A quarter of West Midlands children will suffer from obesity within four years, the Government will warn tomorrow.
Couch potatoes will suffer from diabetes and heart disease unless they change their lifestyle.
The predicted rise in obesity is revealed in a report commissioned by the Department of Health.
It will be published by Health Minister Caroline Flint, as she launches a campaign encouraging the public to eat healthier food and get more exercise.
The number of boys aged 2-15 suffering from obesity in the West Midlands is expected to rise from 96,182 in 2003 to more than 122,000 in 2010.
This is an increase of more than a quarter and would mean that one in four boys were affected.
Obesity in girls in the same age range in the West Midlands is expected to rise from 98,694 cases in 2003 to 107,000 in 2010, an increase of about nine per cent.
This would mean just under one in four girls were obese.
The report will warn Government cannot tackle the problem alone, and parents must take greater responsibility.
Ms Flint is also expected to launch a campaign encouraging us all to take more exercise.
But she was under fire yesterday from Conservative MP Ann Widdecombe, who accused the Government of wasting money telling people to get fitter - while life-saving drugs were turned down on cost grounds.
She said: "I think there are an awful lot of people who cannot get the drugs that they need on the NHS, who are going to say why on earth should any NHS priority be poured into trying to persuade people to do something which is relatively easy, which is to look after themselves."
It emerged this week that the NHS drugs adviser the National Institute for Health and Clinical Excellence has imposed a threshold of £30,000 for an added year of life provided by a treatment.
Miss Widdecombe, who took part in ITV's Celebrity Fit Club, said: "It's time we were a ll grown up and took responsibility."
But Ms Flint, dubbed Minister for Fitness, insisted reducing obesity levels would lead to NHS savings.
"Obesity costs the NHS £1 billion a year, and the country £7 billion a year. One of the ways we can free up resources is by investing in prevention - that will give us a much better future in terms of determining what other treatments are available."
Her aim was to create "a fitter and more active nation" in the run-up to the 2012 Olympics, she said.
The study, by University College London and the National Centre for Social Research on the Government's behalf, predicted a third of adult men would be obese by 2010.
A spokeswoman for Diabetes UK said: "If obesity rates continue to rise, the number of deaths due to diabetes will increase in line with this.
"The World Health Organisation has already predicted a 25 per cent increase in deaths caused by diabetes over the next decade.
"This is not to mention the blindness, amputations and strokes which the condition can also lead to."