Rebecca Otte

This dissertation examines how older adults engage with, experience, and implement lifestyle interventions aimed at maintaining cognitive functioning and reducing dementia risk. It focuses on barriers and facilitators encountered in daily life, as well as on how participation in these interventions develops and is sustained over time. Using the FINGER-NL study as a central case within a structured research setting, it combines insights from controlled lifestyle intervention research with perspectives from routine dietetic practice in everyday care, to better understand how participation in lifestyle interventions is shaped, supported, and maintained over time in everyday contexts.

Lifestyle change is widely promoted as a way to support long-term health, and there is growing recognition that lifestyle behaviors are also relevant for cognitive health. However, although evidence-based lifestyle guidelines are well established and multidomain lifestyle interventions have shown promising effects on cognitive outcomes in controlled research settings, many individuals struggle to translate these recommendations into sustainable habits in daily life, suggesting that sustained behavior change may be influenced by both individual-level factors and the design and context of lifestyle interventions. This challenge is increasingly relevant in the context of population ageing and a rising chronic disease burden. Against this background, this dissertation aims to identify factors that influence engagement with lifestyle interventions, the feasibility of behavior change, and the maintenance of lifestyle changes over time.

This research is organized into two complementary tracks that together cover key phases of the lifestyle change process, ranging from engagement with structured interventions to the implementation and maintenance of lifestyle changes in everyday life.

The first track (Chapters 2–5) focused on older adults’ experiences within the FINGER-NL multidomain lifestyle intervention, addressing motivation, engagement, and the feasibility of implementing lifestyle changes in daily life. The second track (Chapters 6–8) shifted the focus to routine care, exploring how lifestyle changes were supported, adapted, and maintained over time from the perspectives of dietitians and their patients.

Chapter 2 explored why older adults chose to participate in the FINGER-NL lifestyle intervention and what they expected would help or hinder their initial engagement. The findings showed that participation was mainly motivated by personal relevance and perceived personal gain, particularly the desire to maintain or improve cognitive health, often shaped by concerns about developing dementia and experiences in participants’ social environment. Public interest played a more limited role. Knowledge about dementia risk reduction was generally limited and largely informed by personal experiences. Participants also identified anticipated barriers and support needs, suggesting that motivation alone was insufficient to ensure engagement.

Chapter 3 examined lived experiences one year into the intervention. The findings showed that engagement and adherence varied over time and between participants in both the high-intensity (HI) and low-intensity (LI) groups. Among HI-group participants, motivation was not static: some experienced declining motivation when encountering barriers, while others became more motivated as they noticed positive effects or integrated new habits into daily routines. Diet and physical activity remained the most salient lifestyle domains and were also the areas in which participants reported the most changes. Participants frequently described making selective choices about which intervention components to follow, often supported by lifestyle coaches, and experienced this flexibility as helpful for sustaining engagement. In the LI-group, participants often expressed disappointment about limited guidance, yet some initiated lifestyle changes independently, influenced by study participation and concerns about cognitive decline. Across both groups, participants were generally aware of their group allocation, illustrating the practical challenges of blinding in lifestyle interventions.

Building on these findings, Chapter 4 examined how engagement and lifestyle change developed over time by identifying distinct participation trajectories using ideal-type analysis of the longitudinal interview data collected at baseline, 12 months, and 24 months. Six trajectories were identified across the high-intensity (HI) and low-intensity (LI) groups. These trajectories illustrated different patterns of change, ranging from early enthusiasm followed by decline, to gradual adoption and consistent adherence in the HIgroup, to self-directed change and passive participation in the LI-group. Across both groups, some participants were characterized by trajectories interrupted by major life events. Rather than representing fixed categories or stable groups, the trajectories were used as an analytical tool to illustrate the dynamic and fluctuating nature of engagement over time. Participants differed not only in which lifestyle behaviors they changed, but also in how they responded to the support provided. In the HI-group, structured guidance and regular contact helped sustain motivation across domains, while in the LI-group, information alone was often insufficient to prompt or maintain change. Across both groups, major life events frequently disrupted engagement, regardless of initial motivation. These findings showed that sustained lifestyle change followed multiple trajectories and required support that could adapt to changing circumstances over time.

