Ketogenic Diet-Specified Interventions in Neurodegenerative Disease Mechanisms

Ketogenic Diet and Neurodegenerative Diseases

Executive Summary

The ketogenic diet (KD) and ketogenic interventions (e.g., diets supplemented with MCTs, modified KD protocols, and strategies aimed at increasing β-hydroxybutyrate [HB]) are described in the literature as potentially beneficial for several neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). However, clinical data remain limited [1–3].

The most consistent clinical signal in AD concerns improvement in daily functioning and quality of life after 12 weeks of modified KD in a crossover randomized study (ADCS-ADL, QOL-AD), despite a lack of statistically significant improvement in ACE-III scores [4].

In PD, clinical data suggest that ketogenic interventions may lead to greater benefits in non-motor domains and quality of life compared to improvements in motor outcomes. In an RCT with 47 patients comparing KD to a low-fat diet, both groups improved MDS-UPDRS scores, but KD was associated with greater improvement in non-motor symptoms. A review of six studies involving 152 patients indicated small to moderate effects on quality of life, particularly in non-motor areas such as fatigue and sleep, with inconsistent results and marginal/inconsistent motor benefits [1, 5].

Mechanistically, KD and ketone bodies (KBs) are associated with switching metabolism towards fatty acid oxidation and ketone production, improved mitochondrial function, reduced oxidative stress (e.g., by lowering ROS generated by complex I), activation of antioxidant pathways (Nrf2), inhibition of neuroinflammatory pathways (NF-κB, NLRP3, IL-1β), signaling, epigenetic phenomena (e.g., HDAC inhibition), and gut–brain axis modulation through effects on the microbiome [1, 6].

The largest limitation of current evidence is the small sample sizes, short intervention durations, frequent lack of randomization and control groups, as well as protocol heterogeneity and inconsistent ketosis criteria. There is a strong need for large, long-term, prospective, blinded randomized controlled trials (RCTs) [3, 7, 8].

Introduction

The ketogenic diet is described as a “biochemical model of starvation,” promoting the use of ketone bodies as the dominant fuel source instead of glucose for the central nervous system [6].

Clinical practice and research on neurodegenerative conditions utilize several approaches that aim to achieve ketosis, defined as blood ketone levels around [9]. Variants implemented in studied protocols include modified KD, such as a 12-week crossover randomized KD study in AD, and MCT-based ketogenic strategies, as highlighted in two AD studies that demonstrated cognitive improvements and incorporated MCT [9, 10].

Additionally, a modified Atkins diet (MAD) as a ketogenic intervention was tested in a 12-week RCT on individuals with mild cognitive impairment (MCI) due to early AD [11]. Extraneous ketones, including exogenous β-OHB (exogenous HB), are also mentioned in preclinical studies as potential interventions alongside KD and MCT. However, these data do not establish clinical efficacy in humans [6].

Neuroprotective Mechanisms

Bioenergetics

KD induces a metabolic switch towards ketone production and fatty acid oxidation, which is associated with improved mitochondrial function, anti-inflammatory capabilities, endogenous antioxidants, anti-apoptotic activity, and enhanced energy supply for the brain [1].

HB and acetoacetate reduce ROS production by complex I of the respiratory chain and enhance hippocampal survival by reducing ROS, providing one of the mechanistic foundations for neuroprotection [1].

Oxidative Stress and Neuroinflammation

KD has been linked to activation of the Nrf2 pathway and attenuation of oxidative stress [1]. HB elevation induced by KD may inhibit inflammation by blocking IL-1β expression and influencing the inflammasome NLRP3, which controls the activation and release of caspase-1. KD and HB directly modulate neuroinflammation via effects on microglial polarization towards M2-like phenotypes, which support regeneration and neuroprotection [1].

Additionally, KD inhibits activation of NF-κB inflammatory factors, further reducing neuroinflammation [6]. Ketones also inhibit the NLRP3 inflammasome, controlling the activation of caspase-1 and release of pro-inflammatory cytokines such as IL-1β and IL-18 [6].

