By Ray Dunne
BBC News Online health staff
The government is facing calls to ban junk food ads in an effort to tackle rising rates of obesity. BBC News Online examines if it would work.
Obesity rates are rising fast
The UK, like many other western countries, is facing an obesity timebomb. An estimated one in four men and one in five women are obese.
The number of obese children has doubled over the past 20 years. One in 10 six-year-olds and one in six 15-year-olds are now obese.
Experts have warned that 40% of the population could be obese within a generation unless urgent action is taken.
Being obese increases the risk of developing cancer, diabetes and heart disease. It is responsible for 9,000 premature deaths in the UK each year.
In March, more than 100 of the country's leading health and consumer groups called on the government to ban junk food ads in a bid to diffuse the ticking bomb.
The groups, which included the British Heart Foundation and medical royal colleges, said ads were fuelling rising rates of obesity.
Culture Secretary Tessa Jowell has asked the television regulator Ofcom to investigate.
What are children watching?
Over 70% of all food advertising is on TV
About 40% of ads during children's programmes are for food
Most ads are for confectionary, fast food, pre-sugared breakfast cereals, savoury snacks or soft drinks
Manufacturers spend £285m advertising these foods each year
Source: Food Standards Agency
The Food Standards Agency has also been examining the issue. A report for the agency, published in September, concluded that there was a link between advertising and children's diets.
"We reviewed all of the research that has been carried out over the past 30 years," says Dr Gerard Hastings of the University of Strathclyde and one of the authors.
"Our review found that advertising can have an impact on children's diets.
"Our research is quite robust. It was quite extensive and it went through rigorous peer review."
The FSA has since suggested that there should be restrictions on food ads which target children. However, it has stopped short of calling for an outright ban.
In a consultation document, it says new rules should be introduced to "address the imbalance" between ads for healthy and unhealthy foods.
It suggests this could take the form of limits on ads for "foods, meals or snacks high in salt, sugar or fat".
The FSA said the rules should apply during children's TV slots but says extending them "might also be justified".
About 40% of ads during children's programmes are for food. Most of these are for confectionary, fast food, pre-sugared breakfast cereals, savoury snacks or soft drinks.
Campaigners say the case for an outright ban is clear.
"It's a cast iron case as far as we can see," says Charlie Powell, project officer at Sustain, one of the leading proponents of a ban.
"The food industry spends millions of pounds on these ads because they work. They have been very successful. They influence what children eat."
The facts about obesity in the UK
One in four adult men is obese
One in five adult women is obese
One in 10 six-year-olds and one in six 15-year-olds are now obese
Being obese increases the risk of cancer, diabetes and heart disease
It can reduce lifespan by nine years
Obesity costs the UK economy more than £2bn each year
Experts say 40% of the UK population could be obese in a generation
However, critics say the scientific evidence is not as clear-cut as some campaigners make out.
"I don't think the scientific evidence presented in the Food Standards Agency report supports its conclusion that ads are influencing children's diet," says Dr David Ashton, an epidemiologist at Imperial College London.
"I am not persuaded at all that there is a link. It is convenient to blame large food manufacturers.
"It is much easier than confronting the real issue, which is that decline in physical activity over the last few decades is to blame."
Those opposed to any outright ban on food advertising are quick to point to the experience of Sweden and the Canadian province of Quebec.
Both have strict laws outlawing food ads which target children.
However, Sweden has similar obesity rates to the UK. Quebec has similar obesity rates to the rest of Canada, where there is no such law.
"The bans have had no impact whatsoever on obesity rates," says Dr Ashton.
"Some people might want to say that Sweden and Quebec are not typical of the UK. That may indeed be the case.
"But they are the only live experiments on real people that we have and they have not shown any benefit."
Campaigners dismiss the comparison as simplistic.
"The ban in Sweden was never designed as a measure to tackle children's obesity," says Charlie Powell of Sustain.
"It was brought in in 1991 with the introduction of commercial television.
"Television advertising is just one part. You have to address all commercial activities.
"That is why we want a ban which would end all commercial activities through lots of different media, not just television. Television ads are just one part of it."
The authors of the FSA report shied away from calling for a ban on junk food ads.
"I wouldn't advocate that at the minute," says Dr Hastings.
"The danger of banning ads is that manufacturers will simply turn to other channels."
Dr Hastings believes rather than trying to censor ads, health chiefs should try to harness the power of advertising.
"Marketing has the potential to resolve what is an enormous public health problem," he says. "We should be harnessing it as a way of improving diet."
The government for its part appears to be quite reluctant to ban any form of food advertising.
Tessa Jowell has indicated she prefers a voluntary code for manufacturers and advertisers rather than any law.
"If that doesn't deliver then maybe the government should consider something more draconian," says Dr Hastings.
"But for the moment let this be a warning shot across the bows."