Image copyright Getty Images Image caption The World Health Organisation has classified obesity as a public health emergency
More than half of young adults aged between 18 and 24 are overweight or obese, according to research published in the Lancet.
The study analysed data from more than 1,600 participants in more than 100 countries.
Scientists found that the rate is similar to that in Americans, even though the age group is three years younger.
The WHO considers obesity a global public health emergency.
It says around 600 million people are obese worldwide.
Experts say the study is the first to show that the issue is becoming more common across the world.
Image copyright Getty Images Image caption The study says rates of obesity are similar to that in Americans, even though the age group is three years younger
The findings are based on data from the European Prospective Investigation into Cancer and Nutrition (EPIC), which is sponsored by the European Commission.
The researchers found that while only 40% of men and 33% of women were overweight or obese at age 22, the number of obese adults has risen sharply over the next few decades.
In 1990, 30% of women and 23% of men were overweight or obese, but in 2011, 49% of women and 47% of men were overweight or obese.
In 1990, 20% of women and 16% of men were obese, but this had soared to 37% of women and 26% of men in 2011.
Much higher levels of obesity are found in OECD countries than in the US or the UK.
The evidence is “consistent with a global obesity epidemic”, according to the study’s lead author.
It found that 63% of people in every one of the countries surveyed were either overweight or obese.
The lowest rates were in South Korea (12%), Spain (14%) and Sweden (14%).
The countries with the highest rates were New Zealand (52%), France (53%), Australia (53%) and Canada (56%).
Image copyright Getty Images Image caption The rate of overweight and obesity is increasing in every country surveyed, it found
It was also found that no country had a lower obesity rate than in 1990, except for Denmark (22%).
It said low rates in North America and South America did not reflect the rise in obesity. Instead, it said the rise was due to improvements in diet and not poor lifestyles.
“There has been a significant surge in rates in most wealthy countries, especially in North America, Europe and Australia, with a lower rate in many Oceania and Asian countries,” it said.
Meanwhile, in the UK, a spokeswoman for Public Health England (PHE) said it would be “inappropriate” to comment on the report.
However, she said that PHE had been using the 20% target for childhood obesity, with the aim of bringing this to zero by 2025.
What does the study say?
Image copyright Getty Images Image caption The study found that in every one of the countries surveyed, at least 63% of people were either overweight or obese
The study’s lead author, Marlene Schwartz, said: “If the trajectory continues this way, we are likely to see this increase spread rapidly to Africa.
“The effects of obesity in young adulthood may be costly and disruptive long-term.”
Ms Schwartz said the study was the first to assess obesity prevalence in young adults at a global level.