Exploring bidirectional links between body mass index and mental health: The role of intersectionality in the Pro-Saude cohort study

BACKGROUND: The link between body mass index (BMI) and mental health has been investigated. However, longitudinal studies examining the bidirectional associations between BMI and psychological distress are scarce. METHOD: The Pro-Saude study is a prospective cohort study involving non-faculty civil servants from university campuses in Rio de Janeiro, Brazil. Data from baseline (1999, N = 3,668), Wave 2 (2001-2002, N = 2,781), and Wave 3 (2006-2007, N = 2,372) were analysed. Baseline measures included age, sex, race/skin colour, educational attainment, BMI, and psychological distress (assessed using GHQ-12). BMI and psychological distress were reassessed at Waves 2 and 3. Data were collected through self-administered questionnaires and standardised anthropometric procedures conducted at participants' workplaces. Changes in BMI and psychological distress were analysed using latent growth models. Intersectionality was assessed through interaction terms, complemented by age-adjusted linear regression models to examine intersectional effects. Bidirectionality between BMI and psychological distress was evaluated by cross-lagged models. RESULTS: BMI significantly increased over time. Psychological distress predicted BMI but BMI did not predict psychological distress across study waves. Psychological distress and female sex predicted a greater increase in BMI over time. Intersectionality between race/skin colour and educational attainment showed that all subgroups had higher mean BMI than white individuals with tertiary education. Male participants, those with higher BMI, white race/skin colour, and higher educational attainment had lower scores of psychological distress at baseline. CONCLUSION: Prevent weight gain and mental health deterioration among employed adults should be aligned and integrated into workplace health strategies. Interventions targeting specific subgroups, including women, those with brown (pardo) and black skin colour, and lower educational attainment are necessary to reduce inequalities related to BMI.