Optimising Calorie Intake for People With Amyotrophic Lateral Sclerosis: A Process Evaluation of a Complex Behaviour Change Intervention

ABSTRACT Objective To explore intervention fidelity and experiences of using a new intervention designed to optimise calorie intake in people with amyotrophic lateral sclerosis (ALS). Methods A mixed‐methods process evaluation was conducted alongside an ongoing randomised controlled trial across 15 ALS specialist centres in the United Kingdom. Data collection included 146 healthcare professional‐completed fidelity checklists, audio recordings of 5 intervention sessions, and qualitative interviews with 32 healthcare professionals, patients and informal caregivers. Results Intervention fidelity was high (88%: 1059/1204 items completed by healthcare professionals). Healthcare professionals, patients and informal caregivers within the sample recognised the intervention's value and engaged with it. Patients were motivated to use the intervention because they believed it could slow disease progression, and it gave them a sense of control. Despite challenges with the intervention, including patient concerns about weight gain and physical limitations in food preparation and consumption, patients in this sample remained committed to using the intervention. However, healthcare professionals suggested that these challenges may have negatively influenced trial recruitment and retention. Caregivers played a crucial role in supporting patients emotionally and physically, helping them to adhere to the intervention. Conclusions The intervention was feasible to implement and was delivered with fidelity. While patient engagement in this sample was strong, the intervention usability may be time‐limited as physical function declines. Therefore, the intervention may be best suited for those with slower‐progressing ALS who can manage the intervention and dietary changes. Moving forward, continued evaluation is needed to assess effectiveness and explore subgroup differences based on ALS type (slow vs. fast progressing). PPIE Contribution PPI was integral to the process evaluation. PPI members reviewed key study documents, including the Participant Information Sheet and consent forms, leading to participant materials that were clear and easily understood. They also participated in developing the intervention. Trial Registration IRAS ID 275949, ISRCTN30588041.