Long-Term BMI Trajectories and Category Changes in Older Mexican Adults: A 20-Year Longitudinal Analysis

Background/Objectives: Body mass index (BMI) trajectories and transitions across adulthood are dynamic processes influenced by aging and social- and health-related factors, yet long-term patterns in older adults from middle-income countries remain insufficiently characterized. The objective of this study was to characterize long-term BMI trajectories and transitions, and to identify sociodemographic and clinical factors associated with adverse BMI patterns among Mexican adults aged ≥50 years followed over 20 years. Methods: This study used data from the Mexican Health and Aging Study (ENASEM), a nationally representative longitudinal cohort. Participants aged ≥50 years with repeated BMI measurements across survey waves were included. BMI trajectories and transitions between BMI categories were described, and multinomial regression models were used to examine factors associated with upward transitions and unstable high-BMI patterns. Results: Distinct BMI trajectory patterns were identified over the 20-year follow-up. Participants in stable normal-weight trajectories were younger, more frequently female, and had higher educational attainment and income. In contrast, those with stable overweight/obesity or fluctuating–adverse BMI patterns had higher baseline BMI and a greater prevalence of diabetes, hypertension, and multimorbidity. In multivariable analyses, age contributed to trajectory differences; however, sex, socioeconomic factors, baseline BMI, and chronic conditions remained independently associated with adverse BMI patterns. Conclusions: BMI trajectories in later life are heterogeneous and reflect the combined influence of aging, socioeconomic conditions, and chronic disease burden. Identifying groups at risk of adverse BMI patterns may support the development of targeted interventions to reduce obesity-related health consequences in older adults.