The obesity epidemic is global: 2.1 billion people, or about 29% of the world's population, were either overweight or obese in 2013, and nearly two out of three of the obese live in developing countries, according to a study released Thursday.

The prevalence of overweight and obese people rose by 27.5% for adults and 47.1% for children between 1980 and 2013, according to the study, led by researchers at the Institute for Health Metrics and Evaluation at the University of Washington and published Thursday in the journal the...