This paper examines the speed of change in diet, activity, and obesity in the developing world, and notes potential exacerbating biological relationships that contribute to differences in the rates of change. The focus is on lower- and middle-income countries of Asia, Africa, the Middle East, and Latin America. These dietary, physical activity, and body composition changes are occurring at great speed and at earlier stages of these countries' economic and social development. There are some unique issues that relate to body composition and potential genetic factors that are also explored, including potential differences in body mass index (BMI)--disease relationships and added risks posed by high levels of poor fetal and infant growth patterns. In addition there is an important dynamic occurring--the shift in the burden of poor diets, inactivity and obesity from the rich to the poor. The developing world needs to give far greater emphasis to addressing the prevention of the adverse health consequences of this shift to the nutrition transition stage of the degenerative diseases.