Elementary and middle school students get ready for a 10-day training camp to lose weight in Jinan, Shandong province. About 500 participated.[Photo provided To China Daily]

More than two billion children and adults, or one third of the world's population, are now overweight or obese, according to a new study released Monday.

The study, in which researchers assembled data from 195 countries and territories to model trends in overweight or obese and related health problems and deaths, showed that the prevalence of obesity has doubled since 1980 in more than 70 countries and has continuously increased in most other nations.

Of the four million deaths attributed to excess body weight in 2015, nearly 40 percent occurred among people whose body mass index (BMI) fell below the threshold considered "obese."

The findings represent "a growing and disturbing global public health crisis," according to the authors of the paper published in The New England Journal of Medicine.

The results of the study are based on data from the most recent Global Burden of Disease study, a systematic, scientific effort to quantify the magnitude of health loss from all major diseases, injuries, and risk factors by age, sex, and population.

It found excess weight affected 2.2 billion children and adults worldwide in 2015, including nearly 108 million children and more than 600 million adults with BMI exceeding 30, the threshold for obesity.

Although the prevalence of obesity among children has been lower than among adults, the rate of increase in childhood obesity in many countries was greater than that of adults, it said.

BMI is calculated as weight in kilograms divided by height in meters squared. A BMI between 19 and 24 is considered normal and healthy, while a BMI between 25 and 29 is overweight, and a BMI over 30 is considered obese.

Among the 20 most populous countries, the highest level of obesity among children and young adults was in the United States at nearly 13 percent; Egypt topped the list for adult obesity at about 35 percent. Lowest rates were in

Bangladesh and Vietnam, respectively, at one percent.

China with 15.3 million and India with 14.4 million had the highest numbers of obese children; the United States with 79.4 million and China with 57.3 million had the highest numbers of obese adults in 2015.

"People who shrug off weight gain do so at their own risk -- risk of cardiovascular disease, diabetes, cancer, and other life-threatening conditions," study author Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington, said in a statement.