Ketogenic diets and the nervous system: a scoping review of neurological outcomes from nutritional ketosis in animal studies

Bibliometric and visual analysis in the field of the ketogenic diet in relation to brain health from 2013 to 2024

Objectives

The metabolites of the ketogenic diet (KD), specifically ketone bodies (KB), are closely linked to brain health. The KD is widely used to treat epilepsy. It's also getting more attention for treating neurodegenerative disorders like Alzheimer's and Parkinson's diseases, and its effectiveness in these areas is well - recognized. This study aims to explore the research hotspots in the field of KD and brain health from 2013 to 2024, providing references and directions for future research.

Methods

This study utilized R software, VOSviewer, and CiteSpace to analyze 1,162 publications in this field from 2013 to 2024.

Results

A total of 1,162 publications were included in this study. From 2013 to 2021, there was an upward trend in the number of publications in this field, followed by a slight decline from 2021 to 2023. The United States has the highest number of publications and exhibits the most extensive collaboration with other countries, positioning it as the leading nation in this field. The journal Nutrients has the highest number of publications, while Epilepsia is the most cited journal. Key subject terms include KD, Brain, Beta-Hydroxybutyrate, KB, Metabolism, and Oxidative Stress. The primary research focuses in this field are the application of the KD and its metabolites in treating brain disorders such as epilepsy, the role and mechanisms of the KD and its metabolites in brain metabolism, and the effects of the physiological properties of KD metabolites (e.g., KB) such as antioxidative stress and neuroprotection on brain health.

Conclusion

The KD is beneficial for brain health, and its use in treating brain disorders has garnered widespread attention and recognition globally. This study provides a comprehensive and in-depth analysis of the literature in this field, offering valuable insights into the research hotspots and future directions for investigation.

Ketogenic Food Ameliorates Activity-Based Anorexia of Adult Female Mice

OBJECTIVE

Genome-wide association studies implicate metabo-psychiatric origins for anorexia nervosa (AN). There are two case reports totaling six adult females who experienced complete remission of AN following a treatment comprised of ketogenic diet (targeting metabolism) with ketamine infusions (targeting psychiatric origins), but no study has determined the efficacy of ketogenic diet, alone. We addressed this gap in knowledge, with exploration of potential molecular mechanisms, using an animal model.

METHOD

Adult C57BL6 female mice underwent 2 or 3 cycles of activity-based anorexia (ABA1, ABA2, ABA3), an animal model of AN relapse, in which AN-like maladaptive behaviors of hyperactivity and voluntary food restriction are elicited when wheel access is combined with food restriction. ABA was categorized as severe, based on weight loss ≥ 20%, food restriction-evoked increase in wheel counts > 10,000/6 h, and crouching/grimace, and compared across two groups: (1) KG, fed ketogenic food continuously (N = 25); and (2) CON, fed standard diet (N = 28).

RESULTS

86% of CON versus none of the KG were crouching with grimace during ABA1. 93% of CON versus 11% of KG lost weight severely during ABA2 (p < 0.001, 8% difference of group mean weights). Severe hyperactivity was prevalent among CON (86%) and rare for KG (4%) during ABA2 (p < 0.001 on all food-restricted days). ABA up-regulated BDNF (brain-derived neurotrophic factor) in the hippocampus of both groups but ketone body, β-hydroxybutyrate, in urine was increased only among KG.

DISCUSSION

Ketogenic diet may reduce severity of AN relapse through reduction of compulsive exercise, via mechanisms that are in addition to BDNF up-regulation and involve β-hydroxybutyrate.

1,3-butanediol administration as an alternative strategy to calorie restriction for neuroprotection - Insights into modulation of stress response in hippocampus of healthy rats

Ketogenic diet has a wide range of beneficial effects but presents practical limitations due to its low compliance, hence dietary supplements have been developed to induce ketosis without nutrient deprivation. The alcohol 1,3-butanediol (BD) is a promising molecule for its ability to induce ketosis, but its effects on brain have been investigated so far only in disease models, but never in physiological conditions. To support BD use to preserve brain health, the analysis of its activity is mandatory. Therefore, we investigated, in healthy rats, the effect of a fourteen-days BD-administration on the hippocampus, an area particularly vulnerable to oxidative and inflammatory damage. Since BD treatment has been reported to reduce energy intake, results were compared with those obtained from rats undergoing a restricted dietary regimen, isoenergetic with BD group (pair fed, PF). Reduced pro-inflammatory signaling pathways and glial activation were revealed in hippocampus of BD treated rats in comparison to control (C) and PF groups. ROS content and the extent of protein oxidative damage were lower in BD and PF groups than in C. Interestingly, higher amounts of nuclear factor erythroid 2-related factor 2 (Nrf2), decreased level of lipid hydroperoxides, lower susceptibility to oxidative insult, higher amounts of superoxide dismutase-2, glutathione reductase and glutathione peroxidase (GPx), and increased GPx activity were observed in BD animals. BD administration, but not dietary restriction, attenuated endoplasmic reticulum stress, reduced autophagic response activation, and was associated with an increase of both the neurotrophin BDNF and pre-synaptic proteins synaptophysin and synaptotagmin. Our results highlight that BD plays a neuroprotective role in healthy conditions, thus emerging as an effective strategy to support brain function without the need of implementing ketogenic nutritional interventions.

