Physiological roles of ketone bodies as substrates and signals in mammalian tissues

Quantification of Total Ketone Bodies in Biological Matrices Using Stable Isotope-Labeled Internal Standards and RP-UHPLC-MS/MS

Acetoacetate (AcAc) and D-beta-hydroxybutyrate (D-βOHB), the two major ketone bodies found in circulation, are linked to multiple physiological and pathophysiological states. Therefore, analytical methodologies surrounding the quantification of total ketone body (TKB) concentrations in biological matrices are paramount. Traditional methods to quantify TKBs relied on indirect spectrophotometric assays with narrow dynamic ranges, which have been significantly improved upon by modern mass spectrometry (MS)-based approaches. However, the lack of stable isotope-labeled internal standards (ISs) for AcAc and the need to distinguish D-βOHB from its closely related structural and enantiomeric isomers pose significant obstacles. Here, we provide a protocol to synthesize and quantify a [13C] stable isotope-labeled IS for AcAc, which, in conjunction with a commercially available [2H] stable isotope-labeled IS for βOHB, allows TKBs to be measured across multiple biological matrices. This rapid (7 min) analysis employs reverse phase ultra-high performance liquid chromatography (RP-UHPLC) coupled to tandem MS (MS/MS) to distinguish βOHB from three structural isomers using parallel reaction monitoring (PRM), providing excellent specificity and selectivity. Finally, a method is provided that distinguishes D-βOHB from L-βOHB using a simple one-step derivatization to produce the corresponding diastereomers, which can be chromatographically resolved using the same rapid RP-UHPLC separation with new PRM transitions. In summary, this method provides a rigorous analytical pipeline for the analysis of TKBs in biological matrices via leveraging two authentic stable isotope-labeled ISs and RP-UHPLC-MS/MS.

International society of sports nutrition position stand: ketogenic diets

POSITION STATEMENT

The International Society of Sports Nutrition (ISSN) provides an objective and critical review of the use of a ketogenic diet in healthy exercising adults, with a focus on exercise performance and body composition. However, this review does not address the use of exogenous ketone supplements. The following points summarize the position of the ISSN.

1. A ketogenic diet induces a state of nutritional ketosis, which is generally defined as serum ketone levels above 0.5 mM. While many factors can impact what amount of daily carbohydrate intake will result in these levels, a broad guideline is a daily dietary carbohydrate intake of less than 50 grams per day.

2. Nutritional ketosis achieved through carbohydrate restriction and a high dietary fat intake is not intrinsically harmful and should not be confused with ketoacidosis, a life-threatening condition most commonly seen in clinical populations and metabolic dysregulation.

3. A ketogenic diet has largely neutral or detrimental effects on athletic performance compared to a diet higher in carbohydrates and lower in fat, despite achieving significantly elevated levels of fat oxidation during exercise (~1.5 g/min).

4. The endurance effects of a ketogenic diet may be influenced by both training status and duration of the dietary intervention, but further research is necessary to elucidate these possibilities. All studies involving elite athletes showed a performance decrement from a ketogenic diet, all lasting six weeks or less. Of the two studies lasting more than six weeks, only one reported a statistically significant benefit of a ketogenic diet.

5. A ketogenic diet tends to have similar effects on maximal strength or strength gains from a resistance training program compared to a diet higher in carbohydrates. However, a minority of studies show superior effects of non-ketogenic comparators.

6. When compared to a diet higher in carbohydrates and lower in fat, a ketogenic diet may cause greater losses in body weight, fat mass, and fat-free mass, but may also heighten losses of lean tissue. However, this is likely due to differences in calorie and protein intake, as well as shifts in fluid balance.

7. There is insufficient evidence to determine if a ketogenic diet affects males and females differently. However, there is a strong mechanistic basis for sex differences to exist in response to a ketogenic diet.

Nutritional Considerations During Major Weight Loss Therapy: Focus on Optimal Protein and a Low-Carbohydrate Dietary Pattern

PURPOSE OF REVIEW

Considering the high prevalence of obesity and related metabolic impairments in the population, the unique role nutrition has in weight loss, reversing metabolic disorders, and maintaining health cannot be overstated. Normal weight and well-being are compatible with varying dietary patterns, but for the last half century there has been a strong emphasis on low-fat, low-saturated fat, high-carbohydrate based approaches. Whereas low-fat dietary patterns can be effective for a subset of individuals, we now have a population where the vast majority of adults have excess adiposity and some degree of metabolic impairment. We are also entering a new era with greater access to bariatric surgery and approval of anti-obesity medications (glucagon-like peptide-1 analogues) that produce substantial weight loss for many people, but there are concerns about disproportionate loss of lean mass and nutritional deficiencies.

