

'Preference for sons'

The data was taken from six government surveys of rural school children in Shandong aged between seven and 18.

The percentage of overweight children has also grown from 0.7% to 16.4% for boys and from 1.5% to nearly 14% for girls, the study said.

On the reason for the higher prevalence of overweight and obesity in boys, the study says: "The traditional, societal preference for sons, particularly in rural areas, may mean that boys are likely to enjoy more of the family's resources."

The WHO classifies a BMI - the ratio of weight-to-height squared - of 25-29.9 as overweight and from 30 upwards obese.

This study used a lower cut-off of 24-27.9 for overweight and 28 and above for obese.

The researchers recommend that "comprehensive strategies of intervention should include periodic monitoring, education on the pattern of nutrition, physical exercises and healthy dietary behaviour".