Beijing's children and teens are growing, but not in a healthy way. The obesity rate in the capital ballooned from 14 percent in 2006 to 20 percent in 2013 - significantly higher than the national average - according to the annual Report on Beijing Healthy City Construction, which was released on Monday.

The average rate nation-wide for males and females was 8.6 and 4.1 percent in 2010, the most recent year for which national figures are available, according to the report jointly issued by seven organizations, including the Beijing Health Promotion Commission. Surveys are conducted every five years.

Nearly 19 percent of male students and 11 percent of female students in Beijing were obese in 2010, the report said.

A person who is overweight or obese has an abnormal or excessive fat accumulation that may impair health, according to the World Health Organization.

A person's body mass index-body weight in kilograms divided by the square of the person's height in meters - is a measure commonly used to classify people as overweight or obese. The WHO defines a BMI greater than or equal to 25 as overweight, and a BMI greater than or equal to 30 as obesity.

"Obese youth are more likely to have risks for cardiovascular disease, such as high cholesterol or high blood pressure," said Li Shilian, a physician in the diet and nutrition department at Beijing Children's Hospital.

She added that such individuals are more likely to have pre-diabetes, a condition in which blood glucose levels indicate a high risk for development of diabetes.

"Children and adolescents who are obese are at greater risk for bone and joint problems, sleep apnea and social and psychological problems such as stigmatization and poor self-esteem," Li said.

Worldwide obesity has more than doubled since 1980, according to the WHO, which reports that 42 million children under the age of 5 were overweight or obese in 2013.

The causes of obesity are complex and include genetic, biological, behavioral and cultural factors. Obesity occurs when a person eats more calories than the body burns up, according to the American Academy of Child and Adolescent Psychiatry.

"It can be also related to overeating or to bad dietary habits. For example, children who eat more fat, more salt and less fiber will carry higher risks of getting chronic disease in the future," said Zhang Wei, an official from the Beijing Commission of Education. Lack of daily exercise is also to blame, Zhang said.

Research conducted in 2012 shows that only 30 percent of the city's primary and secondary schools required exercise for at least one hour a day.

In 2013, the commission issued a regulation requiring primary and secondary schools in Beijing to ensure one hour's daily exe example, residents' average daily salt intake dropped from 13.4 to 8.98 grams from 2002 to 2010, and the daily oil intake decreased from 54.6 to 35.15 grams during the period, the report said.

yangwanli@chinadaily.com.cn