The World Health Organization says the number of people getting fat is growing at an alarming rate. It estimates that one billion people are overweight and another 300 million in the more extreme condition of obesity. The agency expects the incidence of abnormally high weight will double between 1995 and 2025. Being overweight was once considered an exclusively Western disorder, but it now poses a serious threat to the health of developing nations, too.

Until recently, the main health challenges to developing countries were famine and infectious diseases like AIDS, malaria, and tuberculosis. But a looming specter is now obesity and its associated illnesses, such as heart disease, diabetes, high blood pressure, stroke, and certain forms of cancer. Heaviness is occurring wherever countries are undergoing a shift to urbanization, higher incomes, modern technology and food processing, and more leisure time.

University of Rhode Island anthropologist Marquisa LaVelle told a Boston conference that the greatest increases in average body weight since the early 1950's have been among people in warmer climates.

"Worldwide rates of obesity have increased to the point where many societies have both under-nutrition and over-nutrition," said Ms. LaVelle. "Given the associations of obesity with chronic diseases, with diabetes, as high risk factors for heart disease and cancers of various sorts, this puts a burden on the developing world that they can ill afford."

Researchers at a recent international population meeting in Tours, France gave some examples. They said 25 percent of Indian women under 50 were overweight, as shown in a national survey six years ago. Data from Mexico and Uruguay shows the prevalence of overweight people at about 20 percent.

The situation is worse in cities. Among the Indian women, those at most risk were city dwellers of high income. In South Africa, Marquisa LaVelle found urban Cape Town children taller, but significantly fatter than their rural ethnic counterparts, even in cases where social and economic status were similar. She also discovered that schoolchildren in Melbourne, Australia are heavier for their height than their aboriginal desert counterparts.

But rural areas are not exempt. University of Oxford researcher Stanley Ulijaszek says the weight problem is especially prevalent among South Pacific islanders, where up to two-thirds of men and three-quarters of women are overweight or obese.

"When one thinks of New Guinea, it is to many people as back as the back of beyond [remote] as you can imagine," said Mr. Ulijaszek. "However, if it is permeating the rural communities in these places, it is also permeating Amazonia, it is permeating rural communities across the world, so the epidemic is way beyond simply the industrial nations."

Dzhambulat Khotokhov, right, and Georgy Bibilauri, a Georgian, enjoy a meal, in Tbilisi, Georgia

In the Cook Islands, the island of Rarotonga may be remote in terms of distance from most world capitals, but Mr. Ulijaszek says it looks like a New Zealand suburb now that the effects of industrialization have reached it. As a result, adults in Rarotonga have gained six-centimeters in average height since 1952, but have also gained more weight than is good for their new stature.

"That means with globalization, we have a world food system," he added. "America features strongly in the world food system, and the penetration of the world food system, the "McDonalds-ization," if you will, means that the dietary change can proceed faster in some of these remote places than was ever possible before."

The researchers dismiss the notion that specific genetic traits make some populations more prone to obesity than others. They say the weight gain has occurred too rapidly among too many newly-industrialized cultures to be accounted for by the gene pool. Nor can it be explained by a failure of personal discipline or psychological traits.

Marquisa LaVelle puts the blame on the modern way of living, with its dietary changes and decrease in physical activity. Although she says the impact differs among societies, she believes the solution rests less with dieting than with promoting physical activity.

What is the alternative?

"We are looking at a situation in which increased disease and decline in world health is inevitable," answers Marquisa LaVelle.