The background section situates the study within the everyday experiences of metabolic change in PD. Rather than reviewing mechanisms or constructing conceptual models, the focus remains on how metabolic health is lived within daily life. This methodology provides a foundation for understanding participant accounts presented in the results.

For individuals living with PD, metabolic change is often experienced as having more or less energy from one day to the next, thinking more clearly at some times and struggling at others.^8,9 These day-to-day shifts affect how much people feel able to do, how often they need to rest and how they move through both physical and mental tasks.¹⁰ Over time, these experiences become part of daily life and influence how easily individuals engage in activities of daily living, ultimately affecting overall QoL. In this context, QoL reflects the individual’s ability to function physically, cognitively and socially within the constraints of PD.

Quality of life is experienced in ordinary moments, such as being able to focus during a conversation, move without fear of falling or complete familiar routines.¹¹ When the body feels unstable or depleted, people may feel less independent and less willing to engage with others or with activities they once enjoyed.⁹ When the body feels steadier, those changes are often experienced as greater capability rather than simply fewer symptoms.

The ketogenic diet is experienced not as numbers or macronutrient targets but through how the body feels over time. Individuals may notice feeling fuller longer, having steadier energy, thinking more clearly or responding differently to familiar foods as the metabolic shifts take effect.^8,9 These changes are often recognised gradually as individuals pay attention to how the ketogenic diet shapes their bodily responses, daily routines and overall functioning.

Adapting to dietary change is rarely immediate or uniform. People often describe experimenting with foods, adjusting fat intake or finding personal patterns that help them feel better and stay consistent.⁹ As motor and non-motor symptoms progress, these adjustments frequently occur within the context of family life, where caregiving responsibilities increase, and daily disruptions can weigh heavily on spouses and other caregivers.¹²

Previous ketogenic dietary intervention studies in PD have reported changes in weight, metabolic biomarkers, anxiety and symptom experiences.¹³ Longer-term investigations have shown that some individuals continue to experience benefits as they learn to sustain dietary changes over time.⁹ Together, these studies provide context for understanding how metabolic interventions, like the ketogenic diet, may influence daily life in different ways.

At the same time, much of this research focuses on measurable outcomes rather than personal meaning.¹⁴ Laboratory values and symptom scores can show change without revealing what those changes actually feel like.¹⁴ As a result, important aspects of lived experience often remain unexplored.¹⁵

The purpose of this descriptive phenomenological study was to explore how a ketogenic diet affects the experiences of individuals living with PD by examining changes in metabolic health and QoL. Qualitative exploration was conducted before and after participation in a 12-week LCK intervention. The study focused on participants’ experiences of changes in mental clarity, physical function and social engagement before and after the intervention. This study sought to capture how metabolic changes were experienced and how this impacted everyday life.

Each participant (n = 16) was an adult diagnosed with PD who had enrolled in a 12-week LCK dietary intervention. Individuals ranged in age from 36 years to 81 years and represented Hoehn and Yahr stages 1 to 4 (Table 1). Participants resided in the United States and were recruited with assistance from the Colorado Parkinson Foundation. Participants in this qualitative study are a continuation of that cohort and were purposively selected based on having completed the intervention and willingness to describe their experiences.

Given that the sample was selected through participation in the parent study, no additional recruitment occurred. Rather than recruitment to saturation, thematic sufficiency was assessed through ongoing analysis, with consistent patterns observed across participants and no substantially new experiential insights emerging after approximately the twelfth interview. Subsequent interviews reinforced existing themes without contributing novel thematic content.

Eligibility criteria included a confirmed diagnosis of PD, the ability to speak and understand English, and a body mass index above the clinical cutoff of 18.5 for underweight classification. Participants were required to complete the 12-week intervention and to obtain permission from their primary care provider and neurologist before enrolment. These criteria were consistent with those used in the parent intervention study, with no additional exclusion criteria applied for the qualitative component. All participants provided informed consent before participating in interviews.

Interviews were conducted remotely via a secure Zoom platform, allowing participants to engage from their homes. This setting supported accessibility and continuity across pre- and post-intervention interviews. Conducting interviews in familiar surroundings facilitated participant comfort.

Data collection consisted of 16 semi-structured interviews lasting approximately 30 min. A single researcher conducted all interviews to maintain continuity. Interviews were prescheduled, conducted and audio-recorded via Zoom and then transcribed by Rev.com under a signed confidentiality agreement. Participants who were unable to communicate verbally completed a qualitative questionnaire and returned it to the researcher.

