Thirty years ago international nutritionists were focussing on childhood malnutrition, the 'protein gap' and how to feed the world's burgeoning population, and medical services in the developing world were concentrated on the fight against infectious diseases. Today the World Health Organization (WHO) finds itself needing to deal with the new pandemic of obesity and its accompanying non-communicable diseases (NCDs) while the challenge of childhood malnutrition has far from disappeared, TB and malaria rates are escalating, and the scourge of AIDS has emerged. This has created a 'double burden' of disease that threatens to overwhelm the health services of many resource-poor countries. WHO warns that the greater future burden of obesity and diabetes will affect developing countries, and the projected numbers of new cases of diabetes run into the hundreds of millions within the next 2 decades. The obesity pandemic originated in the US and crossed to Europe and the world's other rich nations before, remarkably, it penetrated even the world's poorest countries especially in their urban areas. The pandemic is transmitted through the vectors of subsidized agriculture and multinational companies providing cheap, highly refined fats, oils, and carbohydrates, labour-saving mechanized devices, affordable motorized transport, and the seductions of sedentary pastimes such as television. This paper briefly reviews these macro-environmental trends as well as considering some of the socio-behavioural influences on weight gain in traditional societies. It concludes, pessimistically, that the pandemic will continue to spread for the foreseeable future, and that, apart from educational campaigns, the governments and health services of poor countries will have few effective public health levers with which they can try to arrest the trend.