The aim of this study was to examine in New Zealand mid-life women the relationship between different forms of motivation (as specified by Self-Determination Theory) and change in BMI over 5 years. A secondary aim was to explore potential mediators of this relationship.
Methods: In May 2014, self-administered questionnaires were sent to participants in a nationwide longitudinal study (baseline: 2009, 2-years: 2011, 3-years: 2012). Multiple regression was used to explore the relationship between different forms of motivation at baseline assessed using the Regulation of Eating Behaviour Scale (REBS) and change in BMI over 5-years. Mediation analysis was conducted using the approach of Sobel-Goodman.
Results: At 5-year follow-up, 899 questionnaires were returned (response rate=73%, mean age 50.6 years). Regarding REBS scores at baseline and change in BMI over 5-years, a 12-point higher score for baseline autonomous regulation was associated with a 0.24kg/m2 decrease in BMI over 5-years (95% CI: -0.36, -0.12, P=0.001). In contrast, a 4-point higher baseline amotivation score was associated with a 0.20kg/m2 increase in BMI over 5-years (95% CI: 0.04, 0.40, P=0.020). Potential mediators identified were: variety of vegetables consumed, consumption of high energy density foods and intuitive eating. However, no significant mediators were found for the relationship between baseline REBS scores and change in BMI over 5-years.
Conclusion: This study suggests that autonomy supportive approaches to promoting healthy eating may be helpful in preventing an increase in BMI over time.
Funding source: University of Otago Research Grant