The interviewer has a background in health science and prior experience in metabolic and KD research. During the interview, field notes were taken to capture keywords, contextual observations and impressions deemed necessary by the interviewer. Field notes are the ‘researcher’s private, personal thoughts, ideas, and queries regarding their research observations and interviews’.¹⁷ The interviewer entered the study with an awareness of reported metabolic and symptomatic benefits associated with ketogenic dietary interventions, including expectations of potential improvements in energy, cognitive clarity and physical functioning. These notes were used reflexively to support bracketing by identifying and documenting preconceptions, allowing the researcher to remain attentive to participants’ descriptions as they were expressed. Field notes were revisited during analysis to support coding decisions, help set aside prior assumptions and ensure that emerging interpretations remained grounded in the data. Interviews were conducted with all participants before and after completion of the nutritional intervention. Interviews were guided by a semi-structured interview approach designed to elicit participants’ descriptions of their lived experiences before and after the dietary intervention. A consistent interview guide was used across pre- and post-intervention interviews, with questions adapted only to reflect timing (i.e. experiences before the diet and experiences following completion). Pre-intervention interviews focused on participants’ mental, physical and social QoL, as well as expectations for the study. Post-intervention interviews explored changes in these domains as described by participants, as well as their lived experiences with the LCK, including benefits, challenges and overall impressions. Follow-up prompts were used as needed to clarify meaning and deepen descriptions.

Upon receipt of transcripts from Rev.com, recordings were reviewed alongside transcripts to ensure accuracy and to support immersion in the data. All 16 transcripts were uploaded into ATLAS.ti, a computerised data analysis software program used to facilitate organisation and coding.¹⁸ Familiarisation with the data occurred through repeated reading prior to formal analysis.

Data were analysed using Colaizzi’s (1978) seven-step method, which includes: ‘1. Familiarisation, 2. Identifying significant statements, 3. Formulating meanings, 4. Clustering themes, 5. Developing an exhaustive description, 6. Producing the fundamental structure, and 7. Seeking verification of the fundamental structure’.¹⁹ This approach ensured that analysis remained grounded in participant descriptions while allowing patterns to emerge across accounts. In this process, meanings were derived directly from participants’ statements, with care taken to remain close to the original language and not extend interpretation beyond what was expressed during the interviews. Following this method ensured no steps are missed during the analysis while properly exploring their experiences.²⁰

Initial coding focused on identifying significant statements related to participants’ experiences before and after the dietary intervention. Codes were compared across transcripts and refined as analysis progressed, allowing themes to develop through constant engagement with the data. Analytic decisions were discussed among the research team to support the credibility and coherence of the findings.

Trustworthiness was established by addressing credibility, dependability, transferability and confirmability throughout the study.²¹ Two members of the research team independently reviewed transcripts and participated in the coding process, with codes revised as additional transcripts became available.²² Credibility was supported through member checking, allowing participants to review transcripts and request corrections or clarifications,²³ as well as peer debriefing among research team members. An audit trail and systematic documentation of analytic decisions were maintained to support dependability and confirmability.²⁴ Reflexive journaling and bracketing were used throughout the study to identify and manage potential researcher bias. Together, these strategies ensured that findings remained grounded in participants’ descriptions while supporting the rigour and transparency of the analytic process.

The study received ethical oversight approval from the Institutional Review Board at A.T. Still University (Protocol number: 2020-058) prior to data collection. Informed consent was obtained from all participants in accordance with the principles of the Declaration of Helsinki.²⁵ Before interviews began, each participant confirmed their willingness to participate and verified that they had signed the informed consent. Participant confidentiality and data security were maintained throughout the study. Audio recordings, transcripts and related documents were stored on password-protected devices accessible only to members of the research team. Identifying information was removed from transcripts, and participant data were coded to protect privacy. The study was registered with the International Standard Randomised Control Trial Number (ISRCTN) Registry through the BioMed Central (BMC) system under reference number: 38010. Registration supported transparency and public accountability of study procedures. All ethical requirements related to participant protection and data handling were observed throughout the study. A completed Consolidated Criteria for Reporting Qualitative Research (COREQ) checklist is provided as supplementary material to support transparency and methodological rigour (Online Appendix 1).

At the onset of the interview process, participants were asked to describe their expectations for participating in the study. Expectations commonly included hopes for symptom reduction, medication adjustment and weight loss. These expectations reflected participants’ understanding of their current challenges before the dietary change.

Participants frequently expressed a desire for improvements in their overall QoL and PD symptoms:

One participant described hoping for improvements in physical and psychological symptoms:

This was further reflected in the participant’s description of the relationship between anxiety and tremor, noting:

Several participants hoped that dietary changes might reduce medication burden or improve medication effectiveness. For some, participation in the study also represented an opportunity to explore emerging dietary approaches that might complement existing treatment strategies:

Weight loss was another commonly cited expectation prior to beginning the intervention:

As the pre-study interviews progressed, they yielded three major themes, including: (1) something’s not right; (2) standing on my own two feet; and (3) out of my control.

