PURPOSE This study examined whether the intensity of participation in the National Fitness Award 100 (NFA100) program is associated with reductions in obesity prevalence and healthcare expenditure in South Korea. A continuoustreatment difference-in-differences (DID) framework with a pseudopanel structure was employed to address the absence of a natural control group. METHODS A pseudopanel defined by sex, age group, and month was constructed using administrative NFA100 records linked with external national statistics on obesity prevalence and healthcare expenditure covering the period from 2022 to 2024. Monthly counts of fitness measurements served as a continuous treatment indicator of participation intensity. To support causal interpretation, stringent diagnostics for the parallel trends assumption were conducted. Average treatment effects were estimated using two-way fixed effects (TWFE) models, and effect heterogeneity was examined through unit-specific interaction terms and a supplementary threecategory age-group specification. RESULTS Greater participation intensity in the NFA100 program was associated with statistically significant reductions in obesity prevalence. The magnitude of these effects was largest among adults in their 20s and 30s, whereas attenuated responses were observed among older adults. Healthcare expenditure also declined, although the estimated effects were modest in size. Substantial heterogeneity across age and sex groups was consistently identified. CONCLUSIONS Higher participation intensity in the NFA100 program contributes to meaningful reductions in obesity prevalence and modest decreases in healthcare expenditure, although program effectiveness varies considerably by age and gender. These findings underscore the importance of tailoring intervention strategies, particularly for older adults, and demonstrate the value of large-scale national health promotion programs.
