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

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 interventions
SOUTH WEST DOCTORAL TRAINING PARTNERSHIP
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supporting 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.