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Thesis Overview and Aims

This thesis reports three experimental chapters in which 8 studies are reported. The literature to date shows that many people with overweight and obesity (Kuchler & Variyam, 2003; Robinson & Oldham, 2016) and many parents (Lundahl et al., 2014;

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Parry et al., 2008) and HCPs (Bramlage et al., 2004; Smith et al., 2008) of individuals with overweight and obesity, underestimate weight status. Based on these studies, it is not clear why weight status is frequently underestimated. The labels of ‘overweight’ and ‘obese’ carry negative connotations due to the high prevalence of weight stigma in the western world (Puhl & Heuer, 2009) and it is possible that the stigma attached to these labels results in avoidance of their use. Alternatively, it could be that under-detection of overweight and obesity is due to a genuine inability to accurately visually identify different weight statuses. Increases in the global prevalence of overweight and obesity may have created an upward shift in what is visually perceived as being a ‘normal’ weight. If larger body sizes are now perceived as being normal this may explain underestimation of overweight and obesity. The first two experimental chapters of this thesis examine visual under-detection of overweight and obesity and test a novel, norm based theory to explain the visual underestimation of overweight and obesity.

Chapter 2 reports three studies which aimed to examine whether the general public were able to accurately visually categorise male weight status and whether exposure to heavier body weights made visual underestimation of overweight and obesity more likely. In Study 1, a large sample of the UK general public were asked to objectively judge the weight status of photographed males in a confidential online survey. Thus, there was no apparent motive for participants to deliberately

underestimate the weight status of individuals they did not know and would not meet. In Studies 2 and 3 I wanted to examine the idea that underestimation of overweight and obesity may be caused by increased visual exposure to heavier body weights. Study 2

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aimed to examine whether individuals with more overweight social contacts were more likely to visually underestimate overweight and obesity. Participants indicated whether their peers were on average slimmer or larger than a male with overweight and I examined whether individuals with heavier peers were more likely to visually underestimate overweight and obesity. The effect of visual exposure to heavier body weights on weight perception was then tested experimentally in Study 3. Participants were exposed to photographed males with either normal weight or obese BMIs or control images of neutral objects before being asked to estimate the weight status of an individual with overweight.

Chapter 3 reports 3 studies which build on the findings of Chapter 2 and aimed to provide a comprehensive test of a norm based theory of the visual underestimation of overweight and obesity. In Chapter 2 I only examined visual perception of male overweight and obesity. Therefore, in Study 1 of Chapter 3 participants were asked to visually judge the weight status of photographed men and women with normal weight, overweight and obese BMIs. Study 2 aimed to comprehensively test whether body size norms were associated with underestimation of overweight. Participants were asked to make judgements about ‘normal’ body sizes and visually estimated the weight status of photographed men and women with overweight. I examined whether those who

perceived larger bodies as being normal were more likely to underestimate overweight. In Study 3 I brought Studies 1, 2 and 3 from Chapter 2 and Studies 1 and 2 from Chapter 3 together. Participants were exposed to either men or women with normal weight or obese BMIs. I examined whether exposure to heavier body weights resulted

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in participants reporting larger body size norms and whether this in turn led to greater visual underestimation of male and female overweight.

Based on the literature to date it is not clear whether underestimation of overweight and obesity is helpful or harmful in terms of promoting better weight

management. Some research suggests that accurately identifying overweight and obesity is important as self-identification of overweight may lead to greater motivation to change behaviour and lose weight (Duncan et al., 2011; Kuchler & Variyam, 2003). However, an alternative body of research suggests that identifying as overweight or obese may actually be harmful and could lead to maladaptive eating behaviours and weight gain over time (Duong & Roberts, 2014; Robinson et al., 2015). This link between feeling overweight and weight gain occurs independently of actual BMI (Duong & Roberts, 2014; Robinson et al., 2015), which could suggest that the

psychosocial experience of identifying as overweight may contribute to overeating and weight gain. However, experimental work examining the effect of the psychosocial experience of overweight on eating behaviour is currently limited. The third of my experimental chapters aims to experimentally explore the effect that feeling overweight has on eating behaviour. Furthermore, Chapter 4 aims to examine mechanisms which may explain why feeling overweight could affect eating behaviour.

In Study 1 of Chapter 4, women wore a body suit that made them appear obese or control clothing, before participating in a bogus taste test in which they were asked to taste and rate snack foods. I examined whether wearing the obese body suit impacted on snack food consumption. Specifically, whether women who wore the obese body suit

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ate more than women wearing the control clothing. Study 1 also explored multiple explanations for why the psychosocial experience of feeling overweight could impact on snack food consumption. The hypothesis that feeling overweight would result in increased consumption as a result of greater concern over negative appraisal was experimentally examined by manipulating whether participants were exposed to others whilst wearing the body suit. I also examined whether changes in positive and negative affect may explain changes in eating behaviour as a result of ‘feeling overweight’. Finally, I examined whether women who wore the obese body suit were more likely to implicitly identify themselves as being overweight and whether this psychological process mediated the effect of the obese body suit on snack food consumption. Study 2 of Chapter 4 built on Study 1 by examining whether the effect of feeling overweight on snack food consumption was moderated by gender. Men and women wore either the obese body suit or control clothing in a public setting before participating in the same bogus taste test as in Study 1. As well as examining whether the effect of the body suit on consumption was moderated by gender, Study 2 again tried to pin point the

mechanisms underlying the effect of feeling overweight on snack food consumption. I examined whether wearing the obese body suit impacted on two measures of self- control as a result of anticipated stigma. Furthermore, I examined whether wearing the obese body suit led to decreases in self-esteem or increased concerns about physical appearance and whether either of these factors mediated the effect of the obese body suit on consumption. Finally, in Chapter 4 a meta-analysis is reported which synthesises

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the data from four studies that have examined the effect of wearing an obese body suit on snack food consumption.

In summary, across 6 studies Chapters 2 and 3 of this thesis aim to examine visual underestimation of weight status and test a novel, visual norm based explanation for the widespread under-detection of overweight and obesity in men and women. The aim of Chapter 4 is to test whether the psychosocial experience of feeling overweight leads to increased snack food consumption in men and women and to evaluate the role of potential mechanisms in explaining why perceived overweight can result in

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