Decomposing adult obesity trends in China (1991-2011).

Using data from the China Health and Nutrition Survey, this study analyses two decades (1991-2011) of change in adult obesity in China with a focus on whether rising obesity rates result from all population cohorts becoming more obese across time (intra-cohort change) or recent cohorts being more obese than their earlier counterparts (inter-cohort change or cohort replacement). To do so, we decompose changes in the body mass index (BMI), waist circumference (WC), general obesity and abdominal obesity of adults aged 20+ using both Firebaugh's linear decomposition and Das Gupta's non-linear technique. Our analysis not only reveals significant increases in both general and abdominal obesity (8.1 and 32 percentage points, respectively) in the two decades studied but shows that the rising means in all four measures are mostly attributable to intra-cohort change. In fact, contrary to findings for the U.S., inter-cohort change for the Chinese sample is actually negative, implying that cohort replacement attenuates intra-cohort change over time. Given that intra-cohort change is the central force for the increase in BMI, WC and obesity with individual increases in obesity widely distributed across all cohorts and age groups over time, policy interventions should focus more broadly on all age groups and birth cohorts.