Chronic non-communicable diseases, such as obesity, diabetes, cancer, and cardiovascular disease pose a significant global burden in term of disability, mortality, and associated economic costs. Chapter 1 reviews evidence for link between diet and health, and argues that ensuring that individuals are eating healthfully (i.e., a higher proportion of foods that are conductive to health and a low proportion of foods that are not conductive to health) is a key strategy to improve public health. Recent government guidelines in the United Kingdom (where the sample population for the studies in this thesis is drawn from) are outlined and it is highlighted that current consumption does not match recommendations for health, and therefore, it is necessary to build more effective interventions to reverse consumption trends.
Chapter 2 provides a brief background and evaluation of the use of theoretical models in describing, predicting and explaining dietary behaviour. In light of the limitations of traditional social cognitive models, Temporal Self-Regulation Theory (TST) is discussed as a theoretically promising alterative, but gaps in the evidence base are identified.
Chapter 3 presents the first study in the thesis. It is composed of a pilot study and prospective survey. The pilot study investigated the expected outcomes of fruit and vegetable (F&V) consumption and unhealthy snacking for the target population and explores their perceptions of cues in the environment that increase or decrease the likelihood of enacting the target behaviour. The results of this pilot study were used to develop measures used in the main study. Study 1 found that the constructs identified by TST significantly predicted eating intentions and behaviour for consuming healthy and unhealthy foods, however, contrary to expectations, the capacity to self-regulate (operationalised by the Brief Self-Control Scale) did not significantly explain variance in either behaviour. This suggested that TST may be a useful framework for understanding the determinants of healthful eating; however, further research is required to extend the findings using a different measure of self-regulatory capacity.
Chapter 4 presents a study that aimed to investigate how different measures of self-regulatory capacity relate to eating behaviour. The chapter begins with a discussion of the different ways in which researchers have conceptualised and measured self-regulatory capacity as level of self-control or specific executive functions. Study 2 tested how well unhealthy eating (which can be thought of as a self-regulation dilemma) could be predicted by multiple measures of self-regulatory capacity; conceptualised as a global ability or specific cognitive functions, and assessed via self-report or objective methods. In addition, self-report and objective measures of chocolate consumption were administered in order to explore if measurement congruence influenced the statistical strength of the relationship between self-regulatory capacity and unhealthy eating. None of the measures of self-control were significantly correlated to measures of food consumed for the sample as a whole. For individuals with high intentions to avoid high calorie snacks, scores on an objective measure of switching (a dimension of excutitive functioning) were correlated with unhealthy eating such that those who were less flexible ate less chocolate in the past week. Overall, these findings were contrary to predictions based on TST and theories of self-regulation, which propose that the capacity self-regulate is important for avoiding unhealthy behaviour.
After conducting Study 2, it was concluded that further research was necessary to synthesise current research findings and to (i) establish the strength of the relationship between self-regulatory capacity and healthful eating, and (ii) identify moderators of this relationship. Chapter 5 presents a systematic review and meta-analysis of the correlation between measures of self-regulatory capacity (which were broadened from self-control, executive function and delay of gratification, to include impulsivity and conscientiousness) and food consumption. Data from 120 studies and over 77,000 participants showed a significant, small, positive correlation indicating that those with better capacity to self-regulate ate more healthfully (i.e., a higher quantity of healthy foods and/or lower quantity of unhealthy foods). The aspect of self-regulatory capacity moderated the relationship between self-regulatory capacity and food consumption, as did the type of measure (i.e., self-report or objective) of self-regulatory capacity.
The final chapter (6) reviews the main findings in this thesis, including that behaviour appears to be directed by both automatic and reflective processes in line with TST and dual process theories. However, the contribution of these processes is not consistent across different eating behaviours and contexts, and these variations warrant further investigation. Overall, future directions for research and interventions are suggested to enable a better understanding of the determinants of food consumption patterns and develop interventions to reverse current unhealthy eating trends.
