Urban-rural disparity in body mass index: is dietary knowledge a mechanism? Evidence from the China Health and Nutrition Survey 2004-2015

BACKGROUND: The co-existence of undernutrition and overweight/obesity has been recognised as a severe challenge in China, with substantial urban-rural disparity. We evaluated short- and long-term associations of urban-rural locality on body mass index (BMI) in Chinese adults overall and stratified by sex, focusing on whether dietary knowledge plays a mediating role. METHODS: We used cross-sectional and longitudinal study designs with structural equation modelling based on the 2004 (T1) and 2015 (T2) waves of the China Health and Nutrition Survey. We adjusted the models for covariates and performed sensitivity analyses. RESULTS: We cross-sectionally analysed 8932 (53.1% women) and 11 216 adults (54.3% women) at T1 and T2, respectively, and longitudinally investigated 4073 adults (55.6% women) in both T1 and T2. The estimated average dietary knowledge and mean BMI increased from T1 to T2. At each time point, we found significant indications of direct (e.g. urban-rural locality to BMI, urban-rural locality to dietary knowledge, and dietary knowledge to BMI) and indirect associations (e.g. urban-rural locality to dietary knowledge to BMI) overall and for men and women (except that urban-rural locality to BMI) separately. The long-term association between urban-rural locality and BMI attenuated over time and was not mediated by dietary knowledge change alone. Nevertheless, dietary knowledge interacted with BMI, which acted as a pathway from urban-rural locality to BMI in the long term. CONCLUSIONS: Urban-rural disparity in BMI persists in Chinese adults and is mediated by dietary knowledge. Policy and educational efforts to improve dietary knowledge among rural people may reduce China’s urban-rural disparity in BMI.