RECENT FINDINGS

No matter the approach used to achieve major weight loss, careful attention to nutritional considerations is necessary. Here, we examine the recent findings regarding the importance of adequate protein to maintain lean mass, the rationale and evidence supporting low-carbohydrate and ketogenic dietary patterns, and the potential benefits of including exercise training in the context of major weight loss. While losing and sustaining weight loss has proven challenging, we are optimistic that application of emerging nutrition science, particularly personalized well-formulated low-carbohydrate dietary patterns that contain adequate protein (1.2 to 2.0 g per kilogram reference weight) and achieve the beneficial metabolic state of euketonemia (circulating ketones 0.5 to 5 mM), is a promising path for many individuals with excess adiposity.

Signals of energy availability in sleep: consequences of a fat-based metabolism

Humans can flexibly switch between two primary metabolic modes, usually distinguished by whether substrate supply from glucose can meet energy demands or not. However, it is often overlooked that when glucose use is limited, the remainder of energy needs may still be met more or less effectively with fat and ketone bodies. Hence a fat-based metabolism marked by ketosis is often conflated with starvation and contexts of inadequate energy (including at the cellular level), even when energy itself is in ample supply. Sleep and satiation are regulated by common pathways reflecting energy metabolism. A conceptual analysis that distinguishes signals of inadequate energy in a glucose-dominant metabolism from signals of a fat-based metabolism that may well be energy sufficient allows a reexamination of experimental results in the study of sleep that may shed light on species differences and explain why ketogenic diets have beneficial effects simultaneously in the brain and the periphery. It may also help to distinguish clinically when a failure of a ketogenic diet to resolve symptoms is due to inadequate energy rather than the metabolic state itself.

Ketogenic Interventions in Autosomal Dominant Polycystic Kidney Disease: A Comprehensive Review of Current Evidence

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a genetic disorder characterized by the development and enlargement of multiple kidney cysts, leading to progressive kidney function decline. To date, Tolvaptan, the only approved treatment for this condition, is able to slow down the loss of annual kidney function without stopping the progression of the disease. Furthermore, this therapy is approved only for patients with rapid disease progression and its compliance is problematic because of the drug's impact on quality of life. The recent literature suggests that cystic cells are subject to several metabolic dysregulations, particularly in the glucose pathway, and mitochondrial abnormalities, leading to decreased oxidative phosphorylation and impaired fatty acid oxidation. This finding paved the way for new lines of research targeting potential therapeutic interventions for ADPKD. In particular, this review highlights the latest studies on the use of ketosis, through ketogenic dietary interventions (daily calorie restriction, intermittent fasting, time-restricted feeding, ketogenic diets, and exogenous ketosis), as a potential strategy for patients with ADPKD, and the possible involvement of microbiota in the ketogenic interventions' effect.

Ketone monoester plus high-dose glucose supplementation before exercise does not affect immediate post-exercise erythropoietin concentrations versus glucose alone

The objective of this study was to examine the effect of consuming ketone monoester plus a high dose of carbohydrate from glucose (KE + CHO) on the change in erythropoietin (EPO) concentrations during load carriage exercise compared with carbohydrate (CHO) alone. Using a randomized, crossover design, 12 males consumed KE + CHO (573 mg KE/kg body mass, 110 g glucose) or CHO (110 g glucose) 30 min before 4 miles of self-paced treadmill exercise (KE + CHO:51 ± 13%, CHO: 52 ± 12% V̇O2peak) wearing a weighted vest (30% body mass; 25 ± 3 kg). Blood samples for analysis were obtained under resting fasted conditions before (Baseline) consuming the KE + CHO or CHO supplement and immediately after exercise (Post). βHB increased (p < 0.05) from Baseline to Post in KE + CHO, with no change in CHO. Glucose and glycerol increased (p < 0.05) from Baseline to Post in CHO, with no effect of time in KE + CHO. Insulin and lactate increased (p < 0.05) from Baseline to Post independent of treatment. EPO increased (p < 0.05) from Baseline to Post in KE + CHO and CHO with no difference between treatments. Although KE + CHO altered βHB, glucose, and glycerol concentrations, results from this study suggest that KE + CHO supplementation before load carriage exercise does not enhance immediate post-exercise increases in EPO compared with CHO alone.

