National trends of metabolically healthy and unhealthy obesity before and during the COVID-19 pandemic, 2007 to 2021: A representative serial study in South Korea

Long-term, nationally representative trends in metabolically healthy obesity (MHO) and metabolically unhealthy obesity (MUHO) in South Korea remain limited. Thus, we aimed to analyze the prevalence trends of MHO and MUHO and compare rates before and during the coronavirus disease 2019 (COVID-19) pandemic. We analyzed adults aged ≥ 19 years from the Korea National Health and Nutrition Examination Survey (2007-2021), a nationally representative repeated cross-sectional survey. Obese adults were classified as MHO or MUHO using National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) guidelines. To assess pandemic impact, data were divided into before (2007-2019) and during (2020-2021) the pandemic. National prevalence and temporal changes were estimated using weighted linear and logistic regression with 95% confidence intervals (CIs). A total of 87,625 adults were included (56.51% female). MUHO prevalence consistently exceeded MHO across all years. In 2021, MHO prevalence was 3.63% (95% CI = 2.97-4.28) versus 15.02% (13.05-16.99) for MUHO. Before the pandemic, MHO prevalence increased steadily (β = 0.035 [95% CI = 0.016-0.055]) and continued to rise during the pandemic (β = 0.055 [0.006-0.104]). MUHO prevalence, however, grew more sharply before the pandemic (β = 0.073 [0.036-0.111]) but plateaued during the pandemic (β = 0.061 [-0.031 to 0.153]). This nationwide cross-sectional study highlights distinct trajectories of MHO and MUHO before and during COVID-19. Given the higher and persistent prevalence of MUHO, personalized strategies tailored to metabolic health status are essential in managing obesity in Korea, with important implications for public health policy development.