Experts have called on the government to take urgent action to tackle rising rates of obesity.
One in four British men is obese
They have also urged the food industry and supermarkets to play their part in tackling the problem.
Their comments follow the publication of the Commons health committee report on obesity.
Doctors, patient groups and politicians said the time had now come to act. One in five British women and one in four men are obese.
"Obesity is rapidly becoming one of the greatest threats to child health," said Dr Vivienne Nathanson of the British Medical Association.
"Obesity is not just the responsibility of individuals, or just the Department of Health, but of society as a whole, and a joined-up approach is urgently needed."
Her views were echoed by Dr Ian Campbell, president of the National Obesity Forum.
"The time has come to stop talking and start acting. Both personal and governmental responsibility must be acknowledged and the importance of both dietary restraint and increased activity accepted.
The main recommendations
Traffic light system for labelling food
Health education campaign to highlight the risks
Healthy eating lessons for school-children
Voluntary ban on junk food ads targeting children
Snack vending machines to be removed from schools
National walking strategy
More surgery for obese people on the NHS
"The nation is waiting for clear leadership to bring about joined-up working between agencies in order to stop increasing obesity levels, to encourage and promote healthier lifestyles, and to enable those who wish treatment access to it."
Andrew Prentise, professor of international nutrition at the London School of Hygiene and Tropical Medicine, said: "Many of the most important public health advances in history have been driven by firm but benign government actions.
"I urge the government to take a braver and more determined lead."
The Consumers' Association urged the government to implement the committee's recommendations.
"This stark warning clearly spells out the implications to government if the climate of procrastination and inaction continues," said Sue Davies, its principal policy adviser.
"These recommendations will help tackle many of the barriers that make it so difficult for people to lead healthy lifestyles and must be implemented immediately."
The British Heart Foundation said rising rates of obesity could lead to more deaths from heart disease.
"This report highlights that the UK obesity epidemic is threatening to reverse the current decline in deaths from coronary heart disease," said its spokeswoman Dr Charmaine Griffiths.
"Obesity is a key risk factor for CHD, which kills more than 120,000 people in the UK every year."
Risk to NHS
Niall Dickson, chief executive of the health think tank The King's Fund, warned that extra spending on the NHS could go to waste if the obesity timebomb is ignored.
"This report is extremely important and timely. It demonstrates that the extra funding for the NHS will go to waste if we do not get to grips with the devastating rise in obesity," he said.
"We need government to be brave and intervene to improve the health of the nation, while considering the vital role that individuals, industry, communities and employers have to play."
Manufacturers and the retail sector said they would consider the report carefully.
"The obesity problem is complex and multi-faceted - there are no quick fixes," said Martin Paterson, deputy director general of the Food and Drink Federation.
Politicians attacked the government's record on fighting obesity.
"The government's approach to tackling obesity has been disastrously muddled," said shadow health secretary Tim Yeo.
"We are all tired of hearing about new initiatives, be they committees, obesity summits, consultation papers, 'big conversations' or proposals like a fat tax. After seven years in office, Labour should have some answers."
Liberal Democrat health spokesman Paul Burstow said: "Ministers have been slow to wake up to the scale of the obesity crisis.
"What is required from government is a sense of urgency and determination to implement a strategy to first check and then reverse obesity rates."