Signaling and Epigenetics

KD has been shown to inhibit histone deacetylases (HDACs), which are involved in chromatin structure and gene accessibility modifications [6]. Research also suggests KD may activate PPAR-α mediated by fatty acids, leading to inhibition of glycolysis and modulation of fatty acid metabolism [6].

Gut-Brain Axis

KDs have been demonstrated in synthesis studies to affect the abundance and diversity of the gut microbiome, as well as microbial-derived molecules involved in central nervous system homeostasis and neuroprotection [1].

Neurological Disorders and Ketogenic Diet

Alzheimer’s Disease and Mild Cognitive Impairment

In AD/MCI, ketogenic interventions are rationalized based on impaired glucose metabolism, accumulation of β-amyloid (Aβ), and tau pathology. As ketone metabolism in the brain remains functional in AD, it may compensate for brain insulin resistance and glucose metabolic deficits [4, 13].

Clinical Evidence

Clinical evidence includes a crossover RCT in confirmed AD, where KD improved daily functioning (ADCS-ADL ; ) and quality of life (QOL-AD ; ). ACE-III scores increased non-significantly [4].

Another three-month one-arm trial in patients with mild AD showed that the intervention was well-tolerated without serious adverse events. Cognitive improvements in the ADAS-Cog scores were observed after three months for patients achieving a consistent or intermittent state of ketosis [14].

A study testing MAD in MCI due to early AD showed improvements in Memory Composite Scores and medium effect sizes, though adherence to the diet was challenging [11]. Reviews highlight cognitive improvements in small trials but note inconsistent results and the absence of improvement in cognition for some participants with mild–moderate AD [1, 9, 10].

Mechanisms Specific to AD

KD promotes usage of KBs as the main fuel source for the CNS, forming the basis of the “alternative fuel” hypothesis in AD. KBs reduce glycolytic ATP production and enhance mitochondrial oxidation, which is associated with metabolic benefits such as ketosis, increased serum lipids, lower glycemia, and protection against neuron loss via apoptosis and necrosis [6].

KD may suppress NF-κB activation and inflammasome NLRP3 to reduce inflammatory responses, limiting the release of pro-inflammatory cytokines like IL-1β and IL-18 [6]. Additionally, KD's inhibition of HDAC may incite long-term changes in gene expression and neuroplasticity [6].

Data from animal models indicate KD, exogenous β-OHB, and MCT reduce brain Aβ levels, mitigate Aβ toxicity, and improve mitochondrial function. In transgenic models, soluble Aβ deposits decreased by 25% following 40 days of KD treatment [6].

Practice and Safety in AD and MCI

Achieving ketosis and adherence to KD are critical limitations in implementing these interventions. In a single-arm study, five participants failed to maintain ketosis and dropped out, typically having more advanced dementia [14].

In an RCT involving MAD for MCI, only two participants in the MAD arm adhered to the intervention protocol, suggesting intense support and monitoring are required to achieve metabolic objectives [11].

In a three-month study, the intervention was well-tolerated with no major adverse events [14]. Analysis of dietary quality during KD revealed deficiencies in certain micronutrients (e.g., calcium, magnesium, potassium, vitamins D and E) and lower fiber intake, highlighting the need for careful dietary planning and supplementation [15].

Evidence Limitations

Systematic reviews emphasize that clinical evidence for KD in neurodegenerative diseases remains limited and heterogeneous, often relying on pre-post designs without randomization or control groups. Large RCTs with extended patient follow-ups are needed to explore KD’s therapeutic potential definitively [7, 8].

Parkinson’s Disease

In PD, ketogenic interventions are described as a potential adjunct strategy addressing multiple aspects of pathology, though reviews caution the limited availability of clinical evidence and the need for careful interpretation [16].

Clinical Evidence

An RCT involving 47 patients compared a low-fat diet with KD, with both groups showing significant reductions in MDS-UPDRS scores. Notably, the KD group exhibited greater improvement in non-motor symptoms [1].

In an uncontrolled 28-day study, PD patients experienced a 43% average reduction in UPDRS scores after KD exposure, a promising signal for symptomatic efficacy despite the lack of a control group [17].

Short-term KD supplemented with MCT underwent feasibility testing in a randomized trial. Despite good adherence among most participants (>90%), the study was terminated early due to a lack of significant mobility improvement in TUG/UPDRS-3 outcomes [18].