Specific regulation of epigenome landscape by metabolic enzymes and metabolites

Metabolism includes anabolism and catabolism, which play an essential role in many biological processes. Chromatin modifications are post-translational modifications of histones and nucleic acids that play important roles in regulating chromatin-associated processes such as gene transcription. There is a tight connection between metabolism and chromatin modifications. Many metabolic enzymes and metabolites coordinate cellular activities with alterations in nutrient availability by regulating gene expression through epigenetic mechanisms such as DNA methylation and histone modifications. The dysregulation of gene expression by metabolism and epigenetic modifications may lead to diseases such as diabetes and cancer. Recent studies reveal that metabolic enzymes and metabolites specifically regulate chromatin modifications, including modification types, modification residues and chromatin regions. This specific regulation has been implicated in the development of human diseases, yet the underlying mechanisms are only beginning to be uncovered. In this review, we summarise recent studies of the molecular mechanisms underlying the metabolic regulation of histone and DNA modifications and discuss how they contribute to pathogenesis. We also describe recent developments in technologies used to address the key questions in this field. We hope this will inspire further in-depth investigations of the specific regulatory mechanisms involved, and most importantly will shed lights on the development of more effective disease therapies.

Energy supply during nocturnal endurance flight of migrant birds: effect of energy stores and flight behaviour

BACKGROUND

Migrating birds fly non-stop for hours or even for days. They rely mainly on fat as fuel complemented by a certain amount of protein. Studies on homing pigeons and birds flying in a wind-tunnel suggest that the shares of fat and protein on total energy expenditure vary with flight duration and body fat stores. Also, flight behaviour, such as descending flight, is expected to affect metabolism. However, studies on free flying migrant birds under natural conditions are lacking.

METHODS

On a Swiss Alpine pass, we caught three species of nocturnal migrant passerines out of their natural migratory flight. Since most night migrants start soon after dusk, we used time since dusk as a measure of flight duration. We used plasma concentrations of metabolites of the fat, protein, and carbohydrate metabolism as indicators of relative fuel use. We used flight altitudes of birds tracked with radar and with atmospheric pressure loggers to characterize flight behaviour.

RESULTS

The indicators of fat catabolism (triglycerides, very low-density lipoproteins, glycerol) were positively correlated with body energy stores, supporting earlier findings that birds with high fat stores have a higher fat catabolism. As expected, plasma levels of triglycerides, very low-density lipoproteins, glycerol and ß-hydroxy-butyrate increased at the beginning of the night, indicating that nocturnal migrants increased their fat metabolism directly after take-off. Surprisingly, fat catabolism as well as glucose levels decreased in the second half of the night. Data from radar observations showed that the number of birds aloft, their mean height above ground and vertical flight speed decreased after midnight. Together with the findings from atmospheric pressure-loggers put on three species, this shows that nocturnal migrants migrating over continental Europe descend slowly during about 1.5 h before final landfall at night, which results in 11-30% energy savings according to current flight models.

CONCLUSIONS

We suggest that this slow descent reduces energy demands to an extent which is noticeable in the plasma concentration of lipid, protein, and carbohydrate metabolites. The slow descent may facilitate the search for a suitable resting habitat and serve to refill glycogen stores needed for foraging and predator escape when landed.

A novel hepatocyte ketone production assay to help the selection of nutrients for the ketogenic diet treatment of epilepsy

The classic ketogenic diet is an effective treatment option for drug-resistant epilepsy, but its high fat content challenges patient compliance. Optimizing liver ketone production guided by a method comparing substrates for their ketogenic potential may help to reduce the fat content of the diet without loss in ketosis induction. Here, we present a liver cell assay measuring the β-hydroxybutyrate (βHB) yield from fatty acid substrates. Even chain albumin-conjugated fatty acids comprising between 4 and 18 carbon atoms showed a sigmoidal concentration-βHB response curve (CRC) whereas acetate and omega-3 PUFAs produced no CRC. While CRCs were not distinguished by their half-maximal effective concentration (EC50), they differed by maximum response, which related inversely to the carbon chain length and was highest for butyrate. The assay also suitably assessed the βHB yield from fatty acid blends detecting shifts in maximum response from exchanging medium chain fatty acids for long chain fatty acids. The assay further detected a dual role for butyrate and hexanoic acid as ketogenic substrate at high concentration and ketogenic enhancer at low concentration, augmenting the βHB yield from oleic acid and a fatty acid blend. The assay also found propionate to inhibit ketogenesis from oleic acid and a fatty acid blend at low physiological concentration. Although the in vitro assay shows promise as a tool to optimize the ketogenic yield of a fat blend, its predictive value requires human validation.

