Understanding Body Weight Variability in the Context of Weight Management

In the last 5 years, a strong scientific interest in the role of body weight variability (BWV) in health and disease has re-emerged. Due to varied methodologies, the literature is conflicting, yet generally suggests that BWV could be a significant risk factor for disease and mortality. However, the phenomenon remains inadequately measured and poorly understood. This thesis took two discrete but complementary approaches to: (1) understand the aetiology of a weight cycle and (2) understand the measurement of BWV, and its physiological and psychological correlates, with using high-resolution estimates generated through novel technological and statistical procedures. With regards to (1), two studies examined how the rate, amount and composition of weight loss affect subsequent weight regain and appetite. It was found that the amount and rate of weight loss was directly associated with the magnitude of regain, and that greater proportions of fat-free mass loss predicted greater weight regain and appetite in men but not women. With regards to (2), five studies using data collected from the NoHoW weight loss maintenance trial aimed to (i) improve the measurement of BWV and use this to investigate the: (ii) predictability of weight fluctuations; (iii) impact of BWV on health markers; (iv) impact of short-term BWV on long-term weight management and (v) psychological and behavioural causes and consequences of BWV. Briefly, the main findings were that (a) a greater understanding of the measurement (and associated errors) of BWV was achieved; (b) fluctuations in body weight could be predicted by temporal cues (i.e. weekly cycles or holidays); (c) BWV did not affect health markers over 12-months; (d) greater short-term BWV predicted increased weight at 12-18 months and (e) a range of eating behaviour and psychological traits were identified in the aetiology of BWV. To conclude, a full discussion and recommendations for the future study of BWV were provided.