Psychological mechanisms contributing to alcohol- induced increases in energy intake. Thesis submitted in accordance with the requirements of the University of Liverpool for the degree of Doctor of Philosophy by Thomas Frederick Martin Gough April 2021 i UNIVERSITY OF LIVERPOOL INSTITUTE OF POPULATION HEALTH PSYCHOLOGY (SCIENCE) DECLARATION IN HIGHER DEGREE THESES DECLARATION This thesis is the result of my own work. The material contained in the thesis has not been presented, nor is currently being presented, either wholly or in part for any other degree or qualification. ii Abstract Consumption of alcohol is a significant risk factor for undesirable weight. Previous investigations have demonstrated that acute alcohol consumption reliably increases caloric intake relative to consumption of an alcohol-free comparator, however a complete understanding of the mechanisms contributing to this effect is lacking. Therefore, this thesis investigated the psychological mechanisms underpinning alcohol consumption’s effects on eating behaviour. Specifically, it investigated the role of alcohol-induced changes to cognitive control of eating as well as food reward. The thesis also explored whether alcohol-induced changes to food intake and BMI can be explained by a dual-process account of appetite control - an interaction of top-down and bottom-up processes. Chapter 3 (Studies 1 and 2) investigated whether acute alcohol consumption can impair recall of memories related to a recently consumed meal and whether this affects subsequent food intake. Findings revealed that acute alcohol consumption prior to a lunch meal impaired meal memory recall relative to an alcohol-free drink in Study 2 but not in Study 1. Both studies failed to provide evidence that meal memory recall affects subsequent food intake. Chapter 4 (Studies 3 and 4) investigated whether acute alcohol consumption can enhance food reward, relative to a placebo-alcohol. Study 3 found that an alcohol dose of 0.3 g/kg (grams of alcohol per kilogram of bodyweight) did not enhance food reward (measured using self-report scales and an attentional bias task) or increase food intake. However, Study 4 showed that a dose of 0.6 g/kg, acute alcohol consumption enhanced food reward and food intake relative to the placebo. Contrary to predictions of the dual-process account, the interaction between trait motor impulsivity and change in food-related attentional bias between drink conditions did not significantly predict change in food intake. Finally, Chapter 5 (Study 5) examined whether change in BMI over a 12-month period is predicted by change in drinking behaviour, and whether trait motor impulsivity moderates this effect. Findings did not support these predictions. Overall, the findings of this thesis demonstrate that acute alcohol consumption does affect important cognitive factors implicated in appetite control, however there is no evidence to suggest that this contributes to alcohol-induced increase in food intake. Results also indicate that alcohol-induced enhanced food reward and increases in food intake may be dose-dependent, whereby lower doses of iii alcohol may be insufficient at increasing food intake. The dual-process model of eating behaviour did not appear to explain alcohol-induced change to food intake or BMI in these studies. Further research regarding the importance of cognitive and reward-based mechanisms within the context of alcohol- induced food intake and BMI is now warranted. iv Acknowledgements Thank you to my supervisory team, Dr Charlotte Hardman, Dr Paul Christiansen and Dr Abi Rose for all of your help and support over the past four years. I have gained a wealth of knowledge and experience which I will carry with me throughout my career. A particular thanks to my primary supervisor Dr Charlotte Hardman whose brilliance in research has greatly contributed towards the completion of this thesis. Thank you also to Professor Peter Rogers for providing me with an introduction to the research area, inspiring me to pursue this research further, and for introducing me to Dr Charlotte Hardman. I have also had the privilege of working with brilliant people within the department. Thank you Dr Eric Robinson for providing me the opportunity to work on additional projects during my PhD. Thank you also to the demonstrators who have been a great source of support and help, particularly my office mates, Anna, Rachel and Sarah. Anna, thank you for giving me such a welcoming and friendly introduction to the department. I would also like to thank everyone who participated in my studies. This research would not have been possible without their willingness to consume a substantial amount of vodka during working hours, all in the pursuit of science – a truly selfless act. Lastly, I would like to thank my family for all of their support throughout my PhD and also encouraging me to attend University – Mum, Dad, Hazel, Jamie and many others, thank you. v Contents Chapter 1: General Introduction ......................................................................................................... 1 1.1. The prevalence of obesity ............................................................................................................ 1 1.2. An integrative model of appetite control: combining metabolic, reward and cognitive processes. ............................................................................................................................................ 2 1.2.1. Metabolic control of eating behaviour .................................................................................. 2 1.2.2. Hedonic systems of appetite control and food reward .......................................................... 3 1.2.3. Metabolic control and food reward ....................................................................................... 6 1.2.4. The role of cognitive factors in appetite control ................................................................... 6 1.2.5. A dual-process account of eating behaviour ......................................................................... 7 1.2.6. Attentional Bias .................................................................................................................... 8 1.2.7. Impulsivity, food intake and BMI ....................................................................................... 10 1.2.8. Episodic memories of food and food reward ...................................................................... 12 1.2.9. Summary ............................................................................................................................. 14 1.3. Alcohol Prevalence in the United Kingdom .............................................................................. 14 1.4. Alcohol metabolism and sex differences ................................................................................... 15 1.5. The role of acute alcohol consumption in altering energy intake .............................................. 17 1.5.1. Potential mechanisms producing an acute increase in food intake ..................................... 18 1.6. The effect of alcohol on weight-related measures ..................................................................... 25 1.6.1. Binge drinking and weight gain. ......................................................................................... 27 1.6.2. Alcohol consumption as a predictor of weight gain in University students ........................ 28 1.6.3. Compensatory behaviours of alcohol consumption ............................................................ 29 1.7. Summary and Thesis Aims ........................................................................................................ 30 Chapter 2: General Methods ............................................................................................................. 35 2.1. Questionnaire Measures ............................................................................................................. 35 2.1.1. Alcohol Use Disorders Identification Test .......................................................................... 35 2.1.2. Timeline Followback .......................................................................................................... 35 2.1.3. Dutch Eating Behaviour Questionnaire .............................................................................. 36 2.1.4. Snack Urge Ratings ............................................................................................................. 36 2.1.5. Appetite Ratings .................................................................................................................. 37 2.1.6. Barratt Impulsiveness Scale ................................................................................................ 37 2.1.7. Biphasic alcohol effects scale ............................................................................................. 38 2.1.8. Alcohol Urge Questionnaire ............................................................................................... 38 2.1.9. Subjective Intoxication Scale .............................................................................................. 39 2.1.10. Compensatory Eating and Behaviours in Response to Alcohol Consumption Scale ........ 39 2.1.11. International Physical Activity Questionnaire .................................................................. 40 vi 2.1.12. Food frequency questionnaire: .........................................................................................