The analysis in the Lancet is the largest of its kind and looks at obesity trends in over 200 countries.
In the UK, one in every 10 young people aged five to 19, is obese.
Obese children are likely to become obese adults, putting them at risk of serious health problems, say experts.
The Lancet analysis, released on World Obesity Day, comes as researchers from the World Obesity Federation warn that the global cost of treating ill health caused by obesity will exceed £920bn every year from 2025.
Obese the new 'norm'
