Governments around the world need to make immediate and dramatic policy changes to reverse a pandemic of obesity which could affect an extra 11 million people in the UK over the next 20 years, public health scientists have warned.

The call to act – which includes a prediction that almost half of British men could be clinically obese by 2030 – comes in a series of papers published on Friday in the Lancet medical journal.

The journal begins with a strongly-worded editorial arguing that voluntary food industry codes are ineffective and ministers must intervene more directly.

"Without prevention and control of the risk factors for obesity now, health systems will be overwhelmed to breaking point," the editorial says. "Yet governments' reactions so far are wholly inadequate and rely heavily on self-regulation by the food and beverage industry, and the so-called nudge approach."

There was a particular need for leadership ahead of a UN summit in New York next month on preventing non-communicable diseases such as diabetes and cancer, said one of the authors, Boyd Swinburn, from the centre for obesity prevention at Melbourne's Deakin University.

"Governments have abdicated responsibility. Like a frog sitting in a pan of hot water, we haven't realised what's been happening until it's too late."

The journal carries four new research papers by academics in the UK, US and Australia on what is termed "the global obesity pandemic", charting its causes, implications, likely progression and the ways it could be reversed.

One study, by Claire Wang from Columbia University's school of public health, uses British and American data to track the possible increase in obesity levels if governments continue with current policies.

Based on around 20 years of historic data, the study says that by 2030 as many as 48% of British men could be obese – having a body mass index of more than 30 – as against 26% now. For women, the figure could rise from 26% to up to 43%.

Such a progression is not certain , particularly given slightly more positive data over recent years. But if the historic trend continues into the next two decades the UK could have 26 million obese people, up 11 million on the current figure.

Swinburn's paper comes up with a clear primary culprit: a powerful global food industry "which is producing more processed, affordable, and effectively-marketed food than ever before".

He said an "increased supply of cheap, palatable, energy-dense foods", coupled with better distribution and marketing, had led to "passive overconsumption".

Another study by Steven Gortmaker from Harvard University's school of public health, concludes that the response by governments has been a failure of will which mirrored previous struggles to tackle tobacco consumption.

Ministers knew it made sense to crack down on junk foods but did not have the political appetite to take on such a huge industry.

"I think governments get it, but don't know what to do about it, and don't think it's their responsibility. But it is their responsibility," he said.

His study lists eight cost-effective policies. Topped by a tax on unhealthy food and drink, the rest focus on shielding children from TV advertising or ensuring they exercise more.

The Lancet carries a comment by Sir David King, former chief scientific adviser to the government, carried in large type across the cover: "The conclusions are unambiguous. We need collaborative societal changes in many aspects of our environment to avoid the morbid consequences of overweight and obesity."

A better-informed diet



One of the Lancet papers covers the necessary calculations to lose weight, and brings bad news for those using the long-held rule of thumb that a reduction of 500 calories per day will see a steady weight loss of about 1lb (just under half a kilo) per week.

Kevin Hall from the US's National Institute of Health, said: "This is wrong. It just doesn't happen."

Apart from the many variables of genetics and personal circumstance, this rule of thumb ignores the way the body's metabolism tends to slow down when weight is lost, the reason many diet gains soon tail off.

Hall has devised a far more sophisticated web-based model which allows people to take account of this effect, as well as factors such as exercise, to plot a more likely weight loss progression.

The new simplified rule seems to be that 10 calories fewer per day will also lose you about 1lb – but over three years.

• This article was amended on 26 August 2011. The orginal said the body's metabolism tended to speed up when weight was lost. This has been corrected.