Exploring Interactions of Cigarette Smoking and Body Composition with Appetite and Eating Behaviour

Abstract

Appetite regulation and eating behaviour are complex processes influenced by physiological, behavioural, and lifestyle factors. Among physiological drivers, body composition - fat-free mass (FFM) and fat mass (FM) - and resting metabolic rate (RMR) have been identified as important, but evidence is conflicting, and the key modifiers of these relationships remain unclear. Lifestyle factors also play a role: cigarette smoking is linked to lower body weight and weight gain after cessation, yet the mechanisms connecting smoking with appetite and eating behaviours are not well understood. This thesis investigated how body composition (FFM, FM, and RMR), smoking, and physical activity interact to influence appetite, energy intake (EI), and eating behaviour. In Chapter 2, a population-based cross-sectional analysis of over 80,000 UK adults demonstrated that smokers were more likely to engage in real-world eating behaviours consistent with restricted food intake, low diet quality and altered food preference. Chapter 3 extended these findings by examining differences in homeostatic and hedonic aspects of appetite regulation between matched cohorts of smokers and non-smokers. While smokers showed lower cognitive restraint, higher disinhibition, and altered hormonal profiles, these distinctions did not translate into measurable differences in EI. In Chapter 4, deep phenotyping of 130 healthy adults revealed that RMR, rather than FFM, was the strongest predictor of EI, with associations moderated by age, BMI, smoking, and physical activity. FM was linked to higher fasting leptin and postprandial PYY, reduced hunger, lower craving control, and diminished taste sensitivity, with opposite associations for FFM - indicating distinct and often opposing roles of FFM and FM in appetite regulation. In Chapter 5, Bland–Altman analysis demonstrated that field-based methods consistently underestimated EI, physical activity and body composition relative to gold-standard measures, highlighting the importance of methodological rigour in appetite research. Collectively, the studies in this thesis demonstrate that appetite and eating behaviour are shaped by an interplay of both lifestyle and physiological factors. Smoking is associated with altered eating behaviours and traits, while body composition and RMR underpin both homeostatic and hedonic aspects of appetite. Furthermore, multiple demographic and lifestyle factors moderate the latter associations. Methodological biases in measurement may obscure these relationships, reinforcing the need for objective tools. These findings advance understanding of appetite regulation and help to inform strategies to support smoking cessation, weight management, and healthier eating behaviours.