Nauru, the tiny island nation northeast of Papua-New Guinea, is facing the worst weight crisis. According to the World Health Organization, almost all of Nauru's adult population is bulging at the waistline.
The situation in the Federated States of Micronesia, Tonga and the Cook Islands is only slightly better.
The WHO says about 90 percent of men and women in these isolated corners of the Pacific are overweight or obese. The region contains eight of the world's fattest nations, while the United States and Kuwait finish up the unenviable list of the 10 most obese.
There are cultural reasons for obesity. Some groups in the South Pacific, especially Polynesians, traditionally equate beauty with physical size.
But a changing diet and a lack of exercise are also key factors in the situation. A growing number of Pacific islanders rely on imported and fatty processed foods, as cheap and easy alternatives to fish, fresh fruit and vegetables.
Louise Hardy, a researcher at the New South Wales Centre for Overweight and Obesity, says the South Pacific diet has been deteriorating for some time.
"We know that their lifestyles have changed significantly over time," Hardy says. "They now have a lot more sugar and a lot more fat introduced into their diets, and probably their traditional way of life has been eroded, and it's more sedentary."
Doctors have warned that obesity can lead to diabetes, heart disease and arthritis. Fat children are increasingly being condemned to a lifetime of ill health and disability.
The problem is truly worldwide. Even in regions with traditionally slim populations, such as East Asia, obesity and its side effects are making their mark.
The World Health Organization has estimated that globally there are 1.6 billion overweight adults. That figure is expected to increase by 40 percent over the next decade.