Participants frequently used the term ‘brain fog’ to describe difficulty thinking clearly or expressing themselves. Although not a clinical term, it helped participants communicate experiences that affected conversations, decision-making and confidence in social interactions. The following quotes reflect how participants described these cognitive challenges in their own words:

Other participants described becoming aware of these difficulties during everyday interactions:

About 75% of the participants discussed episodes of stress, depression or anxiety, either as a historical problem or one that occurred just before or immediately following their Parkinson’s diagnosis. These emotional experiences were often intertwined with physical symptoms, making it difficult for participants to separate psychological distress from motor changes. Participants also reflected on how these feelings influenced their outlook on the future:

Some participants realise they will have difficulty moving forward and wonder how their lives will change or how they will overcome obstacles:

Balance difficulties were a common concern among participants. Many described episodes of freezing, unsteadiness and fear of falling despite strong efforts to stay active. The following quotes illustrate how balance challenges affected everyday movement:

Participants also described recognising new physical limitations as their disease progressed:

Many participants emphasised the importance of maintaining regular exercise to prevent physical decline. Exercise routines were described as intentional efforts to preserve strength, balance and mobility. For some, the fear of losing movement served as motivation to remain physically active:

Listening to them describe their experiences, there was a sense of panic that if they stopped moving, their PD would take over:

Some participants described dystonia as a disruptive and unpredictable physical symptom. These involuntary muscle contractions affected daily functioning and, in some cases, interfered with vision and routine tasks. One participant described how dystonia affected his eyes:

Several participants described themselves as introverted, often linking this preference to physical symptoms or fear of falling. Limiting social interaction was sometimes experienced as protective rather than isolating. Participants described adjusting their social lives in ways that felt manageable:

Some described how their bodies showed signs even when they wished to remain unnoticed:

When asked about the social life, one participant responded:

Despite broader social limitations, participants often described feeling comfortable with close friends and family. Familiar relationships reduced the need to explain symptoms or manage public perceptions. These environments were experienced as safer and more accepting:

This sense of comfort was echoed by others:

Following completion of the 12-week LCK dietary intervention, participants were asked to reflect on how they felt and whether they noticed changes in their mental, physical or social QoL. Participants described both challenges and benefits associated with the intervention, including adjustments to daily routines and eating habits. From the post-study interviews, four major themes emerged.

Some participants described initial efforts to track food intake and adjust habits while also recognising the value of working towards improved health:

Others described the dietary transition as easier than expected:

They continued to say they had little difficulty buying or preparing foods associated with the ketogenic diet.

Participants described noticing changes in balance and stability after the intervention. For some, these changes occurred alongside other lifestyle efforts, such as physical therapy and weight loss, contributing to greater confidence during movement and daily activities:

Participants described moving with greater ease and less physical discomfort than before. Increased energy and reduced stiffness allowed some to resume activities they had previously limited or avoided. These changes were experienced as meaningful improvements in everyday life:

Some participants reflected on how combined efforts, such as physical therapy and dietary change, contributed to feeling better physically:

Weight loss was commonly described as noticeable and meaningful. Participants connected changes in body weight and clothing to increased physical comfort and mobility. These changes were often reinforced by feedback from others:

Participants also noticed changes reflected in the scale and waist measurements:

Others described external recognition of their physical changes:

Some participants described satisfaction with improvements seen in laboratory values and medication management. These changes were experienced as reassurance that their efforts were producing tangible health benefits. Participants also described shared engagement with spouses during this process:

Spouses often participated in reviewing health information and supporting continued effort:

Several limitations should be considered when interpreting these findings. Participants were drawn from a previously completed quantitative pilot study of an LCK intervention, yielding a small, self-selected sample of individuals motivated to engage in dietary change. As such, findings may not be transferable to all individuals living with PD, particularly those with different levels of interest or access to dietary interventions.

Experiences were captured through self-report and reflect participants’ descriptions rather than objective measures of change. The qualitative design was not intended to evaluate efficacy or establish causal relationships but to describe lived experience before and after dietary intervention. This approach prioritises depth of understanding over generalisability.

Although many participants described positive changes associated with the intervention, not all experiences reflected benefits across all domains. Some participants described challenges with dietary adherence, increased effort related to tracking requirements or more limited symptom changes. These variations were incorporated into the analysis; however, given the self-selected nature of the sample and the structured dietary intervention, individuals who discontinued or experienced greater difficulty may be underrepresented. As such, the findings may reflect a more favourable range of experiences and should be interpreted within this context.

Future research should continue to examine metabolic interventions in PD using qualitative and mixed-methods designs with larger, more diverse samples. Longitudinal studies that follow participants across different stages of disease progression and caregiving contexts may further illuminate how metabolic change is experienced over time. Integrating lived experience with metabolic and clinical outcomes will remain essential for understanding how dietary interventions are meaningfully incorporated into everyday life.