Self-Control and Satisfaction with Diet: The Roles of Motivation and Inhibitory Control
The impact of dietary behaviour for health is evident in international data covering the last few decades. Half of the causes of death in high-incomecountries have been related to dietary risks and one analysis has estimated that up to 40% of deaths in high-income countries are directly caused by the long-term consequences of following desire without successful self-control. Overconsumption of highly palatable, unhealthy food, such as refined carbohydrates and processed fats and oils, has been associated with increased Body Mass Index (BMI), increased risk of heart disease, Type II diabetes, certain cancers, central inflammation and neuroinflammation. Despite increased education about dietary consequences, people in the US and Australia report dietary self-control as one of their biggest, but least successful goals for change in their lives, and cite insufficient self-control as the major barrier to successful dietary behavioural change.
This thesis explored dietary self-control and related constructs in order to assess possible interventions for improved dietary outcomes. Relevant literature in the fields of general selfcontrol, nutrition, and dietary behaviour were reviewed in order to establish theoretical foundations and both identify key constructs related to dietary self-control and inform a model of dietary self-control. Grounded in the literature review and results of the initial studies a foundational component of self-control, inhibitory control, was targeted as an intervention for improved dietary outcomes.
A total of five studies were conducted and reported in the current thesis. Study 1 identified high levels of conflict between higher-order dietary goals and tempting food desire as a potential predictor of negative dietary behavioural outcomes. This study created and validated a Dietary Goal-Desire Incongruence scale, which exhibited good psychometric properties and high scores on the scale were associated with maladaptive eating patterns. Study 2 identified the extent and type of motivation, as guided by Self-Determination Theory, as a key construct in improved exertion of self-control for healthy food intake. This study created and validated a Motivation for Dietary Self-control scale, which comprised three subscales (Internal Motivation, External Motivation, and Amotivation) and exhibited good psychometric properties. High total scores were associated with positive dietary behaviour and scores on the three subscales provided a more nuanced pattern of associations, as high levels of internal motivation were associated with more intuitive eating and lower body weight, but high levels of external motivation were associated with more struggle to control eating in the face of tempting desire. Study 3 identified satisfaction as a construct that describes individual evaluation of behaviour against a personal standard and thus could be applied to dietary behaviour. This study created and validated a Satisfaction With Dietary Behaviour scale, which exhibited good psychometric properties. High scores were associated with high positive affect, high body-image satisfaction, high global life satisfaction and low BMI. A stage model linking these three constructs was proposed and results showed that dietary goal-desire incongruence may predict levels of satisfaction with dietary behaviour, and that this path appears to be mediated by motivation for dietary self-control.
Study 4 evaluated three potential models of dietary self-control and showed that a model of serial mediation was the best fit for the data. Serial mediation results suggested that selfcontrol and motivation for dietary self-control significantly mediated the relationship between dietary goal-desire incongruence and satisfaction with diet. This best-fit model showed that a high level of dietary goal-desire incongruence was associated with a decrease in trait selfcontrol, which was then associated with reduced levels of motivation for dietary self-control, which in turn was associated with less satisfaction with dietary behavior. Study 5 evaluated whether an online delivery of Go/No-go inhibitory control training for highly palatable food which was delivered online could result in positive dietary outcomes. The experimental, highly palatable food inhibitory control training group reported intention to eat less unhealthy food than the control group. Counter to expectations, the experimental group exhibited a heightened attention bias to highly palatable food images after the training.
The current research provides three new scales to measure psychological constructs related to dietary self-control and exhibited preliminary validation for these scales. If, as the current thesis suggests, trait self-control and motivation for dietary self-control are mediators between dietary goal-desire incongruence and satisfaction with dietary behaviour, then both self-control and motivation might be promising targets for intervention. The current research supports literature which exhibits positive outcomes from inhibitory control training, but highlights the need for future research into the longevity of training effects and impact on related constructs such as attention bias for food and motivation over multiple training sessions. This thesis contributes to the body of research in self-control, motivation, and dietary behaviour.
Psychological aspects of diet: Development and validation of three measures assessing dietary goal-desire incongruence, motivation, and satisfaction with dietary behavior
Objective: The current research created and validated three new measures of psychological mechanisms associated with dietary behavior: (i) a Dietary Goal-Desire Incongruence scale assessed the degree of conflict between ideal dietary behavior and incongruent tempting desires; (ii) a Motivation for Dietary Self-control scale measured the extent and type of motivation, according to Self-Determination Theory, which may be experienced when trying to control dietary behavior; and (iii) a Satisfaction with Dietary Behavior scale measured successful dietary goal-behavior alignment. Method: A representative sample of Australian adults (N=448, Mage=45.7 years, SD=16.98, 50.2% women) rated items assessing the three target constructs and also completed established scales that measure related and unrelated constructs. Results: Exploratory factor analyses indicated a 1-factor Dietary Goal-Desire Incongruence scale (6 items), 3-factor Motivation for Dietary Self-control scale (11 items), and a 1-factor Satisfaction with Dietary Behavior scale (8 items). Confirmatory factor analyses also supported the model fit of each scale's factor solution. Internal consistency as assessed by Cronbach's alpha (α) was 0.94, 0.78, and 0.94 for the three scales, respectively. A follow-up mediation analysis revealed a stage model of psychological factors related to dietary behavior (as assessed by these three scales) that build on each other. Test-retest reliability was high for each scale (r=.71-.84) and showed sound predictive validity. Conclusion: The Dietary Goal-Desire Incongruence scale, Motivation for Dietary Self-control scale, and Satisfaction with Dietary Behavior scale show good psychometric properties and are brief, easy to administer measures. The utility of the scales can be explored further with other populations and in intervention studies.
Go/no-go for food: Attention bias and intention to eat unhealthy food
Objective: The current research evaluated whether Go/No-go training for highly palatable (HP) food affected attention bias for HP food (an automatic/implicit outcome) and intention to eat unhealthy food (a controlled/explicit outcome). Method: A sample of Australian adults representative for age, gender and Body Mass Index (BMI) (N = 561, Mage = 46.31 years, SD = 16.75, 52.3% women, MBMI = 27.11, SD = 6.34) completed self-report measures of dietary psychological constructs and food image modified Stroop tasks as measures of pre- and post-test attention bias for HP food. After random assignment of participants to two conditions, a Go/No-go intervention was used to train HP food targeted inhibitory control in the experimental group, or general inhibitory control in the control group. All research tasks were delivered online. Results: The experimental, HP food inhibitory control training group reported intention to eat less unhealthy food than the control group, F (1, 637) = 4.81, R² = 0.09, p = .029. Counter to expectations, the experimental group exhibited a heightened attention bias to HP food images after the training, F (1, 637) = 9.48, R² = 0.39, p = .002. Conclusion: Go/No-go training for food may improve both top-down and bottom-up inhibitory control, using both automatic and controlled processes. Further, it may not be effective in lowering attention bias for HP food, but may be effective in lowering unhealthy food intake despite raising attention bias for HP food. Further research that tests these effects using varied reaction time tasks is needed to confirm these results and to explore possible alternative explanations.