Forecasts of a huge rise in obesity among children in England have been significantly downgraded following a new analysis of data.
The National Heart Forum found evidence that the rate of increase in childhood obesity may be starting to slow.
Its figures suggest that by 2020 the proportion of boys aged 2-11 who will be overweight or obese will be 30% - not 42% as previously predicted.
For girls of the same age the revised prediction is now 27% - down from 48%.
The revised predictions also indicate a big drop in the number of overweight and obese young people aged 12-19.
They represent the first sign of encouraging news for decades, as obesity rates have been rising in England - as in most developed nations - since the 1970s.
A similar trend has been recorded in several other countries, including the US, France and Denmark.
There are currently 1.5 million children in England who are overweight or obese - leaving them at increased risk of health problems such as type 2 diabetes, cancer and heart disease.
The Department of Health has set a target of reducing the number of overweight and obese children to 2000 levels by 2020.
The National Heart Forum based its latest predictions on data collected for the Health Survey for England between 2000 and 2007.
Previous estimates were based on data collected for the same survey between 1993 and 2004.
The researchers said it was not clear why obesity levels might have levelled off, but said government interventions and media coverage may have played a role.
Work to do
Lead researcher Professor Klim McPherson, said: "These trends present a more positive picture that obesity may be levelling off in children.
"However, prevalence and current trends of excess weight are still unacceptably high and these figures should not be taken as an argument for complacency.
"The government needs to keep up the work they are doing to tackle obesity."
Professor McPherson said obesity rates had to be monitored closely to ensure the predictions were translated into hard fact.
Dr Ian Campbell, medical director of the charity Weight Concern, stressed that while the rate of increase may have dropped, rates of obesity among children were still rising.
He said the government's Change 4 Life campaign - which aims to improve children's diets and boost their level of physical activity - had been well received, and had hopefully made a lasting impact.
But he added: "There is hope for the future but this is no time for complacency."
Tam Fry, from the National Obesity Forum, said: "We will have to wait another two or three years to see if this is a trend or just a blip.
"I am worried about the credit crunch which is already encouraging increased reliance on processed food."
The Minister for Public Health, Gillian Merron, said government initiatives had had a positive impact, along with local work by the NHS and schools.
But she added: "Obesity levels are still too high and we need to keep the momentum going.
"We'll only turn the tide on obesity for good if everyone - government, families and industry - play their part."
And Susan Jebb, head of nutrition at the Medical Research Council, said: "It feels like we are in a different place from just two years ago - and that's justified.
"That's the result of a shift in public awareness and attitude, coupled with some concrete local initiatives to support healthier eating and more physical activity for children.
"This is hopeful but there's no room for complacency."