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The Lancet could not be clearer on the obesity problem: Action is needed - and needed now.

The world-renowned medical journal has devoted a large chunk of this week's issue to the problem.

A series of articles published by researchers from across the world are calling for more to be done. In effect, it is a call to arms for governments and society as a whole.

But how did we get here and what is the solution?

No-one noticed at the time, but the 1960s was probably the turning point for what has become the obesity epidemic.

As the world embraced the era of free love, they also began eating more.

Although in truth, the foundations had probably already been laid during the first half of the 20th Century when people started using cars more and doing less physical jobs.

But this was also accompanied by a decrease in food consumption because of shortages during and after the two world wars.

By the swinging 60s the food chain had recovered and within a decade obesity started rising.

At first it was mainly limited to the rich countries, but today it is sweeping through low and middle-income countries as well.

In fact, it is getting so bad that experts are beginning to question the ability of the individual to take responsibility for their own actions because of factors such as the increasing availability of cheap, fast food.

Harry Rutter, of the National Obesity Observatory, says: "In practice it is easier for people to gain weight than to lose it. Increasing fatness is the result of a normal response, by normal people, to an abnormal situation."

'No country has escaped'

An estimated 500m people across the world are now classed as obese. In the UK, one in four are. Across the Atlantic it is even worse - a third of adults are obese.

Tonga has a particular problem among its female population with seven in 10 women obese.

But even in countries such as Japan and China, which hardly saw any movement in obesity initially, more and more cases are being registered.

"We are seeing an obesity and chronic disease crisis," says Professor Boyd Swinburn, one of the world leading experts in obesity, who is based at Deakin University in Australia. "There is no country that has escaped."

And because obesity is linked to a host of health problems, from diabetes and heart disease to cancer, the burden for health systems is becoming worrying.

In the UK, experts predict obesity levels will nearly double in the next 20 years. That could mean an extra £2bn a year has to be spent by the NHS to cope.

The government - or at least the one in London - is responding by working with industry to encourage healthier lifestyles.

Firms have signed up to a series of pledges to reduce the salt, sugar and fat content of food and to pursue more responsible marketing initiatives.

But for many experts this is not enough. The Lancet researchers have argued tougher action - such as legislation - is needed to tackle the issue.

One of the papers said steps such as a tax on unhealthy food and drinks and traffic light labelling on food would be so beneficial for health that they would save money in the long run.

Some countries - albeit a minority - have started to look at some of these measures.

In September, Hungary will introduce a tax on pre-packaged foods containing high salt and sugar content, such as crisps and chocolates.

Finland and Norway have already taken the step.

The question now is how many more will follow them?