The dentate gyrus differentially metabolizes glucose and alternative fuels during rest and stimulation

The metabolic demands of neuronal activity are both temporally and spatially dynamic, and neurons are particularly sensitive to disruptions in fuel and oxygen supply. Glucose is considered an obligate fuel for supporting brain metabolism. Although alternative fuels are often available, the extent of their contribution to central carbon metabolism remains debated. Differential fuel metabolism likely depends on cell type, location, and activity state, complicating its study. While biosensors provide excellent spatial and temporal information, they are limited to observations of only a few metabolites. On the other hand, mass spectrometry is rich in chemical information, but traditionally relies on cell culture or homogenized tissue samples. Here, we use mass spectrometry imaging (MALDI-MSI) to focus on the fuel metabolism of the dentate granule cell (DGC) layer in murine hippocampal slices. Using stable isotopes, we explore labeling dynamics at baseline, as well as in response to brief stimulation or fuel competition. We find that at rest, glucose is the predominant fuel metabolized through glycolysis, with little to no measurable contribution from glycerol or fructose. However, lactate/pyruvate, β-hydroxybutyrate (βHB), octanoate, and glutamine can contribute to TCA metabolism to varying degrees. In response to brief depolarization with 50 mM KCl, glucose metabolism was preferentially increased relative to the metabolism of alternative fuels. With an increased supply of alternative fuels, both lactate/pyruvate and βHB can outcompete glucose for TCA cycle entry. While lactate/pyruvate modestly reduced glucose contribution to glycolysis, βHB caused little change in glycolysis. This approach achieves broad metabolite coverage from a spatially defined region of physiological tissue, in which metabolic states are rapidly preserved following experimental manipulation. Using this powerful methodology, we investigated metabolism within the dentate gyrus not only at rest, but also in response to the energetic demand of activation, and in states of fuel competition.

Effect of exogenous and endogenous ketones on respiratory exchange ratio and glucose metabolism in healthy subjects

This study examined the effect of exogenous ketone bodies (KB) on oxygen consumption (V̇o2), carbon dioxide production (V̇co2), and glucose metabolism. The data were compared with the effects of endogenous ketonemia during both, a ketogenic diet or fasting. Eight healthy individuals [24.1 ± 2.5 yr, body mass index (BMI) 24.3 ± 3.1 kg/m2] participated in a crossover intervention study and were studied in a whole-room indirect calorimeter (WRIC) to assess macronutrient oxidation following four 24-h interventions: isocaloric controlled mixed diet (ISO), ISO supplemented with ketone salts (38.7 g of β-hydroxybutyrate/day, EXO), isocaloric ketogenic diet (KETO), and total fasting (FAST). A physical activity level of 1.65 was obtained. In addition to plasma KB, 24-h C-peptide and KB excretion rates in the urine and postprandial glucose and insulin levels were measured. Although 24-h KB excretion increased in response to KETO and FAST, there was a modest increase in response to EXO only (P < 0.05). When compared with ISO, V̇o2 significantly increased in KETO (P < 0.01) and EXO (P < 0.001), whereas there was no difference in FAST. V̇co2 increased in EXO but decreased in KETO (both P < 0.01) and FAST (P < 0.001), resulting in 24-h respiratory exchange ratios (RER) of 0.828 ± 0.024 (ISO) and 0.811 ± 0.024 (EXO) (P < 0.05). In response to EXO there were no differences in basal and postprandial glucose and insulin levels, as well as in insulin sensitivity. When compared with ISO, EXO, and KETO, FAST increased homeostatic model assessment β-cell function (HOMA-B) (all P < 0.05). In conclusion, at energy balance exogenous ketone salts decreased respiratory exchange ratio without affecting glucose tolerance.NEW & NOTEWORTHY Our findings revealed that during isocaloric nutrition, additional exogenous ketone salts increased V̇o2 and V̇co2 while lowering the respiratory exchange ratio (RER). Ketone salts had no effect on postprandial glucose metabolism.