Ketone Esters Partially and Selectively Rescue Mitochondrial Bioenergetics After Acute Cervical Spinal Cord Injury in Rats: A Time-Course

Spinal cord injury (SCI) pathology and pathophysiology can be attributed to both primary physical injury and secondary injury cascades. Secondary injury cascades involve dysregulated metabolism and energetic deficits directly linked to compromised mitochondrial bioenergetics. Rescuing mitochondrial function and reducing oxidative stress are associated with neuroprotection. In this regard, ketosis after traumatic brain injury (TBI), or after SCI, improves secondary neuropathology by decreasing oxidative stress, increasing antioxidants, reducing inflammation, and improving mitochondrial bioenergetics. Here, we follow up on our previous study and have used an exogenous ketone monoester, (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KE), as an alternative to a ketogenic diet, focusing on mitochondrial function between 1 and 14 days after injury. Starting 3 h following a cervical level 5 (C5) hemi-contusion injury, animals were fed either a standard control diet (SD) or a ketone ester diet (KED) combined with KE administered orally (OKE). We found that mitochondrial function was reduced after SCI at all times post-SCI, accompanied by reduced expression of most of the components of the electron transport chain (ETC). The KE rescued some of the bioenergetic parameters 1 day after SCI when D-β-Hydroxybutyrate (BHB) concentrations were ~2 mM. Still, most of the beneficial effects were observed 14 days after injury, with BHB concentrations reaching values of 4-6 mM. To our knowledge, this is the first report to show the beneficial effects of KE in rescuing mitochondrial function after SCI and demonstrates the suitability of KE in ameliorating the metabolic dysregulation that occurs after traumatic SCI without requiring a restrictive dietary regime.

Effect of the ketogenic diet as a treatment for refractory epilepsy in children and adolescents: a systematic review of reviews

CONTEXT

Epilepsy is one of the most prevalent neurological disorders in childhood. Antiepileptic drugs are the preferred treatment. However, 30% of children continue suffering seizures. A ketogenic diet (KD) is one of the emerging alternative treatments.

OBJECTIVE

This review aims to analyze the current evidence regarding the use of a KD for the treatment of refractory epilepsy (RE) in childhood.

DATA SOURCES

A systematic review of reviews was performed, based on MEDLINE (PubMed) as at January 2021.

DATA EXTRACTION

The data extracted included the first author's last name; the year of publication; the country; the study design; the population; the diagnosis, concept, and description of KD types; and major outcome.

RESULTS

Twenty-one reviews were included, 8 with systematic methodology (2 of them included a meta-analysis) and 13 with unsystematic methodology. The main difference between the 2 types of reviews is the reproducibility of their methodology. Therefore, the results of each type of review were analyzed separately. Each type of review described 4 categories of KD: classic KD, modified Atkins diet (MAD), use of medium-chain triglycerides (MCTs), and low glycemic index treatment (LGIT). In terms of effectiveness, the considered systematic reviews reported reductions in the frequency of seizures greater than 50% in about half of the patients. Reviews without systematic methodology reported that 30%-60% of the children showed a 50% or greater reduction in seizures. The most frequently described adverse effects in the 8 systematic reviews were: vomiting (6/8), constipation (6/8), and diarrhea (6/8); and in the unsystematic reviews: vomiting and nausea (10/13), constipation (10/13), and acidosis (9/13).

CONCLUSION

KD can be an effective treatment for RE, with a more than 50% reduction in the frequency of seizures and cognitive improvement being achieved in half of the pediatric patients. The effectiveness of the various types of KD is comparable, and the KD can be adapted to the needs of the patient.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42021244142.

The early life exposome and autism risk: a role for the maternal microbiome?

