Image copyright Getty Images Image caption A joint UK-US study looked at 4,865 US adults
More than half of young adults aged 20-24 are overweight or obese, according to a major international study.
The research also found that the number of adults aged 18-24 in the UK is nearly triple the number from 30 years ago.
Some 29% of young adults in the UK were overweight or obese, compared with 12% of older adults.
More than 60% of men and 63% of women in the UK were overweight or obese, says the study, which was published in The Lancet.
The scientists collected information from more than 96,000 adults aged between 20 and 64 in the UK, the US, Spain, Germany, Switzerland, Denmark, New Zealand, Austria, Sweden and Australia.
Image copyright Getty Images Image caption The rate of adult obesity in the UK has risen by 57% since 1980
They compared the data to a representative sample of some 3,000 young people in England and found:
Overall, 5.6% of adults aged 20-24 were overweight or obese
13.7% of females and 13.4% of males were overweight or obese
1.8% of younger adults were obese
Among older adults, 11.9% of men and 12.1% of women were obese
The researchers said these findings were “striking and inconsistent with other studies”, which generally showed an increasing prevalence of obesity.
Dr Flavia Pasqualini, who led the study at the Boston University School of Public Health, told the BBC: “It suggests we have a higher-than-expected prevalence of obesity in younger adults.”
“In this study, roughly half of all 20- to 24-year-olds are obese. The trend we saw over the years is clear.
“We now live in an environment which I believe is making our young people obese.”
She said this environment included increased exposure to unhealthy food and beverages, air pollution and, “also importantly, online influences on what they are eating and how much exercise they do.”
Experts said the findings showed “big gaps” in both western countries and could have important implications for health, in both developed and emerging economies.
Dr Brendan McDonagh, director of the Institute of Global Health at the London School of Hygiene and Tropical Medicine, said that the “striking disparity” between western and developing countries could have significant health impacts for many years to come.
Image copyright Getty Images Image caption Obesity carries serious risks for the heart and kidney
He added: “These new figures highlight the dramatic consequences of unhealthy lifestyles for many countries, but also the possibility of lessons for those countries willing to invest in policies that tackle this problem.”
Dr Kathryn Langan, senior research fellow at the Centre for Research on Childhood Obesity at the University of Oxford, told the BBC: “We are talking about a relatively young generation which means this will persist into later life and lead to problems with coronary heart disease, type 2 diabetes and some cancers.”
She said that positive changes needed to be made to healthy living conditions and governments should be prepared to intervene.
“This is an indicator of inequality and inequality of good health in the Western world,” she said.
“If we want to encourage healthier lifestyle then it needs to be shown for everyone to see.
“Unless this environment is changed the problem will continue to develop over time.”
National Obesity Forum’s official spokesperson Siamak Nawaz, who also contributes to International Obesity Task Force, told the BBC: “There is a lot of motivation in our country to eat healthily but there is still very high levels of sugar consumption.”
“It is also very likely that there are areas in the UK where obesity is an issue but nobody knows where and nobody can control that.”
Dr Max Taylor, chair of the British Obesity Therapy Association and the senior lecturer in exercise and sport science at Liverpool John Moores University, told the BBC he was surprised to see “quite a big increase” in adults between the 1980s and 1990s.
“Now, we’ve gone from 12% of adults to 27% of adults, and [this trend] is the same worldwide,” he said.
“We can’t stand still, we have to adapt our lifestyles.”