Relationship between serum β-hydroxybutyrate and hepatic fatty acid oxidation in individuals with obesity and NAFLD

Nonalcoholic fatty liver disease (NAFLD) is characterized by excess lipid accumulation that can progress to inflammation (nonalcoholic steatohepatitis, NASH), and fibrosis. Serum β-hydroxybutyrate (β-HB), a product of the ketogenic pathway, is commonly used as a surrogate marker for hepatic fatty acid oxidation (FAO). However, it remains uncertain whether this relationship holds true in the context of NAFLD in humans. We compared fasting serum β-HB levels with direct measurement of liver mitochondrial palmitate oxidation in humans stratified based on NAFLD severity (n = 142). Patients were stratified based on NAFLD activity score (NAS): NAS = 0 (no disease), NAS = 1-2 (mild), NAS = 3-4 (moderate), and NAS ≥ 5 (advanced). Moderate and advanced NAFLD is associated with reductions in liver 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), serum β-HB, but not 3-hydroxy-3-methylglutaryl-CoA lyase (HMGCL) mRNA, relative to no disease. Worsening liver mitochondrial complete palmitate oxidation corresponded with lower HMGCS2 mRNA but not total (complete + incomplete) palmitate oxidation. Interestingly, we found that liver HMGCS2 mRNA and serum β-HB correlated with liver mitochondrial β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity and CPT1A mRNA. Also, lower mitochondrial mass and markers of mitochondrial turnover positively correlated with lower HMGCS2 in the liver. These data suggest that liver ketogenesis and FAO occur at comparable rates in individuals with NAFLD. Our findings support the utility of serum β-HB to serve as a marker of liver injury and hepatic FAO in the context of NAFLD.NEW & NOTEWORTHY Serum β-hydroxybutyrate (β-HB) is frequently utilized as a surrogate marker for hepatic fatty acid oxidation; however, few studies have investigated this relationship during states of liver disease. We found that the progression of nonalcoholic fatty liver disease (NAFLD) is associated with reductions in circulating β-HB and liver 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2). As well, decreased rates of hepatic fatty acid oxidation correlated with liver HMGCS2 mRNA and serum β-HB. Our work supports serum β-HB as a potential marker for hepatic fatty acid oxidation and liver injury during NAFLD.

Protein Post-Translational Modifications Based on Proteomics: A Potential Regulatory Role in Animal Science

Genomic studies in animal breeding have provided a wide range of references; however, it is important to note that genes and mRNA alone do not fully capture the complexity of living organisms. Protein post-translational modification, which involves covalent modifications regulated by genetic and environmental factors, serves as a fundamental epigenetic mechanism that modulates protein structure, activity, and function. In this review, we comprehensively summarize various phosphorylation and acylation modifications on metabolic enzymes relevant to energy metabolism in animals, including acetylation, succinylation, crotonylation, β-hydroxybutylation, acetoacetylation, and lactylation. It is worth noting that research on animal energy metabolism and modification regulation lags behind the demands for growth and development in animal breeding compared to human studies. Therefore, this review provides a novel research perspective by exploring unreported types of modifications in livestock based on relevant findings from human or animal models.

Ketone Monoester Followed by Carbohydrate Ingestion after Glycogen-Lowering Exercise Does Not Improve Subsequent Endurance Cycle Time Trial Performance

Relative to carbohydrate (CHO) alone, exogenous ketones followed by CHO supplementation during recovery from glycogen-lowering exercise have been shown to increase muscle glycogen resynthesis. However, whether this strategy improves subsequent exercise performance is unknown. The objective of this study was to assess the efficacy of ketone monoester (KME) followed by CHO ingestion after glycogen-lowering exercise on subsequent 20 km (TT20km) and 5 km (TT5km) best-effort time trials. Nine recreationally active men (175.6 ± 5.3 cm, 72.9 ± 7.7 kg, 28 ± 5 y, 12.2 ± 3.2% body fat, VO2max = 56.2 ± 5.8 mL· kg BM-1·min-1; mean ± SD) completed a glycogen-lowering exercise session, followed by 4 h of recovery and subsequent TT20km and TT5km. During the first 2 h of recovery, participants ingested either KME (25 g) followed by CHO at a rate of 1.2 g·kg-1·h-1 (KME + CHO) or an iso-energetic placebo (dextrose) followed by CHO (PLAC + CHO). Blood metabolites during recovery and performance during the subsequent two-time trials were measured. In comparison to PLAC + CHO, KME + CHO displayed greater (p < 0.05) blood beta-hydroxybutyrate concentration during the first 2 h, lower (p < 0.05) blood glucose concentrations at 30 and 60 min, as well as greater (p < 0.05) blood insulin concentration 2 h following ingestion. However, no treatment differences (p > 0.05) in power output nor time to complete either time trial were observed vs. PLAC + CHO. These data indicate that the metabolic changes induced by KME + CHO ingestion following glycogen-lowering exercise are insufficient to enhance subsequent endurance time trial performance.

