Decomposing Trends in Child Obesity

We unravel the absolute level and relative prominence of two demographic processes that are relevant for childhood obesity, and that will ultimately determine the long-term course and pace of change in child obesity rates. We leverage data from the National Health and Nutrition Examination Survey to decompose change in child obesity from 1971 to 2012. We partition change into that attributable to (1) healthier, more nutritionally and economically advantaged cohorts in the population being replaced by cohorts of children who are less advantaged (between-cohort change), and (2) the health habits, nutrition, and social and economic circumstances of all cohorts of children worsening over time (within-cohort change). The rise in obesity among children aged 2 to 19 years is solely due to intracohort change driven by variation in food security composition and in the diet of the population over time. Child obesity in the population rose largely because of individual increases in weight status that are broadly distributed across age and cohort groups. Smaller but significant cohort replacement effects slightly attenuated these intracohort change effects over the study period, leading to a more gradual increase in obesity. Our results provide some reasons for optimism. Given that population estimates of child obesity rose because the typical member of all cohorts became heavier over time at all stages of the early life course, successful policy and health interventions that focus on changing health habits across all ages and generations have the potential to quickly slow or reverse the upward trend in child obesity.