The report said 16% of US children and teenagers were obese.
Child obesity rates may have reached a plateau in the US after decades of almost continuous rises, a report says.
An analysis of data from 1999 to 2006 by the US government's Centers for Disease Control and Prevention showed obesity rates stable at 16%.
Public health experts remained cautious about the findings and were unable to pinpoint the reasons for them.
But the results have prompted speculation that a similar trend could emerge in the UK.
The US data was based on a survey of over 8,000 children aged between two and 19.
The Journal of the American Medical Association report comes after the obesity rate has been rising for three decades.
One theory for the trend is that public health campaigns aimed at raising awareness of the problem and improving school meals have had a positive impact.
Another suggestion is that there has been a natural levelling off related to the proportion of the population who are susceptible to obesity.
Cynthia Ogden, the lead author of the report and an epidemiologist for the National Center for Health Statistics, added: "It doesn't mean we've solved it, but maybe there is some opportunity for some optimism here."
But despite the caution, experts are hopeful a similar pattern could materialise in the UK.
Dr Ian Campbell, medical director of Weight Concern, said: "It might be a natural trend. The British government has forecast that 50% of us will become obese, but I've never thought obesity would rise exponentially.
"A large part of what makes us prone to being overweight is genetic make-up."
Dr Campbell added: "We're about five years behind the US. It would be great if we followed them and obesity did level out. This will be helped by government programmes to reduce it.
"There's a lot lined up in the next 12 months that is bound to influence people to lead a healthier lifestyle."