The five-year study, done by the HCM City Medical Association and its member associations, found the overweight rate increasing from 12.5 percent in 2004 to 18.3 percent in 2009.

The obesity rate was up nearly four-fold from 1.7 percent to 6.2 percent.

The research, the first of its kind in the city, studied anthropometry, environmental, parental, and child factors and child dietary behaviour in 585 junior high school students, Dr Tang Kim Hong of Pham Ngoc Thach Medical University, a member of the research team, said.

Students were asked to wear accelerometers for seven successive days and answer questionnaires to calculate the average daily time for sedentary, moderate and vigorous activities, she said.

The increase in number of overweight and obese children was more among males than females.

The daily time spent on moderate and vigorous physical activities declined from 81 minutes a day to 60 minutes.

Conversely, the time spent on sedentary activities jumped to 210 minutes a day from 120 minutes.

Time spent on physical activity and the body mass index (BMI) – based on height and weight and the most useful measure of overweight and obesity – had a negative association.

Sedentary activities like playing video games, watching television and studying after class were positively associated with BMI.

Having breakfast daily can reduce the risk of becoming overweight or obese.

Overweight and obesity increase the risk of many health problems, including heart disease, diabetes, hypertension, and fatty liver, according to Dr Duong Quang Trung, head of the HCM City Medical Association.

The study emphasised that raising public awareness was an essential measure to help people prevent overweight and obesity by altering factors like diet, physical activities, and habits. /.

Overweight and obesity rates have increased steadily among adolescents in HCM City , and require swift intervention to change dietary intake, physical activities, sedentary behaviour, and lifestyle habits, a study has found.