Over 40 % of the UK population could be obese "within a generation", experts have warned.
Experts say the estimates are conservative, and could soar even more unless the problem is tackled now.
Children are particularly vulnerable to advertising campaigns by food and drink companies, they say.
Professor Philip James of the International Obesity Task Force, which issued the warning, said: "We are heading for disaster".
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The first step must be to start protecting the health and well being of our young children
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Professor Philip James, International Obesity Task Force
At a meeting of the IOTF, a global think-tank, he called for bold new strategies to be implemented urgently.
Currently one in four men and one in five women are classed as obese in the UK.
The call came a day after the Medical Research Council had urged for action to be taken to tackle child obesity.
Undermining well-being
Professor James said: "The evidence is so compelling that we must now act rapidly and decisively to deal with this epidemic.
"The first step must be to start protecting the health and well being of our young children, who are being damaged because we are not yet willing to provide them with a safe environment where they can experience and learn the value of good food and play.
"Instead their well-being is systematically undermined by the intense marketing and sales of foods and drinks high in fat, sugar and salt.
"But we also need to develop effective strategies that can be made to work throughout society to help everyone address the problem of overweight and obesity."
He said the links between confectionary and soft drink companies and the promotion of physical activity and sport were too close.
Professor James said: "Politicians need to understand that regulation is required and that it is a popular move.
"It is what the majority of parents in every country we work with places as one of their top priorities."
Dr Susan Jebb, of the Medical Research Council, called for schools to be asked about their policies on vending machines and meals as part of the Ofsted inspection process.
She said the watchdog should also look at schools' policies on school meals, tuck shops, out-of-school clubs and vending machines.
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