Imagine that you saw your last tomato several months ago; apples and pears are a closer memory, plums and strawberries a more distant one. A banana, if you could get hold of such a thing, would probably set you back a week’s wages. In post-war Britain, rationing meant that food was seasonal and in short supply. It was a world without kiwi fruit and Coco Pops but, ironically, it was one where children never had it so good. They were fitter, leaner and generally better nourished than they are now and they would not grow up to be weighed down by the burden of obesity - unlike a quarter of today’s children.

Sixty years on there is seemingly infinite choice in our local supermarkets, from exotic fruit and vegetables to innumerable flours and olive oils. And yet our health is under threat because we are a nation of fatties.

Two years ago, the World Heart Federation warned that obesity will shortly overtake smoking as the world’s biggest killer. According to the federation, 22 million children under the age of five worldwide are now severely overweight. In the United Kingdom, there are 1 million obese under 16s. The United States has the dubious honour of leading the field: the numbers of morbidly obese Americans - those whose body mass is double that of an obese person - has quadrupled in the past 18 years.

In Britain, the chief medical officer’s annual report last year considered the health risks and “potentially catastrophic” effects of obesity. It concluded that it leads to premature death, heart disease, diabetes and cancer, as well as causing reproductive and pre-natal complications. A recent study by Bristol University has even linked childhood obesity to the early onset of puberty and its associated health risks. A woman whose periods began at 11, for example, is 50 per cent more likely to develop breast cancer than one whose periods began at 15.

Treating obesity is expected to cost the National Health Service an extra pound;2.5 billion a year. The epidemic has been attributed to two things: the rise of fast food and a corresponding dip in activity levels. Food Standards Agency research, published last September, concluded that junk-food advertising did influence children’s eating. The Government has asked Ofcom, the television regulator, to review its advertising code.

The alarm bells come as no surprise to Professor Neil Armstrong, director of the children’s health and exercise research centre at Exeter University.

When his first studies were published in 1991, there was a hue and cry about the findings, which showed soaring levels of obesity in children.

“The media went crazy,” Professor Armstrong recalls. “Everyone paid lip service. A minister even came down to visit and then no one did anything at all about it.”

Professor Armstrong’s early research focused on lipid levels in children and identified several factors that were affecting their weight: an unbalanced diet, the downgrading of PE within school, and a reduction in activity levels outside it. “Obesity is multi-faceted. Neither energy intake nor a decrease in sport is sufficient on its own to cause it.”

When he looked at what children actually ate, he was astounded by how few appeared to have breakfast. Many in his research samples did not have a hot meal all day. But all of them ate crisps and drank fizzy drinks.

As a former junior football international, Professor Armstrong is a passionate advocate for sport. Although the Government has poured millions into beefing up sport in the community, there is less commitment to it as part of the crammed school curriculum. This means that many children never acquire the necessary skills to thrive in team games. If they are no good at them, they lose interest and establish an inactive pattern of behaviour.

When this is coupled with a poor diet, it will lead inevitably to weight gain. Seventy per cent of British children give up all sport when they leave school, compared with only 20 per cent of French teenagers.

PPrPofessor Armstrong believes that there is far too great an emphasis on team games at school. “We need to look at the time devoted to PE and balance it between individual and pair activities, such as aerobics and badminton, as well as team sports.”

His views are endorsed by Dr Laurel Edmunds, a former teacher who is now a government adviser on child obesity and a member of the Avon longitudinal study on parents and children. “PE hasn’t changed since I was at school,” she says. “Fat children learn that they are socially unacceptable and yet in PE they have to change in front of each other, which is so humiliating.

They cannot do the tasks as well as kids who are not overweight, and they dislike being active.”

Dr Edmunds believes that if there were a more sympathetic approach to PE, children would find it less alienating. One simple, change would be for schools to abandon mandatory sports kit and let children wear what they feel most comfortable in.

There should also be an increase in physical activity across the whole school, not just during PE. So there could be hopscotches painted on the playground, or simple pieces of equipment that do not require adult supervision. After-school clubs should offer activities such as dance or martial arts to encourage girls who are particularly at risk of dropping out of conventional games.

Dr Edmunds believes that it is pointless trying to force children to change their diets. “Kids get bored of not doing the same things that their friends do, like eating chips and chocolate.” She also feels that drawing attention to their size by singling them out for special treatment will increase feelings of alienation and lower their self-esteem.

There have been moves to establish fat camps or calls for teachers to measure and weigh children at risk. For many working with overweight children, this could have the opposite effect to the one intended and could even encourage bullying.

“It is not about pointing fingers,” Dr Edmunds says. “No one sets out to become overweight, it just happens. Many parents are also unwilling to admit their children have a weight problem.”

Cases of obesity may often be masked by health professionals. Some doctors are reluctant to brand a child as fat; they will tell parents that the child will grow out of it. The difficulty is of course that children grow at different rates and establishing an acceptable heightweight ratio is problematical.

Carol Weir, of the government-backed Community Nutrition Group, visits schools and youth groups to educate young people about eating sensibly. She steers clear of the weight issues and instead sees her role as encouraging healthy eating through cooking and food-based activity sessions.

“We try to give them the building blocks,” she says. “Children are really enthusiastic and we start them off on easy, cheap things like corned beef hash, vegetable lasagne, rice pudding and fruit and custard.” She finds children are particularly motivated if they have grown the food themselves.

All agencies agree that schools have a vital role in establishing healthy lifestyles and eradicating sedentary behaviour, but to do this a headteacher must initiate a whole-school policy that covers not only exercise in school and out of it, but one that also encourages healthy lifestyles at home, particularly among families whose children may be at risk and parents who may be overweight themselves. Trying to cure the problem of obesity at school without treating the cause would be futile, they argue.

For the Health Development Agency, set up by the Government, parents hold the key. Dame Yve Buckland, its chair, says: “Parents can treat their child’s obesity by changing the family’s approach to diet and activity and by avoiding couch potato lifestyles.”

Professor Armstrong wants to see an even greater lead from the Government along the lines of the pound;50 million campaign to encourage parents to walk or cycle with their children to school.

“Schools are working within the terrible constraints of literacy and numeracy targets,” he says. “But there is not much point having very literate cardiac cases. There has to be a balance.”

FIND OUT MORE

International Obesity Task Force

Information on the global epidemic: www.iotf.org.uk British Heart Foundation

Advice for parents and teachers:

www.bhf.org.ukyoungpeople Travelling to School www.dft.gov.uk

Qualifications and Curriculum Authority

Ideas for improving school PE: www.qca.org.ukpess

Food Standards Agency

Join the debate on food advertising:

www.foodstandards.gov.uk