Abstract
BACKGROUND: Emerging research suggests indications for both Mediterranean and ketogenic diets in Parkinson's disease (PD), with hybrid Mediterranean-ketogenic interventions potentially conferring maximal benefit. However, the acceptability of these interventions in individuals with PD (PwPs) remains to be established. OBJECTIVES: To explore and compare factors affecting PwPs' experiences with and adherence to an 8-wk Mediterranean-ketogenic (MeDi-KD) versus an 8-wk medium-chain triglyceride (MCT)-supplemented Mediterranean (MeDi-MCT) diet. METHODS: Forty-eight PwPs took part in ≥1 phase of the crossover trial. Sixty-seven semistructured interviews were completed by 44 participants after each intervention. Interview questions, structured using the Theory of Planned Behavior (TPB), explored how participant attitudes, control beliefs, environmental contexts, and social influences impacted study diet adherence. Reflexive thematic analysis was applied to interview transcripts. RESULTS: Two subthemes each emerged under of the overall themes of "Attitudes," "Perceived behavioral control," and "Subjective norms" within the TPB framework. Attitudes toward MeDi-KD and MeDi-MCT compositions were polarized, based on varying levels of familiarity with similar dietary patterns, diverging taste preferences, and wide-ranging expectations of effects on PD-specific and general health outcomes. Capability and resources grouped together naturally under the "Perceived behavioral control" theme. Within this domain, competing personal responsibilities, attentional resources diverted to disease management tasks, PD-related apathy, and motor deficits compromising cooking skills, all proved especially problematic during the labor-intensive MeDi-KD phase. In the "Subjective norms" domain, household and cultural acceptance of study diets proved crucial for sustained adherence. Our study's registered dietitian played a pivotal role in supporting adherence through the direct provision of informational, instrumental, and social support, as well as by engaging care partners to bolster social support within the home. CONCLUSIONS: Our qualitative analysis illuminates behavioral and contextual determinants of adherence to keto-adapted MeDis in PwPs, informing more sustainable dietary implementation strategies relevant both to future trial design and dietetics clinical practice.This trial was registered at clinicaltrials.gov as NCT05469997.