Motivation, Self-determination and Five-year Weight Change
Background: Since traditional weight management approaches have been reported to have poor long terms success, prevention of weight gain has been identified as an important goal. Mid-life, in particular for women, has been recognised as an important life stage for weight gain prevention. Intuitive eating and quality of motivation are two factors that may play a role in the prevention of weight gain. Objectives: To determine, in a population of New Zealand mid-life women: 1. The degree of stability of regulation of eating behaviour scale (REBS) scores over 5 years (ie a measure of quality of motivation derived from Self-Determination Theory). 2. The relationship between REBS and change in Body Mass Index (BMI) over 5 years. 3. Mediators of any relationship between REBS and change in BMI over 5 years, with hypothesized mediators being intuitive eating and other food intake behaviours. Methods: In May 2014, self-administered questionnaires were sent to the cohort of women who had previously participated in the ‘Weight Control Practices and Regulation of Eating Behaviours in New Zealand Women’ longitudinal study. The 5-year followup questionnaire included measures of regulation of eating behaviours, intuitive eating and dietary intake, as well as self-reported weight. These measures and self reported height were also included in most, if not all, of the previous questionnaires (baseline=2009, 2-years=2011, 3-years=2012). Logistic regression was used to determine the odds of having a stable REBS score over 5 years for women in each BMI category. Multiple regression was used to determine if a relationship was present between baseline REBS and change in BMI over 5-years. Once established, mediation analysis was conducted to identify potential mediators of this relationship. Results: At 5-years, questionnaires were returned by 899 women (response rate=73%, mean age=50.6 years). The majority of participants had stable REBS scores at 5-years compared with baseline. Stability was defined as a change of less than 4-points within a subscale, except for autonomous regulation, for which stability was defined as a change of less than 12-points. Compared to women with a healthy BMI, obese women were 38% (P=0.004) more likely to have a decrease of 12-points or more in their autonomous regulation score and 36% (P=0.001) more likely to have an increase of 4-points or more in their amotivation score. When looking at the relationship between specific REBS subscales at baseline and change in BMI over 5-years, a 12-point higher score in autonomous regulation was associated with a 0.20kg/m2 decrease in BMI over 5-years (95% CI: -0.336, -0.057, P=0.006) and a 4-point higher score in amotivation at baseline was associated with a 0.19kg/m2 increase in BMI over 5-years (95% CI: 0.010, 0.361, P=0.039). The relationship between autonomous regulation and change in BMI over 5-years was partially explained by the following mediators: consumption of a greater variety of vegetables, lower consumption of high energy density foods and eating intuitively. For the relationship between amotivation and change in BMI over 5-years, mediators that partially explained the relationship were: consumption of fewer types of vegetables, higher consumption of high energy density foods and less intuitive eating. Conclusion: This study suggests maximising women’s autonomous regulation of eating behaviours and minimising amotivation for eating behaviours may help prevent an increase in BMI over time.
Advisor: Horwath, Caroline
Degree Name: Master of Science
Degree Discipline: Human Nutrition
Publisher: University of Otago
Keywords: New Zealand; Eating regulation; Weight change; Mid-life; Women
Research Type: Thesis