A very modern epidemic is spreading across the globe but this one is not caused by any conventional infectious agent.
It is a global epidemic of obesity and it is spreading at an alarming rate, from the industrialised countries in the west to the developing world where it often sits side by side with malnutrition.
"Globesity" is fast becoming more of a problem than famine and under nutrition, and has now reached a point where it is becoming a serious threat to the health of every nation striving for economic development, scientists said yesterday.
The global "fat epidemic" is no longer the exclusive problem of rich countries and many poorer nations are now facing the double threat of some of its citizens being malnourished while others are seriously overweight, the American Association for the Advancement of Science was told.
A study for the World Health Organisation has found obesity is now estimated to affect 18 per cent of the global population, an increase of 50 per cent over the past seven years, said Marquisa La Velle, a social anthropologist with the University of Rhode Island.
"We assume in developing nations that the problem is one of under nutrition rather than over nutrition," she said.
"What we discovered is that worldwide rates of obesity have increased to the points where many cultures and societies have both under nutrition and over nutrition. This puts a burden on the developing world that it can ill afford and we are looking at a situation in which increased disease and a decline in world health is inevitable.
"We want to alert the science community that people are not immune to this epidemic just because they live in non-industrial or poor populations."
In 1995, there were an estimated 200 million obese adults worldwide. Another 18 million children under-five were classified as overweight.
By 2000, the number of obese adults had increased to more than 300 million and in developing countries it is now estimated that more than 115 million people suffer from obesity-related problems.
The WHO has in the past been reluctant to draw attention to the obesity problem while 815 million people in the world go hungry. But as more information is gathered on this little-understood problem, it has established an International Obesity Taskforce to collect information.
In collaboration with the University of Sydney, the organisation is calculating the worldwide economic impact of overweight and obesity. It is also working with the University of Auckland to analyse the impact that globalisation and economic development are having in promoting the "obesogenic" environment of high-calorie food and a more sedentary lifestyle.
For the first time, the number of overweight individuals in the world rivals those who are underweight, and the developing countries have seen some of the biggest increases.
A 1999 United Nations study identified the growing problem of obesity in all developing regions, even in countries where hunger exists.
In China, the number of overweight people jumped from less than 10 per cent to 15 per cent in just three years. In Brazil and Colombia, the figure hovers around 40 per cent, a level comparable to a number of European countries.
Even sub-Saharan Africa, where most of the world's hungry live, is seeing an increase in obesity, especially among urban women.
In all regions, obesity seems to grow as income increases, scientists have found. The emphasis has been on malnutrition and little is known about the rise of obesity across the continent as a whole. Where research has been done the indications are that obesity is growing fast.
One study found that 44 per cent of black women living in the Cape of South Africa are clinically obese.
Remote rural communities of indigenous people are especially vulnerable to the changes in lifestyle and diet that comes with economic development.
Pacific islanders, for instance, have come to epitomise the dramatic increase in obesity rates that comes with a change to a more westernised way of life, said Stanley Ulijaszek of Oxford University.
"It has been claimed by the International Obesity Taskforce that Pacific islanders are now the most obese populations on earth,' Dr Ulijaszek said.
On some Pacific islands, such as Western Samoa and Tonga, the prevalence of obesity has reached levels of more than 65 per cent for men and 77 per cent for women.
Dr Ulijaszek told the American Association meeting: "It's not just fatness, it's an increase in body size overall and it is not just an issue that is focused on the industrialised societies. These figures [on obesity] are increasing everywhere".
Professor La Velle said famine and infectious diseases have in the past dominated the general health of poorer nations but now obesity is bringing with it a significant rise in diabetes, cancer, heart disease and serious digestive disorders. "This epidemic of obesity has to be seen in a larger context of a generalised, century-long increase in body size and fatness and a decrease in the age of child development – that is child maturation has accelerated while stature and weight has also increased," Professor La Velle said.
In addition to health, the spread of obesity is having an environmental impact as people eat more and expect to enjoy a high-calorie diet rich in animal protein as they become wealthier. As China becomes more prosperous it has moved from an essentially vegetarian diet to one richer in meat.
Professor La Velle said: "Just the increase in leather for increased shoe size would account for a distance of going to the moon and back. So these little increments account for some serious ecological results to do with an increase in the daily intake of calories needed to feed a larger body," she said.
"We can't explain this epidemic from the point of view of a change in genetics or from the point of view of a failure in personal discipline or psychological upbringing.
"We are looking at an epidemic that ... we associate with the adoption of the industrialised way of life. Our diets have changed and our physical activity has declined rapidly.
"Restoring physical activity to our daily lives is critical."