Introduction

Eating disorders are serious mental illnesses with severe consequences on the somatic, psychological, and social levels [1,2]. The diagnoses described in the current version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5 [3]) include three main disorders: 1) anorexia nervosa, which is characterised by severe dietary restriction and a weight below a healthy body mass index (BMI); 2) bulimia nervosa, which is characterised by episodes of compulsive eating and compensatory behaviours for weight control; and 3) binge eating disorder, which also includes compulsive eating episodes but without compensatory behaviours. Sub-threshold forms of these disorders, manifesting with only some symptoms of the full syndromes, also cause significant suffering [4]. An epidemiological study has shown that, in Switzerland, the lifetime prevalence rates of these disorders, calculated by adding lifetime prevalence estimates for anorexia nervosa, bulimia nervosa, binge eating disorder, any eating disorder, sub-threshold binge eating disorder and any binge eating, were 17.5% for women and 7.8% for men [5]. According to the authors of this study, these prevalences were comparable to those of other westernised countries and even higher for bulimia nervosa, which is a pathology strongly influenced by culture [6].

Mental disorders frequently develop in adolescents or young adults, and interfere with the developmental tasks required during these periods [7]. These disorders are likely to become established in adulthood, which is why public health initiatives aimed at youth can greatly contribute to the health of the community [7]. Regarding the field of eating disorders more specifically, people with eating disorders often feel ashamed of their disorder, which prevents them from seeking help [8]. This delays the possibility of treatment whereas early intervention improves treatment outcomes [9]. The distress and functional impairment caused by eating disorders, together with eating disorders correlation with depression, anxiety, substance use disorders and elevated risks of suicide attempts, reinforce the need of intervening with prevention interventions before eating disorder onset [1,10,11]. Moreover, there is a lack of treatment facilities providing specialised and evidence-based treatments for eating disorders [12], and evidence-based treatments do not suit every patient, with remission rates not superior to 50–60% of the patients with bulimia nervosa or binge eating disorder [13]. Finally, the costs generated by these disorders are underestimated; because they are not systematically declared, it is indeed difficult to have an objective view of the missed working days or of the complications that they cause. The critical period during which eating disorders develop, the difficulty of treating these disorders, the suffering they cause, together with the costs they generate, highlight their public-health significance, and lead researchers to recommand the development and evaluation of prevention interventions for eating disorders targeting young adults [14].

The prevention interventions built on the Dual Pathway Model [15] as theoretical foundations are among the most effective [16,17]. Stice proposed this model after a meta-analysis of the risk factors leading to compulsive disorder type [18]. It includes two identified pathways leading to the development of compulsive eating disorders: 1) dieting and 2) negative affect (Fig 1), with body dissatisfaction as the necessary and common risk factor.

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Fig 1. Stice’s Dual Pathway Model.

https://doi.org/10.1371/journal.pone.0259796.g001

Based on this model, Stice and colleagues conceptualised a prevention intervention that targets the internalisation of the societal beauty ideal of thinness (thin-ideal internalisation in the model in Fig 1) in order to intervene upstream of body dissatisfaction. This intervention, called “Body Project” (BP), was first evaluated in comparison with a control group without intervention, in female undergraduates aged 18–22, with body dissatisfaction (N = 30), in the United-States (US) [19]. Then, the BP was compared to a placebo intervention specially designed for the study: the “Healthy Weight Program” (HW) in US young women aged 17–29 with body dissatisfaction [20]. When the two interventions were compared, the BP participants showed significant decreases in thin-ideal internalization, body dissatisfaction, dieting, negative affect, and bulimic symptoms. In parallel, decreases in thin-ideal internalization was not observed the HW participants, however this placebo intervention produced significant improvements, albeit smaller, of the other outcomes variables. To clarify these unexpected findings, a four-armed study compared the two intervention programmes with an emotional writing condition and a control group without intervention and followed up for up to three years in 481 US adolescent girls [21,22]. The results were favourable to the BP and the HW compared to the two control conditions, with a reduction in the onset of eating disorders at three years of 60% for the BP and 61% for the HW.

Since then, these two prevention interventions have been evaluated in various contexts. The BP intervention provided greater decreases of eating disorders risk factors than a video-control condition, whether led by a clinician, peers or delivered by an Internet platform [23]. The peer-led version of the BP turned out to produce the greatest reduction of eating disorders onset after four years, compared to the other form of program delivery [24]. The BP intervention was evaluated in other cultural context than US, for example Brazil [25] and Sweden [26], with similar outcomes, and without the need for cultural adaptation [25]. The BP and the HW interventions were also adapted and proposed to women athletes [27]. Both interventions significantly decreased eating disorders risk factors in this population, and the qualitative results suggested the athletes seemed to prefer the HW intervention. The BP is the eating disorder prevention programme which has collected the largest number of multiple independent replications of trials assessing its efficacy and effectiveness in reducing eating disorder risk factors and symptoms [28]. Because of the strong empirical support garnered by the BP in the US, scholars have recommended the examination of its potential to reduce eating disorders onset in Europe as well, which is in need of efficacious eating disorder prevention intervention [29]. Replication trials to assess the effectiveness of the HW, which is the only programme who has successfully addressed the prevention of eating disorders and obesity, are also needed [29].