A review encompassing six studies with 152 patients indicated that KD provided small-to-moderate effects on quality of life, particularly in non-motor domains like fatigue and sleep, while marginal or inconsistent motor benefits were reported [5].

In a 12-week single-arm study, KD significantly improved MDS-UPDRS III motor scores and various non-motor symptoms, including constipation, daytime sleepiness, anxiety, and depression [19]. It also improved cognitive functions, aligning with the hypothesis that non-motor domains may be particularly sensitive to metabolic interventions [19].

Case studies include reports of individuals with early-stage PD experiencing improved biomarker profiles and symptom relief after adhering to KD [20].

Mechanisms Specific to PD

HB is suggested to protect dopaminergic neurons and mitigate PD symptoms in mouse models. Mechanistically, KD may reduce oxidative stress and inflammation through HB-mediated inhibition of NF-κB and inflammasome NLRP3 activity [5, 12]. HB’s interaction with the HCAR2 receptor on microglia and macrophages is proposed to suppress neuroinflammation [12, 21].

In MPTP-induced mouse models, KD decreased levels of pro-inflammatory cytokines such as IL-1β and TNF-α, reduced microglial activation, and improved dopaminergic neurotransmission and motor functions [12].

Gut-Brain Axis

A 12-week KD study noted changes in gut microbiota composition, including increased Enterococcus and Synergistota and decreased Alloprevotella. These microbiota shifts were associated with clinical improvements, potentially through gut-brain regulatory mechanisms and anti-inflammatory pathways [19].

Practice and Limitations in PD

Reviews highlight small study sizes, short intervention duration, and variable endpoints as common limitations, indicating the need for robust trial designs to better understand the long-term efficacy of KD in PD [5, 16].

Amyotrophic Lateral Sclerosis

In ALS, ketogenic diet literature is limited, with few clinical data available for neurodegenerative diseases as a group. Large, randomized, double-blind controlled trials are recommended to determine KD's effects on progression and symptoms in ALS and related diseases [1, 3].

Multiple Sclerosis

Clinical evidence concerning KD in MS is scarce. Current reports describe its application in neurodegeneration as primarily theoretical, given the lack of human studies [22]. Despite the prevalence of immunological therapies in MS, there is no definitive treatment for progressive forms, which underscores the need for alternative strategies addressing neurodegeneration [22].

Mechanisms Specific to MS

Mitochondrial dysfunction may lead to reduced ATP availability, connected to the axonal damage that characterizes neurodegeneration. KD has been shown in vitro and in animal models to increase ATP production, support mitochondrial biogenesis, avoid dysfunctional bioenergetic pathways, elevate antioxidant levels, and reduce oxidative damage [22].

The anti-inflammatory effects of KD may involve HB-mediated suppression of the inflammasome NLRP3, independent of starvation-induced mechanisms such as AMPK activation or glycolysis inhibition [22]. Since ATP elevation and mitochondrial improvement correlate with axonal survival, KD may offer therapeutic potential for the neurodegenerative components of MS, pending clinical evidence [22].

Safety

Short-term ketogenic interventions have been generally well-tolerated. For example, in a three-month AD study, no severe adverse events were reported [14]. Furthermore, an RCT crossover in AD revealed high adherence to KD, with only one dropout attributed to the diet [4]. In PD, short-term KD supplemented with MCT showed a high participant adherence (>90%) with good acceptability [18].

Nutritional analyses revealed potential risks of micronutrient deficiencies and reduced fiber intake during KD, emphasizing the need for dietary planning and supplementation [15].

Evidence Limitations

Systematic reviews highlight the limited and heterogeneous clinical evidence available for neurodegenerative diseases. The potential therapeutic value appears to be most relevant for early-stage conditions or patients with favorable metabolic and genetic profiles [2]. Large-scale, long-term RCTs are essential to clarify KD's role in treating diseases like MS and ALS [7, 8].

Clinical Evidence and Limitations

At the same time, it is noted that clinical evidence is scarce, and most existing studies are small in number, often uncontrolled, and limited to short-term effects of the ketogenic diet (KD) [3].

