Scientists have long recognized the importance of the demographics and epidemiologic transitions in higher income countries. Only recently has it become understood that similar sets of broadly based changes are occurring in lower income countries. What has not been recognized is that concurrent changes in nutrition are also occurring, with equally important implications for resource allocation in many low-income countries. Several major changes seem to be emerging, leading to a marked shift in the structure of diet and the distribution of body composition in many regions of the world: a rapid reduction in fertility and aging of the population, rapid urbanization, the epidemiologic transition, and economic changes affecting populations in different and uneven ways. These changes vary significantly over time. In general, we find that problems of under- and overnutrition often coexist, reflecting the trend in which an increasing proportion of people consume the types of diets associated with a number of chronic diseases. This is occurring more rapidly than previously seen in higher income countries, or even in Japan and Korea. Examples from Thailand, China, and Brazil provide evidence of the changes and trends in dietary intake, physical activity, and body composition patterns.