Theory-based process evaluation of a non-randomised single-arm pilot study investigating time-restricted eating in the treatment of type 2 diabetes-the RESET2 pilot study

BACKGROUND: This study describes a 12-week non-randomised single-arm pilot study, which was conducted to inform the design of a 1-year randomised controlled trial (RCT) on time-restricted eating (TRE) in individuals with type 2 diabetes. Core intervention components were developed to operationalize findings of a needs assessment study and the resulting initial program theory suggesting causal associations influencing TRE adherence. This study assessed the implementation and acceptance of core intervention components and activities, and participant experiences with TRE, and based on the findings, the initial program theory was refined.

METHODS: In this non-randomised single-arm study, nineteen individuals with type 2 diabetes completed 8 weeks of TRE with a 10-h eating window, followed by 4 weeks of individualised TRE (core component 1). Participants had two 1-h conversations with healthcare professionals (HCPs) at baseline and after 8 weeks to support TRE initiation (core component 2) and maintenance (core component 3). The process evaluation was conducted using a concurrent mixed methods design with emphasis on qualitative insights. Delivery and implementation of intervention activities, including visits, measurements, conversations, and phone calls, as well as the two-phase design, were evaluated. The conversations were audio-recorded to investigate the extent to which they were conducted as intended. Interviews (by a researcher) at baseline, 8, and 12 weeks explored participants' experiences, support received, and TRE implementation in daily life. The interviews were audio-recorded. A deductive qualitative content analysis approach was applied.

RESULTS: Intervention activities were delivered with high degree of consistency, and the two-phase design (strict respectively individualised TRE) was effectively implemented. Participants found the TRE intervention highly acceptable, appreciating the relevant information, well-organised trial visits, supportive HCPs, and encouraging conversations. Analysis of participants' experiences of implementation of TRE generated themes related to routines and habits, support from relatives, social life, and mental and physical challenges. Intervention components such as conversations and individual support and adjustment options were found to facilitate TRE initiation and maintenance. The initial program theory was refined in terms of how the intervention activities supported participants differently and how various contextual factors influenced their experiences and adherence to TRE.

CONCLUSIONS: Insights from participants' experiences with intervention activities and TRE performance in everyday life provided a nuanced understanding of what works, for whom, how, why, and under which circumstances in terms of TRE adherence. These findings will help tailor the following RCT intervention to the target population.

TRIAL REGISTRATION: Clinicaltrials.gov, NCT05375695. Registered 27 March, 2022: https://clinicaltrials.gov/study/NCT05375695?term=NCT05375695&rank=1.