Lifestyle factors and clustered patterns of body shape change in Korean adults: A longitudinal observational study

Background: Obesity is a major health problem driven by lifestyle habits and changes in body composition, particularly increased body fat mass and reduced skeletal muscle mass. Body mass index alone cannot fully characterize adiposity distribution or changes in muscle mass. Body-shape indicators such as waist circumference, waist-to-hip ratio, and waist-to-height ratio predict metabolic and cardiovascular disease risk; however, few studies have assessed longitudinal changes in these measures together with lifestyle factors. In this study, we aimed to identify clusters of body-shape change using 2-year follow-up data from Korean adults and to elucidate the body-composition and lifestyle factors underlying these changes. Methods: K-means cluster analysis was applied to 1,404 participants in the Korean Medicine Daejeon Citizen Cohort using 2-year changes in body mass index, waist circumference, hip circumference, waist-to-hip ratio, waist-to-height ratio, and body weight. Baseline body shape, body composition, and lifestyle indicators were compared across clusters, and multinomial logistic regression was used to identify variables associated with cluster membership. Results: Three clusters were identified: Stable (48.0%), Adiposity-Increasing (31.0%), and Adiposity-Decreasing (21.0%). At baseline, cluster membership was significantly associated with body fat mass. Over follow-up, changes in body fat mass and skeletal muscle mass showed strong associations with cluster assignment. In addition, clinically meaningful worsening in sleep quality (increase of ≥2.5 points in the Pittsburgh Sleep Quality Index) and reduced physical activity (decrease in activity as measured by the Global Physical Activity Questionnaire) were significantly associated with the Adiposity-Increasing cluster. Conclusions: Changes in body composition, especially body fat mass and skeletal muscle mass, were closely associated with body-shape trajectories, while worsening sleep quality and declining physical activity were associated with the Adiposity-Increasing trajectory. These findings support an integrative approach that considers body shape, body composition, and modifiable lifestyle factors when characterizing adiposity-related trajectories and designing tailored lifestyle interventions.