Alzheimer's Disease (AD) and Mild Cognitive Impairment (MCI)

In the area of AD/MCI, it is emphasized that the few human studies often feature pre-post designs without control groups or randomization, which limits causal inference [7].

Parkinson's Disease (PD)

For PD, limitations include small populations and short intervention times, which hinder the assessment of long-term effects and contribute to inconsistencies in study outcomes, particularly concerning motor results [5, 16].

Multiple Sclerosis (MS)

For MS, the evidence is explicitly described as theoretical since data from human studies are lacking, making it impossible to formulate clinical recommendations regarding efficacy [22].

Research Directions

Syntheses on neurodegenerative diseases unequivocally recommend large, long-term, prospective, randomized, double-blind controlled trials to determine whether KD can alleviate or treat the development, progression, and symptoms of neurodegenerative diseases [3].

AD/MCI

In the area of AD/MCI, there is an emphasis on the need for large randomized controlled trials (RCTs) with long-term observation due to the limitations of existing designs and inconsistencies in cognitive outcomes [8, 9].

PD

Research directions for PD include determining whether ketogenic interventions primarily affect non-motor domains (such as fatigue, sleep, autonomic symptoms, and cognition) and their impact on quality of life compared to other dietary patterns. This aligns with review findings demonstrating small-to-moderate improvements in quality of life (QoL) and marginal motor effects [5].

Mechanistic Studies

In mechanistic studies, a rational direction is the integration of axes such as mitochondrial bioenergetics (ATP/ROS), neuroinflammation (NF-κB, NLRP3, IL-1β), signaling (HCAR2), and potential microbiotic mediators, as these elements are repeatedly identified as targets of KD/ketones [1, 21].

Practical Implications for Clinicians

Ketogenic interventions should only be considered as potential adjunctive treatments because reviews highlight the limited and heterogeneous clinical evidence base and the need for large RCTs before making conclusions about their impact on the progression of neurodegenerative diseases [2, 3].

AD

In AD, the most clinically justified hypothesis, based on available data, is the possibility of short-term improvements in daily functioning and quality of life with sustained ketosis. However, improvements in global cognitive tests may be modest or inconsistent [4, 9].

MCI and AD

For MCI and AD, practical implementation should consider that adherence to the diet and achieving ketosis are frequent barriers (e.g., many participants fail to achieve ketosis or discontinue in single-arm studies, and only two met adherence criteria in a modified Atkins diet arm). This implies the need for monitoring (e.g., blood ketone measurements) and dietary support [9, 11, 14].

PD

In PD, it is essential to realistically communicate to patients that, although some studies suggest improvements in non-motor domains and quality of life, motor outcomes in reviews are often marginal or inconsistent. In one randomized feasibility study, no significant effect on TUG/UPDRS-3 was observed, and the study was discontinued due to "futility" [5, 18].

Nutritional Quality in KD

For all discussed conditions, planning a KD intervention should include assessing nutritional quality and the risk of deficiencies (e.g., calcium, magnesium, potassium, vitamins D and E, and fiber), as imbalances in micronutrient intake have been demonstrated in analyses of KD [15].

MS

In MS, due to the lack of clinical data in humans, KD cannot be recommended as an intervention with proven efficacy. Any decisions should consider that the evidence remains theoretical [22].

Summary of Clinical Signals and Limitations

Summary

Collected data indicate that ketogenic interventions in neurodegeneration have a strong mechanistic justification encompassing mitochondrial bioenergetics, oxidative stress, neuroinflammation (NF-κB, NLRP3, IL-1β), HCAR2 signaling, epigenetics (HDAC), and potential gut mediators [1, 6, 21].

Clinically, the strongest and most measurable signals in the provided material concern short-term improvements in functioning and quality of life in AD (in RCT crossover studies) and improvements in non-motor domains/quality of life in some PD studies. However, inconsistencies in motor outcomes and methodological limitations remain [1, 4, 5].

Further progress in this field necessitates large, long-term randomized trials with clear ketosis criteria and standardized protocols, as current data remain scarce, heterogeneous, and often short-term and uncontrolled [3].