The heads of three royal medical colleges issued an unprecedented warning yesterday about the rising epidemic of obesity.
They said doctors were only now beginning to see the terrifying impact of weight problems, which have soared over two decades.
Children as young as six are developing breathing problems, irreversible biological changes and type 2 diabetes, a disease previously only seen in overweight, middle-aged adults.
Obesity rates have doubled among children, trebled in women and quadrupled for men in the past 20 years, according to the expert working party.
The report - published by the Royal College of Physicians, the Royal College of Paediatrics and Child Health and the Faculty of Public Health - painted a stark picture of the problem. They compared their report, called Storing Up Problems, to a landmark study in 1962 by Royal College of Physicians which first outlined the health risks associated with smoking.
The group called for immediate action from "every segment of society" to reduce the rising rates of overweight and obese people in the UK.
Professor Peter Kopelman, chairman of the working party, said: "It is only now that people are really seeing the impact of obesity, and it is terrifying, especially when we look at children. We used to call type 2 diabetes adult-onset because we only saw it in adults in their 40s and 50s who had weight problems. Now clinics are seeing it in children as young as six.
"People in their 20s are developing serious complications as a result of obesity, and these problems are being passed on."
He added: "There is a uniqueness to this report in that we have three royal medical colleges expressing our concern about this. We will have a massive problem to face with the next generation unless we do something now."
One in six children aged six to 15 is now classed as obese, according to the report. Obesity among women has nearly trebled from 8 per cent in 1980 to 23 per cent in 2002. In the same period, the number of obese men has quadrupled from six per cent to 22 per cent.
The experts pointed to studies which showed that the children of overweight parents were twice as likely to become fat themselves compared to those from healthy families.
Dr Penny Gibson, of the Royal College of Paediatrics, said: "Children are suffering physically, psychologically and emotionally from the problems of obesity. Childhood obesity brings with it a hugely increased risk of disease and death in early adulthood."
The joint working party also highlighted evidence that a major cause of the obesity epidemic was the declining rate of exercise. Six out of ten girls and seven out of ten boys fail to do the recommended daily hour of moderate exercise.
Dr Gibson said high-profile child murder cases such as those of the Soham schoolgirls meant that many parents were afraid to let their children go out and take exercise.
"We have got to remove counter-productive messages, like the assumption it is unsafe to go out of the house and play," she said. "Children need designated play areas, streets without cars and the opportunity to exercise and play at school.
"We have got to provide alternatives to watching television as a leisure activity."
The experts also called for better food labelling and a sustained healthy eating campaign to improve the nation's diet. But they stopped short of recommending a ban on advertising of food to children, saying the industry should be encouraged to put its house in order before being threatened with legislation.
Food manufacturers claim they are trying to encourage healthy eating, but can only follow consumer demand.
Martin Paterson, deputy director general of the Food and Drink Federation, said: "Obesity is a very complex problem and we want to work in partnership to tackle the issues. I don't honestly believe that any plan to regulate or prohibit certain foods or advertising will work - that approach is doomed to failure.
"Manufacturers have a role to play, but there is also the issue of individual responsibility. Chocolate and snacks are supposed to be treats, and are marketed like that rather than as something to be eaten in excess. Things like portion size start at home with what people put on their plates."
THE FATTY FACTOR
Adults eat twice as much fatty food as they need
* 23 per cent of women and 22 per cent of men are obese
* 9 per cent of children aged 2 to 4r and 16 per cent of those aged 6 to 15 are classed as obese
* If current trends continue, at least one-third of adults will be obese by 2020
* Treating the effects of obesity costs the NHS £500m a year and the wider economy £1.5bn annually
* Obesity kills 30,000 people a year from conditions such as heart disease and diabetes
* The average adult in England eats more than twice as much saturated fat as they need, but only half the recommended levels of fruit, vegetables and fibre
* 90 per cent of the food advertised during children's television programmes is high in fat, sugar or saltReuse content