Chapter 5 built directly on insights emerging from Chapters 2–4, showing that participants’ decision to take part in the FINGER-NL trial was mainly driven by concerns about cognitive decline and dementia rather than by general health goals. These insights raised the question of how such dementia-related beliefs and motivations related to the presence of modifiable, lifestyle-related dementia risk factors at baseline. Chapter 5 therefore focused on motivation and beliefs regarding dementia risk reduction, assessed with the Motivation to Change Lifestyle and Health Behaviors for Dementia Risk Reduction (MCLHB-DRR), a questionnaire that captured how people thought and felt about dementia risk, including perceived risk, concerns, and motivation to address lifestyle-related risk factors. Only a limited number of psychological factors were associated with specific lifestyle-related dementia risk domains, and these associations differed across domains. Motivation- and belief-related subscales showed weak and inconsistent associations with dementia risk profiles. Overall, the presence of dementia-related lifestyle risk factors appeared to be more related to sociodemographic characteristics than to individual motivation and beliefs. These findings aligned with the qualitative results from Chapters 2–4, which showed that such risk factors were closely linked to everyday routines, habits, and social circumstances.

Track 2 began in Chapter 6 by examining general lifestyle interventions for obesity to draw methodological insights relevant to understanding complex behavior change. By doing so, we aimed to draw on existing knowledge in this field to better understand how different intervention components interacted in more general lifestyle change contexts. Chapter 6 addressed the question of which components were truly relevant, or even indispensable, when designing a lifestyle intervention. Using Qualitative Comparative Analysis, this chapter showed that successful population-level weight loss emerged from specific combinations of intervention components rather than from any single element. The co-occurrence of dietary change, physical activity, and behavioral change strategies was most consistently associated with success, whereas none of these components alone was sufficient or necessary. These findings highlighted the multifaceted and context-dependent nature of lifestyle interventions and showed that effectiveness was shaped by how components worked together rather than by isolated elements such as intervention duration or group setting. As such, this chapter illustrated the methodological value of configurational approaches for studying complex lifestyle interventions, rather than providing direct evidence for cognitive-health intervention design and was therefore guiding for the analysis in Track 1.

In Chapters 7 and 8, we continued Track 2 by focusing on dietetic treatment of adults with obesity in primary health care. Chapter 7 examined which components dietitians considered key to successful treatment, shifting attention from intervention design to everyday clinical practice. Based on interviews and focus group discussions with Dutch dietitians, the findings showed that building a trusted relationship and connecting treatment to individual patient needs were seen as central to success. Several interrelated components related to relationship-building, behavior change support, and tailored advice were identified. The findings highlighted the importance of the dietitian’s counselling role, particularly in addressing motivation, self-efficacy, health literacy, and experienced barriers, and showed how patient characteristics influenced the choice and use of treatment strategies.

Chapter 8 shifted the focus from the dietitians to the lived experiences of patients with obesity receiving dietetic treatment in primary health care. Patients perceived personalized treatment as the foundation of successful care, with feeling heard, understood, and supported described as central to their engagement. A strong patient–dietitian relationship, shaped by the dietitian’s attitude, professionalism, and way of working, was described as crucial for building trust and motivation. Patients emphasized the importance of a holistic approach that extended beyond dietary advice alone, including attention to psychological factors, life context, and long-term behavior change. Clear, practical, and tailored advice was also seen as essential for translating recommendations into daily life. Taken together, Chapters 7 and 8 showed substantial overlap between dietitians’ and patients’ perspectives, suggesting that effective dietetic treatment for obesity depended on approaches that were responsive to individual needs and circumstances rather than standardized protocols alone.

In Chapter 9, the findings of this dissertation were brought together in a general discussion reflecting on what lifestyle interventions aimed at supporting cognitive health could, and could not, achieve by integrating insights from both research and routine care. The discussion integrated insights from studies conducted in controlled research settings with findings from Track 2, which examined lifestyle change beyond the research context from the perspectives of dietitians and patients in routine care. Across the dissertation, a consistent picture emerged: while lifestyle change in support of cognitive health was possible, it was also complex and demanding. Participants were often strongly motivated by concerns about cognitive decline, but acting on this motivation depended on practical, emotional, social, and contextual factors.

Across chapters, motivation alone appeared insufficient to sustain behavior change, and no single intervention component proved decisive. Instead, behavior change emerged from the interaction of daily routines, available resources, personal circumstances, and the organization of support. A clear contrast emerged between research-based lifestyle interventions, which emphasized structure and standardization, and routine care, which relied more on flexibility, personalization, and long-term relationships. Across both contexts, relational aspects, such as feeling heard and receiving advice that fit one’s own life, played a key role in sustained engagement.

Chapter 9 concluded by considering the practical implications of these findings. While an intensive research-driven intervention such as FINGER-NL was not easily transferable to routine practice in its current form, the lifestyle behaviors it targeted were relevant beyond dementia prevention alone. In the general discussion, these findings were briefly placed in a broader context, with some reflection on how attention to cognitive health might be embedded within existing care structures, for example through digital support and interprofessional collaboration, and how this could relate to everyday life.