Formative Development and Acceptability of a Lifestyle Weight Management Intervention for Breast Cancer Survivors in Greece: The NutriLife Study

<b>Background/Objectives:</b> Weight gain is frequently observed during and following breast cancer therapy. Women with overweight/obesity have poorer breast cancer prognoses and are more likely to develop comorbidities. The present study describes the development and qualitative assessment of the acceptability of the NutriLife study, a lifestyle weight management intervention with dietetic counseling and digital tools for breast cancer survivors (BCSs). <b>Methods:</b> The intervention was developed using the Medical Research Council (MRC) framework, informed by a systematic literature review and stakeholder input. Acceptability was assessed using the Theoretical Framework of Acceptability (TFA). A total of 22 BCSs with overweight/obesity participated in focus groups, and 5 dietitians/nutritionists specializing in breast cancer in Greece participated in semi-structured interviews. The data were further analyzed using thematic analysis. <b>Results:</b> Stakeholders assessed the intervention as acceptable across all TFA constructs. The intervention was characterized as supportive, easily adaptable, time-efficient, well-organized, beneficial, and professionally driven, with potential barriers including limited personal time, inadequate digital literacy, insufficient self-care, and lack of commitment. Gradually increasing goals may be helpful and less stressful, while educational resources enhance focus on these objectives, thus encouraging intervention participation. Ensuring confidentiality was perceived as central to promoting health. <b>Conclusions:</b> The evidence-based, co-participatory design of the NutriLife intervention was perceived as acceptable by the participating stakeholders and will be pilot-tested in a randomized controlled trial.