The Aetiology of Food and Drink Preferences, and Relationships with Adiposity
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THE AETIOLOGY OF FOOD AND DRINK PREFERENCES, AND RELATIONSHIPS WITH ADIPOSITY Andrea Dominica Smith A thesis submitted for the degree of Doctor of Philosophy in Epidemiology and Public Health UCL DECLARATION I, Andrea Dominica Smith, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 3 4 ACKNOWLEDGEMENTS I would like to express my immense gratitude and appreciation towards Professor Jane Wardle who was imperative in supporting me in securing the PhD Studentship to join the Health Behaviour Research Centre. It is with great sadness that Jane passed away one year into my PhD, but she was the most supportive and academically forward- thinking source of wisdom and advice during that much too brief period. I will forever be grateful for the initial discussions with Jane that shaped the early ideas for this PhD thesis. A big thank you to my fiercely intelligent supervisors - Dr Clare Llewellyn, Dr Alison Fildes and Dr Lucy Cooke. I will never be able to fully convey how grateful I am for your first-class support and your genuine mentorship. Most importantly, thank you for your generosity – for taking so much of your own time to share your knowledge with me, and for answering all my questions over the past years. It has been an amazing and fulfilling journey, and because of your guidance I have been able to learn more and grow beyond anything I ever could imagine. Thank you for making this process so enjoyable. I would also like to thank Dr Frühling Rijsdijk for her statistical advice, and all the input from the various co-authors and anonymous reviewers on the publications that have fed in to this this PhD. Importantly, I would like to thank all my friends (‘colleagues’) at the BSH. Thank you Moritz for introducing me to the wonders of Mx, for being my travel companion to the most wonderful and weird conferences, and for being such a positive friend. And thank you to especially to Anna, Claire, Monica, Alexia, Gemma and all my other BSH PhD friends, I couldn’t have done it without all your support, hugs, and the countless times that you have made me laugh. I would like to thank Professor Plomin for granting me access to the TEDS twin cohort to collect data for this PhD. I am also grateful to the TEDS twins and the RESIST participants that participated in the research that made this PhD possible. I would like to express my gratitude to the MRC for funding my PhD at the BSH, and for giving me the academic liberty to use these funds to self-direct the scope of the research. Thank you to my parents for their unconditional support, love, and trust in me. I cannot thank you enough for investing in my education from day one, and for encouraging me to be happy by doing whatever I want with my life. And thank you to my brother Christopher, for being an infinite source of advice on everything and anything, especially if it is related to IT issues. A big thank you to my friends, near and far. Special shout out to my Brussel’s ‘crew’, and to Mohsin and Uttara. Even if we are spread across four continents, your messages of support are always much appreciated. Thank you to Stratos and Marilina, your friendship means the world to me. And lastly, thank you to my sister Nici. Without you, I would have never considered embarking on this PhD journey. Thank you for being so self-less and hilarious, and for being there for me at any time of the day. You never fail to push and pull me when necessary, and I cannot thank you enough for being so ever-supportive. 5 6 ABSTRACT Food preferences are important drivers of actual food choice, determining micro- and macronutrient intake; and poor dietary quality increases the risk for nutrition-related disease. Greater liking for sweets, fats and snacks has sometimes been related to higher body fat in childhood, yet the relationship in adults remains unclear. Twin studies are a powerful design to understand the importance of nature and nurture in these behaviours. So far, twin research on food preferences has only used young paediatric or adult populations but the relative importance of genes and the environment in shaping these preferences in early adulthood, a period of increasing independence and autonomous food selection, remains unknown. In addition, drink preferences have received little attention, and there is a need to find out if ‘unhealthy’ preferences are modifiable. This thesis uses data from TEDS, a large population-based cohort of 18-19 year old British twins, to assess the aetiology of food and drink preferences, and to investigate the association of food and drink preferences and adiposity, in late adolescence/early adulthood. Study 1 describes the development of a self-reported food and drink preference questionnaire, confirming that food preferences cluster in six traditional categories: vegetables, fruits, meat/fish, dairy, snacks and starches. Study 2 used the twin design to identify substantial genetic influences on preferences for six identified food categories and seven non-alcoholic drink types. In general, genetic effects were slightly higher for food than drink preferences, but the remaining inter-individual variation for all dietary preferences were influenced by non-shared environmental factors (any influences in the wider environment that make twins less similar despite their shared genes and home environment). Study 3a established that cross-sectional associations between dietary preferences and BMI are limited in this age group; only higher liking for dairy foods and non-nutritive sweetened beverages was positively associated with higher adiposity in older adolescents. Study 3b used a BMI- discordant MZ twin design to show that when genetic and shared-environmental confounding is eliminated, food and drink preferences do not explain adiposity differences in genetically-matched individuals. This design allowed to rule-out genetic or shared environmental factors as contributors to BMI-discordance. Lastly, Study 4 developed and piloted a short three-arm randomized controlled trial comparing two sugar reduction strategies (gradual vs. immediate cessation) to assess the feasibility of sweetness preference modification in relation to hot beverages, i.e. hot tea. Intake of sugar in tea decreased substantially in both sugar reduction conditions, without a loss in overall liking of tea. A better understanding of the aetiology of food and preferences, particularly identifying the importance of the wider environment as a salient shaper of both food and drink preferences, and their relationships with adiposity, has important implications for researchers, policy makers and clinicians. Establishing the feasibility of sweetness preference modification in beverages without loss of liking for the beverage is also important for public health initiatives, suggesting that such preference change is possible and likely sustainable over the long-term. 7 8 Contents DECLARATION............................................................................................................... 3 ACKNOWLEDGEMENTS ............................................................................................... 5 CHAPTER 1:LITERATURE REVIEW ON FOOD AND DRINK PREFERENCES .......... 21 1.1 THE IMPORTANCE OF FOOD AND DRINK PREFERENCES FOR HEALTH AND ENERGY BALANCE ....................... 21 1.1.1 Healthcare and societal costs of poor nutrition .......................................................... 21 1.1.2 Measuring food and drink preferences ....................................................................... 22 1.1.3 Associations of food and drink preferences and adiposity or adiposity ...................... 27 1.1.4 Summary of the findings, strengths and limitations of the current literature on the association between food and drink preferences, and measures of adiposity ..................... 27 1.1.5 Aetiology of food and drink preferences ..................................................................... 36 1.2 SUMMARY OF FOOD AND DRINK PREFERENCE RESEARCH .................................................................... 50 CHAPTER 2: AIMS OF THE THESIS ............................................................................ 53 2.1 KEY OBJECTIVES OF THE THESIS ...................................................................................................... 53 2.2 MY CONTRIBUTIONS TO THE RESEARCH OF THIS THESIS ...................................................................... 55 CHAPTER 3:SAMPLING AND METHODOLOGY ......................................................... 57 3.1 STUDY POPULATION, MEASURES AND METHODOLOGY FOR STUDIES 1, 2, AND 3: THE TWINS EARLY DEVELOPMENT STUDY (TEDS) ............................................................................................................. 57 3.2 THE TWINS EARLY DEVELOPMENT STUDY ....................................................................................... 57 1.1.1 Recruitment process and study structure ................................................................... 57 1.1.2 Representativeness of the TEDS sample ...................................................................... 60 1.1.3 Data Collection ............................................................................................................. 62 3.3 MEASURES ................................................................................................................................ 63 1.1.4 Socio-demographic information .................................................................................