Correction: An earlier version of this article stated that one-third of the world's population is "obese." It should have said "overweight or obese," as those are two distinct categories for medical purposes. Overweight, as defined by the CDC, is anyone with a BMI between 25 and 29.9. Anyone with a BMI over 30 is obese. The article has been updated to clarify that distinction.

According to a comprehensive study, the prevalence of overweight and obese people have been steadily rising throughout the world, to the point where more than one-third of the global population is now overweight or obese. Approximately 2.1 billion people fall into those categories, with 671 million defined as clinically obese.

A new report published in the medical journal The Lancet found that the highest rates of obesity are in the Middle East and North Africa, but the United States is home to 13 percent of the world's obese population, a higher proportion than any other country. Lead author Christopher Murray told CBS News that the findings are "pretty grim," adding that "when we realized that not a single country has had a significant decline in obesity, that tells you how hard a challenge this is."

Data shown for ages 20 and older. Courtesy of The Lancet

To compile the data, researchers combed through surveys, reports and studies from 1980-2013 listing height and weight information for people throughout the world. They found that the percentage of adults with a body-mass index (BMI) of 25 kg/m2 or higher — the threshold for being overweight — rose, for men, from 28.8 in 1980 to 36.9 in 2013, and for women, from 29.8 to 38. They add that for children, the rate of increase is even more frightening: 

Worldwide, prevalence of overweight and obesity combined rose by 27·5% for adults and 47·1% for children between 1980 and 2013. The number of overweight and obese individuals increased from 
857 million in 1980, to 2·1 billion in 2013.

Both the developed and developing world are seeing a rise in a fatter population, but the rates are rising faster in the latter, where access to processed food has been increasing over the past few decades: 

Evidence of a slowdown in the rate of increase of overweight and obesity in the developed world, and suggestions that obesity in more recent birth cohorts is lower than in previous birth cohorts at the same age, provides some hope that the epidemic might have peaked in developed countries and that populations in other countries might not reach the very high rates of more than 40% reported in some developing countries.

Recently, obesity has become more of a global health priority. In June, obesity was recognized as disease by the American Medical Association for the first time, and the World Health Organization has put together a commission tasked with reducing childhood obesity