New research has revealed important findings on the factors influencing anorexia nervosa (AN) in identical twins, offering fresh perspectives on the role of genetic and environmental factors in the development and treatment of eating disorders. The study, which focused on two pairs of identical twins who were discordant for AN – meaning one twin had the disorder while the other did not – highlighted how complex the interaction between genetic predispositions and environmental experiences can be. The findings were published in the Journal of Eating Disorders.
While previous studies have emphasised biological risk factors, this new research shifts the focus to lived experiences and personal narratives to better understand how AN develops, persists, and can be treated. The findings could play a vital role in shaping future approaches to eating disorder treatment, particularly in understanding the dynamic between siblings, especially twins, and how they can either foster or impede recovery.
Rosiel Elwyn, a PhD candidate at the University of the Sunshine Coast, reflected on the importance of such lived experiences: “This research stemmed from both my own experience and that of my co-authors, alongside my involvement in eating disorder research. While the aetiology of eating disorders has been studied for decades, recent research focuses on genetic factors that may increase vulnerability. Twin studies, which analyse shared genetic traits and their expression, are instrumental in this area.”
The study followed two sets of identical twins, both in their 20s and 30s. In one case, a twin had been living with a severe, long-standing form of anorexia nervosa, while their sibling had never developed the disorder. The second pair consisted of one twin who had recovered from a milder, atypical form of anorexia, while the other remained unaffected.
One of the most striking findings was the significant role of early life experiences. Factors such as birth weight discrepancies, premature births, and the influence of social trauma emerged as pivotal in shaping how the disorder manifested in one twin but not the other. Both pairs of twins likely shared a genetic predisposition (as indicated by their shared traits of high anxiety and obsessive-compulsivity), yet their differing environments, relationships with food, and personal encounters with trauma led to drastically different outcomes.
“The development of anorexia nervosa in each twin pair was influenced by various factors. Higher exposure to trauma, sensitivity to socio-cultural pressures like diet culture, and internalisation of gendered body ideals were linked to anorexia nervosa development. Gut and immune issues also played a role in affected twins,” Elwyn explained.
The research also shed light on how trauma, especially during puberty, could act as a trigger for anorexia nervosa. For one twin, the onset of the disorder coincided with experiences of gendered body ideals and objectification, a common theme that emerged across both cases. This suggests that sociocultural pressures and personal identity crises can compound the genetic vulnerability for anorexia nervosa, making certain individuals more susceptible to developing the disorder.
Interestingly, the study also explored the role of twin identity, noting that for some, the expectation of living identical lives created additional psychological pressures. For example, one twin’s experience of anorexia was partly influenced by the perception of being the “evil twin”, a trope exacerbated by early life jokes and family stories. This was coupled with feelings of guilt and responsibility for their sibling’s perceived wellbeing, further deepening their struggles with self-image and disordered eating.
“Unique twin-related risk factors included the internalisation of stereotypes, such as being labelled the ‘evil’ or ‘healthy’ twin, which highlights how sense of identity and sense of self are important to vulnerability for eating disorder development. In our cases, longer anorexia nervosa duration was associated with greater exposure to trauma and discrimination, body image disturbance, and atypical sensory processing,” Elwyn added.
One instance in which the healthy twin was crucial in assisting their sibling in seeking diagnosis and treatment serves as proof that the involvement of the unaffected twin was essential to the recovery process. This highlights the potential benefit of involving siblings and family members in the treatment process, an area which has not been thoroughly explored in eating disorder research. The findings suggest that having a supportive twin – who is educated about the disorder and its complexities – could significantly improve outcomes for individuals with anorexia nervosa.
Elwyn offered a similar insight: “Sibling support helped us in receiving treatment, support with eating and body disturbance, confronting stigma, managing health problems, as well as resisting diet culture and aligning with personal values.”
The research suggests that targeting relational body image, such as focusing on making self-compassionate body comparisons between twins, could be a promising avenue in therapeutic treatment. In one case, the discordance in body size between the two twins became a source of trauma but also a turning point, as the twin with anorexia began to reflect on their self-compassion and embodiment. These insights underscore the importance of developing personalised care plans that account for the unique relationship dynamics within twin pairs.
Looking forward, Elwyn is optimistic about future research in this area: “I am currently conducting a pilot study for my PhD research to investigate how traumatic experiences affect key neurobiological systems in young people with anorexia nervosa. Following this, our team will initiate a randomised controlled trial for a novel anorexia treatment aimed at targeting dysregulated brain and gut systems, potentially acting as a ‘system reset’ and enhancing responses to nutritional restoration.”