Most studies evaluated the BP and the HW interventions in a context of selective prevention, intended for people with risk factors. Therefore studies included young women with body dissatisfaction. The BP and the HW interventions are both aimed at older adolescents and young adults, typically students. Excessive concerns with body image and disturbed eating behaviours often appear in adolescence and usually have not been addressed due to many reasons, from a desire to manage the problem by oneself, to a lack of time, or a lack of availability of treatment facilities [30–32]. But when young people arrive at university or enter higher education, the stress due to academic competition, the new environment, and the empowerment that accompanies this new stage of life may increase already existing difficulties [33]. Therefore, young women who are at-risk because of body dissatisfaction could greatly benefit from targeted interventions.

To our knowledge, no study has been carried out in Switzerland to evaluate an intervention for the prevention of eating disorders. Public health in French-speaking Switzerland lacks programs based on evidence in this field. This protocol presents a preliminary study to evaluate the acceptability and the effectiveness of the BP and HW interventions for female students in French-speaking Switzerland. Both of them have produced significant effects. The BP have produced larger effects [21,22], however the HW might be better accepted by certain sub-groups, such as athletes [27]. This is why we are interested in both of them. The study is preliminary in the sense that we want to collect participants’ satisfaction with each of the two interventions in order to assess their acceptability. A French version of the BP already exists, but no studies has yet been published on its effectiveness. The HW program will be translated in French by us. The script will be first translated literally and then adapted according to the Swiss recommendations for a healthy nutrition and physical activity. However, the core of the intervention, which is to set small objectives to modify permanently one’s dietary intakes and physical activity in order to reach energy balance, and discuss their attainment in group, will be kept identical. Besides, the two interventions will be compared to a waiting list to assess the interventions effectiveness, with a power able to detect large effect size.

The goal of this study is to assess the following three hypotheses:

1. The acceptability of the two interventions, assessed by the number of sessions that the participants attend, their satisfaction with the intervention, and qualitative comments provided by the participants, will be good for both interventions;
2. The two interventions BP and HW will improve body dissatisfaction (primary outcome) as well as thin-ideal internalisation, dietary restraint, negative affect, and eating disorder psychopathology (secondary outcomes), compared to a waiting list;
3. The improvements observed in the intervention groups (BP and HW) will be maintained after one month of follow-up.

Materials and methods

Study design

To compare the BP and HW interventions to a waiting list, we plan to carry out a three-arm randomised controlled study, including female students from French-speaking Switzerland. We will recruit 90 participants over a 12-month period, starting in January 2021. Participants will be randomly assigned to one of the three arms of the study. Both interventions are composed of four weekly sessions and last one month. The waiting list duration will be set to one month in a parallel way. Participants will be evaluated before (T0) and after (T1) the interventions or the waiting list. The interventions are given to groups of six participants and will start each time a group is formed following randomisation. Following the interventions, the participants will have one month of follow-up without contact with the investigators before a final evaluation (T2). To maximise the feasibility of the study regarding funding and university calendar, participants in the waiting list group will receive the BP intervention following the one-month waiting period instead of waiting until the end of the follow-up assessments. They will be evaluated at the end of the intervention (T2). The procedure is described in Fig 2.

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Fig 2. Flowchart illustrating recruitment and assessment of the participants through the study.

Adapted from the CONSORT 2010 flow diagram.

https://doi.org/10.1371/journal.pone.0259796.g002

Discussion

This study will provide initial results on the acceptability and effectiveness of the BP and HW interventions in French-speaking Switzerland. These results will be disseminated through scientific articles and at conferences on eating disorders and body image. In order to disseminate the results in the community, we will communicate them to the two main French-speaking websites dedicated to adolescents and young adults health promotion. Potential cultural adaptations that might emerge from the participants’ comments will be considered and discussed with the designers of the interventions, before being adopted. We do not expect major adaptations, since at least the BP programme was used successfully in other cultures than the US without fundamental change [25,26]. In addition, these preliminary data will be used as a basis to write a grant proposal for national funding agencies for investigating the mediating or moderating factors involved in the prevention of eating disorders. In particular, the mechanisms at play in the HW are not yet well understood [53]. An analysis of the stability of the effects of interventions, as well as their effect on the development of eating disorders, requires a larger sample and a longer follow-up period.

This preliminary study will include limitations. A truly "preventive" effect in relation to the onset of an eating disorder will not be appreciable, as longer-term measures are needed. Therefore, we use a "proxy", that is, the measure of a risk factor, which is body dissatisfaction in this case. The disclosure that both programmes should aim at reducing body dissatisfaction could impact the outcomes, however this disclosure is deemed necessary to recruit participants with a sufficient level of body dissatisfaction. Then, this preliminary study will include a sample size that allows the detection of only large effects. We will not assess the stability of the interventions after one month. This study will include only female participants, as the majority of the studies on the BP and HW interventions [17]. Few studies have been conducted on mixed groups, and the results obtained have been less convincing, with young women benefiting less from the effects of interventions when young men were included (e.g. [54]). However, this is as concern because young men also experience body dissatisfaction with impact on their health [55]. Among the strengths of this study, the sample size needed to show a pre-post effect was calculated, which should ensure that we are able to detect a large effect size. Both interventions have shown positive effects in other countries (e.g. [25,26]). Both interventions have specific features, which is why we are evaluating them both. The study design makes it possible to assess their effect in comparison to no intervention in a community setting.

Conclusion

This study is a first step into the field of selected prevention of eating disorders in Switzerland, where eating disorders are highly present and evidence-based prevention interventions are still lacking.