Autism spectrum disorders (ASD) are highly heritable, heterogeneous neurodevelopmental disorders characterized by clinical presentation of atypical social, communicative, and repetitive behaviors. Over the past 25 years, hundreds of ASD risk genes have been identified. Many converge on key molecular pathways, from translational control to those regulating synaptic structure and function. Despite these advances, therapeutic approaches remain elusive. Emerging data unearthing the relationship between genetics, microbes, and immunity in ASD suggest an integrative physiology approach could be paramount to delivering therapeutic breakthroughs. Indeed, the advent of large-scale multi-OMIC data acquisition, analysis, and interpretation is yielding an increasingly mechanistic understanding of ASD and underlying risk factors, revealing how genetic susceptibility interacts with microbial genetics, metabolism, epigenetic (re)programming, and immunity to influence neurodevelopment and behavioral outcomes. It is now possible to foresee exciting advancements in the treatment of some forms of ASD that could markedly improve quality of life and productivity for autistic individuals. Here, we highlight recent work revealing how gene X maternal exposome interactions influence risk for ASD, with emphasis on the intrauterine environment and fetal neurodevelopment, host-microbe interactions, and the evolving therapeutic landscape for ASD.

Low-carbohydrate and ketogenic diets: a scoping review of neurological and inflammatory outcomes in human studies and their relevance to chronic pain

Dietary restriction of carbohydrate has been demonstrated to be beneficial for nervous system dysfunction in animal models and may be beneficial for human chronic pain. The purpose of this review is to assess the impact of a low-carbohydrate/ketogenic diet on the adult nervous system function and inflammatory biomarkers to inform nutritional research for chronic pain. An electronic database search was carried out in May 2021. Publications were screened for prospective research with dietary carbohydrate intake <130 g per day and duration of ≥2 weeks. Studies were categorised into those reporting adult neurological outcomes to be extracted for analysis and those reporting other adult research outcomes. Both groups were screened again for reported inflammatory biomarkers. From 1548 studies, there were 847 studies included. Sixty-four reported neurological outcomes with 83% showing improvement. Five hundred and twenty-three studies had a different research focus (metabolic n = 394, sport/performance n = 51, cancer n = 33, general n = 30, neurological with non-neuro outcomes n = 12, or gastrointestinal n = 4). The second screen identified sixty-three studies reporting on inflammatory biomarkers, with 71% reporting a reduction in inflammation. The overall results suggest a favourable outcome on the nervous system and inflammatory biomarkers from a reduction in dietary carbohydrates. Both nervous system sensitisation and inflammation occur in chronic pain, and the results from this review indicate it may be improved by low-carbohydrate nutritional therapy. More clinical trials within this population are required to build on the few human trials that have been done.

The Role of Ketogenic Diet in the Treatment of Neurological Diseases

Over a hundred years of study on the favourable effect of ketogenic diets in the treatment of epilepsy have contributed to a long-lasting discussion on its potential influence on other neurological diseases. A significant increase in the number of scientific studies in that field has been currently observed. The aim of this paper is a widespread, thorough analysis of the available scientific evidence in respect of the role of the ketogenic diet in the therapy of neurological diseases such as: epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A wide range of the mechanisms of action of the ketogenic diet has been demonstrated in neurological diseases, including, among other effects, its influence on the reduction in inflammatory conditions and the amount of reactive oxygen species (ROS), the restoration of the myelin sheath of the neurons, the formation and regeneration of mitochondria, neuronal metabolism, the provision of an alternative source of energy for neurons (ketone bodies), the reduction in glucose and insulin concentrations, the reduction in amyloid plaques, the induction of autophagy, the alleviation of microglia activation, the reduction in excessive neuronal activation, the modulation of intestinal microbiota, the expression of genes, dopamine production and the increase in glutamine conversion into GABA. The studies discussed (including randomised controlled studies), conducted in neurological patients, have stressed the effectiveness of the ketogenic diet in the treatment of epilepsy and have demonstrated its promising therapeutic potential in Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A frequent advantage of the diet was demonstrated over non-ketogenic diets (in the control groups) in the therapy of neurological diseases, with simultaneous safety and feasibility when conducting the nutritional model.

β-Hydroxybutyrate Attenuates Painful Diabetic Neuropathy via Restoration of the Aquaporin-4 Polarity in the Spinal Glymphatic System

Waste removal is essential for maintaining homeostasis and the normal function of the central nervous system (CNS). The glymphatic system based on aquaporin-4 (AQP4) water channels on the endfeet of astrocytes is recently discovered as the excretion pathway for metabolic waste products of CNS. In the CNS, α-syntrophin (SNTA1) directly or indirectly anchors AQP4 in astrocyte membranes facing blood vessels. Studies have indicated that β-hydroxybutyrate (BHB) can raise the expression of SNTA1 and thus restoring AQP4 polarity in mice models with Alzheimer’s disease. The study aims to evaluate the neuroprotective mechanism of BHB in rats with painful diabetic neuropathy (PDN). PDN rats were modeled under a high-fat and high-glucose diet with a low dose of streptozotocin. Magnetic resonance imaging (MRI) was applied to observe the clearance of contrast to indicate the functional variability of the spinal glymphatic system. Mechanical allodynia was assessed by paw withdrawal threshold. The expressions of SNTA1 and AQP4 were tested, and the polarity reversal of AQP4 protein was measured. As demonstrated, PDN rats were manifested with deceased contrast clearance of the spinal glymphatic system, enhanced mechanical allodynia, lower expression of SNTA1, higher expression of AQP4, and reversed polarity of AQP4 protein. An opposite change in the above characteristics was observed in rats being treated with BHB. This is the first study that demonstrated the neuroprotective mechanism of BHB to attenuate PDN via restoration of the AQP4 polarity in the spinal glymphatic system and provides a promising therapeutic strategy for PDN.

