Worldwide trends in body-mass index by urban and rural place of residence

Abstract

More than one half of the global population lives in urban areas. Urbanisation is often implicated as a driver of the global obesity epidemic. The empirical basis for this claim, however, is often limited data in one or a small number of countries and in limited age and sex groups. My thesis aimed to systematically quantify body-mass index (BMI) trends for children, adolescents and adults in the urban and rural areas of 200 countries and territories. Data on BMI were collated, via the NCD Risk Factor Collaboration (NCD-RisC) network, from population-based surveys that measured height and weight. Data were pooled from 1,154 surveys for the analysis of trends in children and adolescents from 1990 to 2016, and 1,842 surveys for the analysis of trends in adults from 1985 to 2016. I used a Bayesian hierarchical model to estimate urban and rural population mean BMI in each country and year, by sex and age-group. In 2016, mean BMI of children and adolescents living in urban areas was higher than that of their rural peers in almost all countries. The rise in mean BMI from 1990 to 2016 was steeper among urban than among rural boys and girls in all regions, except sub-Saharan Africa and South Asia. By contrast, mean BMI of urban and rural adults in low- and middle-income regions, particularly women, converged from 1985 to 2016, driven by a steeper rise in rural areas. Sub-Saharan Africa was the exception, where urban excess grew for women. In high-income and industrialised regions there was a rural excess in mean BMI for adults in 2016. The rise in mean BMI of rural populations was the largest contributor to the overall rise in BMI in low- and middle-income regions, and the world as a whole. Whereas, the contribution of urbanisation to the rise was at most 17% across all regions. My findings thus challenge the current paradigm that urbanisation is driving the global obesity epidemic and motivate a focus on rural populations if the worldwide BMI rise is to be curtailed. The availability, affordability and accessibility of healthy versus unhealthy foods must be confronted and action taken to create environments that promote healthy diets.