"I cannot keep the weight off": Understanding the role of social identity in weight loss maintenance

肥胖（身体质量指数（BMI） bbb30kg -2）是导致过早死亡的主要原因(1)，也是一个紧迫的公共卫生重点。肥胖不分青红皂白，但尤其影响社会弱势群体，是2型糖尿病和冠心病等疾病的主要危险因素(2)。肥胖与焦虑、抑郁和孤独有因果关系，部分原因是由于反复暴露于体重耻辱(3)。严重肥胖（体重指数为40公斤/ 2）的人对健康的不良影响更为明显，寿命缩短10年(4)，并与体重耻辱经历增加(5)有关。然而，尽管严重肥胖对健康的影响加剧，并加速了严重肥胖的流行(6)，但对严重肥胖人群的研究仍然不足。经济上，到2050年，肥胖每年将花费英国国民保健服务体系97亿英镑(7)，尽管其患病率相对较小，但严重肥胖占其中的24-35% (6)；部分原因是更密集的治疗，包括手术、药物和行为干预(8)。简而言之，肥胖（以及越来越严重的肥胖）是常见的，改变着生活，限制着生活。针对肥胖和严重肥胖人群的NHS体重管理专业项目越来越多地采用小组形式(9)。以群体为基础的行为干预在中短期内有效地支持行为改变和体重减轻（10），减少合并症风险并改善生活质量（11）。然而，几乎80%的计划参与者在3-5年内恢复了体重（12）。在线论坛用户（13）报告了减肥成功，但在维持体重（饮食和体育活动）行为方面遇到了困难。由于持续的治疗需求，由此产生的“体重循环”对健康和NHS来说代价高昂。因此，需要研究如何将这些专家规划的有效性扩展到治疗环境之外。目前的博士学位旨在通过跨学科的方法来解决这一差距。健康的社会认同方法（14）为本博士提供了理论框架，并考虑了社会群体成员共享社会认同（SSI）对健康的影响。这种方法强烈地将社会认同与一系列健康结果联系在一起。在基于群体的肥胖管理的背景下，它提供了对群体治疗效果的理解，并概述了SSI如何作为支持健康行为决策和相关动机和能力的关键资源（15）。重要的是，群体过程已成为新的群体干预的焦点。支持体重行为管理（16,17）和肥胖相关的认知和情绪压力源，包括体重耻辱、低自尊和孤独（18），这些压力源会导致行为“失误”（例如，情绪触发刺激暴饮暴食）（19）。我的博士学位旨在评估失去获得支持性团体成员资格对人们参与长期体重维持行为、持续健康认知和体重状况的影响。当团体治疗结束时，SSI的持续程度及其对体重维持行为的影响尚不清楚，但可能通过（重新）暴露和增加对社会和环境压力源的易感性（例如，感觉与不参与健康行为的家庭不同）有助于后来的体重恢复（20）。这个跨学科博士将研究营养（即饮食）和社会心理（即SSI）对体重循环的影响，这些影响来自于过去以群体为基础的肥胖行为干预的参与者。

Obesity (Body Mass Index (BMI)>30kgm-2) is the leading cause of premature death (1) and an urgent public health priority. Obesity is indiscriminate but particularly affects the socially disadvantaged, and is a major risk factor for conditions such as type 2 diabetes and coronary heart disease (2). Obesity is causally linked to anxiety, depression, and loneliness - in part due to repeated exposure to weight stigma (3). Ill-health effects are even more marked for people with severe obesity (BMI>40kgm-2), shortening life by 10 years (4) and being associated with increased weight stigma experiences (5). Yet, despite the exacerbated health effects and accelerating severe obesity prevalence (6), people with severe obesity remain underserved in research. Economically, obesity will cost NHS England £9.7 billion per annum by 2050 (7) and, despite its relatively small prevalence, severe obesity accounts for 24-35% of this (6); partly due to the more intensive treatments, including surgery, pharmaceuticals, and behavioural interventions (8). In short, obesity (and, increasingly, severe obesity) is common, life changing and life-limiting.Specialist NHS weight management programmes for people with obesity and severe obesity are increasingly delivered using groups (9). Group-based behavioural interventions effectively support behaviour change and weight loss in the short-to-medium term (10), reduce comorbidities risk and improve quality of life (11). However, almost 80% of programme participants regain the lost weight within 3-5 years (12). Online forums users (13) reported successful weight loss but experienced difficulty sustaining weight maintenance (both dietary and physical activity) behaviours. The resulting "weight cycling" is costly to health and the NHS due to ongoing treatment needs. Therefore, research into how the effectiveness of such specialist programmes can be extended beyond the treatment setting is needed. The current PhD aims to address this gap with an interdisciplinary approach.The Social Identity Approach to Health (14) provides the theoretical framework for this PhD and considers the health consequences of shared social identity (SSI) in members of social groups. The approach strongly implicates social identity in a range of health outcomes. In the context of group-based obesity management, it provides understanding of group treatment effects and outlines how SSI serves as a key resource supporting health-behavioural decision making and associated motivation and capability (15). Importantly, group processes have become a focus for new group interventionsSOUTH WEST DOCTORAL TRAINING PARTNERSHIPFINAL 20 Oct 2022 6supporting behavioural management of weight (16, 17) and the obesity-related cognitive and emotional stressors, including weight stigma, low self-esteem and loneliness (18), that prompt behavioural "lapses" (e.g., emotional triggers stimulating over-eating) (19).My PhD seeks to assess how the impact of losing access to a supportive group membership contributes to people's engagement with long-term weight maintenance behaviours, ongoing health cognitions and weight status. The extent that SSI is sustained when the group treatment ends and its consequence for weight maintenance behaviours is unknown, but may contribute to later weight regain by (re-) exposing and increasing susceptibility to social and environmental stressors (e.g., feeling different to family not engaging health behaviours) (20).This interdisciplinary PhD will examine nutritional (i.e., diet) and social-psychological (i.e., SSI) contributors to weight cycling in past participants of group-based behavioural interventions for obesity.