There are now more overweight people in the world than those who have to go hungry, a conference of experts in Australia has heard.

Sedentary lifestyles combined with major shifts in eating habits have contributed towards an obesity epidemic that means some 1.4 billion people worldwide are overweight, while 800 million are under-fed.

To combat this, governments need to adjust domestic policy to allow control over the price of food which could then in turn impact on people’s diets, the annual conference of the International Association of Agricultural Economists has been told.

Barry Popkin, a professor at the University of North Carolina, said that the world’s slide into obesity has happened with dramatic speed.

"The reality is that globally far more obesity than under-nutrition exists," he told the conference on Queensland's Gold Coast.

"Obesity is the norm globally and under-nutrition, while still important in a few countries and in targeted populations in many others, is no longer the dominant disease."

America and Australia have the highest obesity rates in the world – including increasing levels of child obesity - while Japan has one of the lowest.

As the "burden of obesity" shifted from the rich to the poor, Professor Popkin suggested that governments should design economic strategies to influence the national diet.

However, he said, such policies used to control people’s diets would need to be carefully examined.

"A central issue affecting the world’s public health is the need to shift the relative prices of a range of foods to encourage healthier, less energy-dense and more nutrient-dense foods.

"We subsidise some things, we don’t subsidise others. We regulate some items. So, for instance, if we charge money for every calorie of soft drink and fruit drink that was consumed, people would consume less of it.

"If we subsidise fruit and vegetable production, people would consume more of it and we would have a healthier diet."

The conference heard how China was an example of a country’s transition to obesity, with a major shift seen in the diet there from cereals to consumption of more animal products and vegetable oils, along with a decline in physical work, more cars and more television viewing.

Benjamin Senauer, a professor at the University of Minnesota, produced a comparative study of the lifestyles in Japan and America in which he found that the average Japanese household spent almost a quarter of its income on food, while in the US the figure was under 14 per cent.

"Japanese cities are based on efficient public transport – and walking," he said. "The average American commutes to work, drives to the supermarket and does as little walking as possible."

In comparison, the average Japanese man walks four miles a day compared to an American adult averaging between 1,000 and 3,000 steps a day - around one mile.

"For most Americans, getting enough physical activity now required a conscious commitment to exercise and often cost money such as the price of a round of golf or membership of a gym," he told the conference.

"Obesity and overweight bring with them significant risks of chronic disease and premature death and adjusting domestic policy to encourage a less sedentary lifestyle is literally a matter of life and death."

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