Obesity is one of the most serious health problems facing modern society and strategies to address this pandemic have so far been ineffective. Although weight loss (WL) is achievable, prevention of weight regain is a major challenge. The overall aim of this thesis was to identify predictors of WL and weight loss maintenance (WLM) to promote better tailored and sustainable interventions. A systematic review evaluated the evidence from 80 studies examining predictors of WL and/or WLM in behavioural and/or dietary WL interventions (with or without exercise) in overweight and obese individuals. Aside from physiological factors such as initial weight loss, a number of personal characteristics broadly conceptualised as reflecting affective, cognitive, behavioural and motivational factors were acknowledged as potential predictors of WL and/or WLM. Affective (e.g. anxiety), behavioural (e.g. eating behaviour, self-monitoring, social support, physical activity, treatment adherence, previous WL attempts) and motivational factors (e.g. self-efficacy) were the strongest predictors identified. Study 1 assessed predictors of WL and WLM in free-living participants (N=71) who received healthy eating advice with (HE+F) or without (HE) advice to increase dietary fibre. Predictors of WL were age, body weight and body image at baseline (affective), fasting plasma leptin and disinhibition (behavioural) with some differences according to diet group. These also predicted WLM at 1 month follow-up. At 12 month follow-up, having a higher body weight at week 12 and greater depression (affective) at follow-up were associated with greater weight regain. Additionally, having stronger beliefs that medical reasons cause obesity (cognitive) and less stressful life events (affective) were associated with better WLM. Study 2 utilised an online survey and cluster analysis to examine affective, cognitive, behavioural and motivational factors in a real world setting with individuals (N=314), who had previously attempted to lose weight using different WL methods. Two distinct clusters were identified: less successful (Cluster 1) and more successful (Cluster 2). Cluster 2 was associated with lower emotional and external eating, lower disinhibition and higher restraint (behavioural), less depression, anxiety and stress (affective), and significantly higher diet satisfaction, eating self-efficacy (motivational) than Cluster 1. Study 3 examined predictors of WL in an NHS delivered 12 week community based weight management programme (N=22). Higher diet satisfaction, an improvement in body image and higher baseline body weight were significant predictors of WL. Based on the evidence presented in this thesis, there are clear personal characteristics which promote and sustain obesity. WL and WLM is clearly not just a problem of appetite control. Affective (stressful life events, body image, diet satisfaction and depression), behavioural (eating behaviour) and motivational factors (self-efficacy and motivation) were the most consistent psychological predictors of WL and/or WLM across all studies. Interventions should therefore target these personal characteristics in order to promote WL and prevent weight regain. The paucity of studies incorporating long-term follow-up shows that further research is needed to examine the role of affect, cognition, behaviour and motivation in the long term. A multidisciplinary approach to tackle obesity, which addresses psychological, social, environmental, and biological factors is essential to ensure comprehensive care, best practice and outcomes.
