Diet and physical activity as possible mediators of the association between educational attainment and body mass index gain among Australian adults

Objectives: To quantify the mediating role of leisure time physical activity (LTPA) and five dietary behaviours on educational differences in 13-year body mass index (BMI) gain across adulthood. Methods: Participants from the Melbourne Collaborative Cohort Study (4791 women; 3103 men) who maintained or gained BMI over 1990–1994 to 2003–2007 and met our inclusion criteria were selected. Education, potential mediators and confounders (age, alcohol, and smoking) were measured at baseline. We conducted sex-specific multiple mediation analyses using MacKinnon’s product of coefficients method. Results: A higher educational attainment was associated with a 0.27 kg m⁻² (95% CI 0.14, 0.39) lesser 13-year BMI gain among women only. We observed significant indirect effects of educational attainment on 13-year BMI gain through LTPA and nutrient-rich foods (each associated with a higher educational attainment and lesser 13-year BMI gain) and diet soft drink (associated with a lower educational attainment and greater 13-year BMI gain), which mediated 10, 15 and 20% of this relationship, respectively (45% in total). Conclusions: Nutrient-rich foods, LTPA and diet soft drink may represent effective public health targets to reduce inequities in excess weight across adulthood.