Average body mass index values and prevalence data for overweight show complex patterns varying with sex, age, socioeconomic circumstances, race, geography, and over time. Differences in the predominant lifestyles and developmental status of nations and regions also influence weight patterns.
Estimates of the prevalence of obesity in developed countries vary depending on the definitions used. For example, one recent survey has reported that the prevalence of obesity in the US is 15%, while another survey has found it to be 26%.
It appears that overweight and obesity are becoming more prevalent worldwide, not only in developed nations, but also in the populations of developing countries, possibly as a result of urbanisation, migration, new eating habits and recent affluence. Since modernisation appears to be an inevitable process throughout the world, there is every reason to expect that the epidemic of overweight and obesity will extend globally in the future.