Why Keeping Weight Off Is Hard: The Role of Social Identity in Weight Loss

Obesity is a long-term and complex health condition, defined as having a body mass index (BMI) over 30. It is a major public health issue and the leading cause of early death. By 2050, obesity-related costs to the NHS are expected to reach £9.7 billion per year. While obesity can affect anyone, people from disadvantaged backgrounds are at higher risk. It also increases the chances of developing serious conditions like type 2 diabetes, heart disease, and depression, as well as feelings of loneliness. These problems are made worse by weight stigma-discrimination based on a person's weight or size. This stigma, along with health risks, is even greater for people with severe obesity (BMI over 40), yet this group is underrepresented in research.
The NHS offers specialist weight management programmes, often delivered in groups, as research shows that group support helps people lose weight in the short to medium term. However, maintaining weight loss over the long term is much harder. In fact, 80% of people regain lost weight within 3-5 years, which takes a toll on their health, confidence, and the NHS.
This PhD research is based on the Social Identity Approach to Health (SIAH), which explores how being part of social groups affects health in both positive and negative ways. In group-based weight management, belonging to a treatment group can provide motivation, support, and a sense of purpose-helping people adopt healthy behaviours. But when treatment ends, people may struggle with social and environmental challenges that lead to weight regain because they lose access to the group's shared support.
This PhD aims to improve long-term weight management beyond the end of treatment programmes. It will explore both nutritional and psychological factors-especially the role of group belonging-that influence long-term weight maintenance in past participants of group-based weight management programmes.