Temporal Patterns and Cross-Sectional Correlates of BMI-Defined Weight Status Among Mexican Adults Aged 50 Years and Older

Background: Fluctuations in body mass index (BMI) have been associated with frailty, functional decline, and increased morbidity and mortality. However, evidence on the longitudinal evolution of weight status in aging populations remains limited. This study aimed to characterize population-level patterns and individual longitudinal fluctuations in BMI-defined weight status among Mexican adults aged 50 years and older between 2001 and 2021 and to examine factors associated with BMI categories across survey waves. Methods: This observational study was based on a secondary analysis of data from the Mexican Health and Aging Study (ENASEM). Data from the 2001, 2003, 2012, 2015, 2018, and 2021 survey waves were analyzed. Weight status was classified according to BMI as underweight, normal weight, overweight, or obesity. Differences in weight status were assessed using χ2 tests adjusted for the complex survey design. Results: Most participants remained in the same BMI category during follow-up; however, relevant transitions between categories were observed, particularly between 2001–2003 and 2018–2021. The longitudinal analysis showed that 32% to 38% of individuals changed BMI category between periods. Obesity showed high persistence, whereas overweight showed greater variability. Wave-specific cross-sectional analyses showed that older age was consistently associated with lower BMI-category position, whereas several socioeconomic and clinical characteristics also exhibited cross-sectional associations with BMI category across survey waves. Conclusions: Although the population-level BMI distribution showed relative stability, relevant individual-level fluctuations were observed. Age and several sociodemographic characteristics were associated with differences in weight status patterns.