The Ketogenic Diet Improves Gut-Brain Axis in a Rat Model of Irritable Bowel Syndrome: Impact on 5-HT and BDNF Systems

Altered gut-brain communication can contribute to intestinal dysfunctions in the intestinal bowel syndrome. The neuroprotective high-fat, adequate-protein, low-carbohydrate ketogenic diet (KD) modulates the levels of different neurotransmitters and neurotrophins. The aim was to evaluate the effects of KD on levels of 5-HT, the receptors 5-HT_3B and 5-HT₄, the 5-HT transporter SERT, the neurotrophin BDNF, and its receptor TrkB in the colon and brain of a rat model of irritable bowel syndrome (IBS). Samples from Wistar rats exposed to maternal deprivation as newborns and then fed with a standard diet (IBS-Std) or KD (IBS-KD) for ten weeks were analyzed. As controls, unexposed rats (Ctrl-Std and Ctrl-KD) were studied. IBS-Std rats had a disordered enteric serotoninergic signaling shown by increased mucosal 5-HT content and reduced SERT, 5-HT_3B, and 5-HT₄ levels compared to controls. In the brain, these animals showed up-regulation of the BDNF receptor TrkB as a counteracting response to the stress-induced reduction of the neurotrophin. KD showed a dual effect in improving the altered 5-HT and BDNF systems. It down-regulated the increased mucosal 5-HT without affecting transporter and receptor levels. KD improved brain BDNF levels and established negative feedback, leading to a compensatory downregulation of TrkB to maintain a physiological steady state.

Experience of participants with chronic pain in a pilot randomized clinical trial using a ketogenic diet

Aim: To report the experience of chronic pain participants after a well-formulated ketogenic diet (WFKD) or whole-food diet (WFD). The quantitative outcomes for this trial have been published separately (clinical trial registration number ACTRN12620000946910). Patients & methods: The experience of 24 participants was evaluated after 12 and 24 weeks of dietary intervention using survey responses and open questions. Results & conclusion: Retention rates for the WFKD and WFD groups were 93 and 89%, respectively. Average adherence to the WFKD was 82% and to the WFD was 87%. The WFKD enjoyment was rated at 66 and 81% for the WFD group. The ease of adhering to the diet varied more widely for the WFKD group. Barriers included knowledge integration, time management, navigating social food environments and emotional attachment to eliminated foods. Facilitators included structured support and coaching, and comprehensive learning materials. The WFKD was shown to be a feasible and effective treatment option for chronic pain.

Effects of a low-carbohydrate ketogenic diet on reported pain, blood biomarkers and quality of life in patients with chronic pain: A pilot randomised clinical trial

BACKGROUND

A low-carbohydrate ketogenic diet has been reported to improve chronic pain by reducing inflammation, oxidative stress, and sensitivity within the nervous system. The main aim of this trial is to evaluate the effects of a ketogenic diet on reported pain, blood biomarkers and quality of life in patients with chronic pain.

METHODS

Participants with chronic musculoskeletal pain were recruited for a 12-week diet intervention that commenced with a 3-week run-in diet removing ultra-processed foods, followed by randomisation to either a whole-food/well-formulated ketogenic diet (WFKD) or to continue with the minimally processed whole-food diet (WFD). Outcome measures included: average pain (visual analogue scale VAS), blood biomarkers, anthropometrics, adherence, depression, anxiety, sleep, ketones, quality of life, diet satisfaction and macronutrient intake.

RESULTS

Average weekly pain improved for both groups. WFKD group VAS reduced by 17.9 ± 5.2 mm (p = 0.004) and the WFD group VAS reduced 11.0 ± 9.0 mm (p = 0.006). Both groups also reported improved quality of life (WFKD = 11.5 ± 2.8%, p = 0.001 and WFD = 11.0 ± 3.5%, p = 0.014). The WFKD group also demonstrated significant improvements in pain interference (p = 0.013), weight (p < 0.005), depression (p = 0.015), anxiety (p = 0.013), and inflammation (hsCRP) (p = 0.009). Significant average pain reduction remained at three-month follow-up for both groups (WFKD p = 0.031, WFD p = 0.011).

CONCLUSION

The implementation of a whole-food diet that restricts ultra-processed foods is a valid pain management tool, however a low-carbohydrate ketogenic diets may have potentially greater pain reduction, weight loss and mood improvements.