Philip James and Neville Rigby say that obesity needs urgent action, while Paul Campos thinks we have much bigger worries on our plate

In the face of robust US government statistics showing that at least 59 million of its adult citizens qualify for the unwelcome soubriquet "obese", it is difficult to give credence to those who pretend that obesity is an exaggerated problem with no real downside for health.

US data from the early 1990s showed that more than 4 per cent of youngsters - almost 1 million teenagers - were affected by the metabolic syndrome, an obesity-related cluster of adverse health factors that indicate real health deterioration and approaching diabetes and heart disease. The number affected will inevitably be much higher a decade later. No one knows how many of the 16 per cent of older children deemed obese by the British Government are affected in this way, but the acceleration in the prevalence of childhood obesity over the past 15 years would suggest that this should be an area for urgent inquiry.

Those who claim that the obesity problem is exaggerated need to come up with good evidence to counter the vast data and agreement internationally that the impact of excess weight gain is far greater than we expected five years ago. Across the world, poor diet and little physical activity, along with smoking, account for about half the world's premature deaths and a substantial proportion of the disabilities and illness that have come to dominate the work of the hospital sector in the developed world and most developing countries. But few countries, if any, are prepared for the impact of the problem.

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Medical concerns are amplified by the suggestion that communities with a long history of malnutrition - with stunted children and adults - are becoming particularly prone to obesity-related disease as they are ushered into environments that substantially reduce the demand for physical work while exposing them to the effects of a sudden increase in fatty and sugar-rich food and drink.

In the first decade of the 20th century, no more than 11 per cent of the average American's dietary intake came from sugar and sweeteners. Now these account for 18 per cent, swollen by a massive surge in the consumption of high fructose corn syrup, which is used in soft drinks as well as foodstuffs. Similarly, Americans enlarged their annual intake of fats and oils from 18.5kg to 32kg per person by the end of the century, and average daily calorie intake is estimated to have increased by 24.5 per cent between 1970 and 2000.

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In addition to bigger helpings distributed on a massive scale by the ubiquitous fast-food emporia, a snacking culture ensures that Americans continue to feed round the clock, like livestock in a fattening shed, forming habits that are hard to break.

International food companies focus on marketing and manipulating the demands of the preschool and school-age child. Western governments add to the burden of the developing world by vastly subsidising farmers to produce the very fats and sugars that we now recognise should be eaten in limited quantity.

As experts have woken up to the scale of the problem, the soft-drink and fast-food manufacturers have noticed a drop in profits. They are also concerned because investment analysts have highlighted junk-food firms as poor investments because any caring government with a commitment to public health will inevitably ask what regulations and restrictions should be put on their activities.

Another worry for junk-food producers is the threat of legal action based on overwhelming evidence of the deliberate manipulation of children's preferences and demands for food. This has prompted McDonald's to introduce salads and companies such as Nestle to rebrand themselves as health and wellbeing companies.

Most food companies now believe they have a problem, but they perceive their biggest challenge to be avoiding the blame. They talk about the importance of individuals getting exercise, dispute the evidence relating to dietary problems or solutions whenever they can find a pliant expert to bolster the status quo, and generally behave in a way reminiscent of the tobacco industry.

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The idea that the food and drinks companies have become suddenly enlightened is equally unlikely. A number of operators in the "big food" and drinks sector of the sugar industry, and for a time the US Government itself, waged a war of attrition with the World Health Organization in the development of its thinking on how to combat obesity through improving diet and increasing physical activity. Now trade associations for both US and European manufacturers want a seat at the table with the WHO in Geneva, presenting themselves as not-for-profit "non-governmental organisations".

However, their representatives still seem to view the obesity epidemic as simply a commercial threat to be contained.

For decades, lobbyists for the food and drink sector have sabotaged any attempt to instil a modern nutritional perspective on government thinking, but the sector now appears to want to change direction and come in from the cold. The problem, however, is when do you begin to trust them? They have effectively manipulated the agenda at presidential and prime ministerial level for years, and ministers to this day in the UK seem terrified of the power and influence of the food industry, which has a turnover second to none. Is public concern at a high enough level to challenge their influence?

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In the UK, the Government fudged its response to the challenge made in the Health Select Committee's report on obesity, which urges strong mandatory measures if the food and drinks industries fail to act. Its Choosing Health white paper emerged to the dismay of anybody concerned with public health, supporting the industry lobby's preferred action - voluntary measures. If nothing effective is done here, the US experience offers the rest of the world an example of what to expect in terms of commercial pressures to increase consumption regardless of the consequences.

Despite 30 years of self-regulated marketing codes, the compelling evidence shows that the American population overall has been systematically overfeeding and now the rest of the world is gradually following in their footsteps, with a further 300-calorie-per-day increase in personal intakes forecast by the Food and Agriculture Organisation. The food and drink industries have so far plumped for more physical activity as the solution to the problem, and by putting their muscle behind sport they seek to add the halo of health promotion to their brands and a shine to their tarnished image.

Trying to shift the onus to the "personal responsibility" of the consumer to choose not to eat what is on offer fails to address the challenge of how to turn down the full-volume marketing for fast food, confectionery and drinks, which we all know we need to consume in smaller quantities.

The challenge for the UK Government after the coming election will be to recognise the concerns of the farming and food industries, but to begin to develop a coherent ten-year strategy that has to produce substantial changes in the way we live. Arguing for a shift in population behaviour should not be derided as a "nanny state" or "social engineering" approach. If we don't do something effective very soon, we won't be able to afford the economic consequences on our healthcare infrastructure.

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Philip James and Neville Rigby are, respectively, chair and director of policy and public affairs of the International Obesity Task Force.