Prostaglandin D2 synthase controls Schwann cells metabolism

We previously reported that in the absence of Prostaglandin D2 synthase (L-PGDS) peripheral nerves are hypomyelinated in development and that with aging they present aberrant myelin sheaths. We now demonstrate that L-PGDS expressed in Schwann cells is part of a coordinated program aiming at preserving myelin integrity. In vivo and in vitro lipidomic, metabolomic and transcriptomic analyses confirmed that myelin lipids composition, Schwann cells energetic metabolism and key enzymes controlling these processes are altered in the absence of L-PGDS. Moreover, Schwann cells undergo a metabolic rewiring and turn to acetate as the main energetic source. Further, they produce ketone bodies to ensure glial cell and neuronal survival. Importantly, we demonstrate that all these changes correlate with morphological myelin alterations and describe the first physiological pathway implicated in preserving PNS myelin. Collectively, we posit that myelin lipids serve as a reservoir to provide ketone bodies, which together with acetate represent the adaptive substrates Schwann cells can rely on to sustain the axo-glial unit and preserve the integrity of the PNS.

A miniaturized culture platform for control of the metabolic environment

The heart is a metabolic "omnivore" and adjusts its energy source depending on the circulating metabolites. Human cardiac organoids, a three-dimensional in vitro model of the heart wall, are a useful tool to study cardiac physiology and pathology. However, cardiac tissue naturally experiences shear stress and nutrient fluctuations via blood flow in vivo, whilst in vitro models are conventionally cultivated in a static medium. This necessitates the regular refreshing of culture media, which creates acute cellular disturbances and large metabolic fluxes. To culture human cardiac organoids in a more physiological manner, we have developed a perfused bioreactor for cultures in a 96-well plate format. The designed bioreactor is easy to fabricate using a common culture plate and a 3D printer. Its open system allows for the use of traditional molecular biology techniques, prevents flow blockage issues, and provides easy access for sampling and cell assays. We hypothesized that a perfused culture would create more stable environment improving cardiac function and maturation. We found that lactate is rapidly produced by human cardiac organoids, resulting in large fluctuations in this metabolite under static culture. Despite this, neither medium perfusion in bioreactor culture nor lactate supplementation improved cardiac function or maturation. In fact, RNA sequencing revealed little change across the transcriptome. This demonstrates that cardiac organoids are robust in response to fluctuating environmental conditions under normal physiological conditions. Together, we provide a framework for establishing an easily accessible perfusion system that can be adapted to a range of miniaturized cell culture systems.

Levels of Circulating Ketone Bodies in Patients Undergoing Cardiac Surgery on Cardiopulmonary Bypass

Ketone bodies (KBs) are energy-efficient substrates utilized by the heart depending on its metabolic demand and substrate availability. Levels of circulating KBs have been shown to be elevated in acute and chronic cardiovascular disease and are associated with severity of disease in patients with heart failure and functional outcome after myocardial infarction. To investigate whether this pattern similarly applies to patients undergoing cardiac surgery involving cardiopulmonary bypass (CPB), we analysed prospectively collected pre- and postoperative blood samples from 192 cardiac surgery patients and compared levels and perioperative changes in total KBs with Troponin T as a marker of myocardial cell injury. We explored the association of patient characteristics and comorbidities for each of the two biomarkers separately and comparatively. Median levels of KBs decreased significantly over the perioperative period and inversely correlated with changes observed for Troponin T. Associations of patient characteristics with ketone body perioperative course showed notable differences compared to Troponin T, possibly highlighting factors acting as a "driver" for the change in the respective biomarker. We found an inverse correlation between perioperative change in ketone body levels and changes in troponin, indicating a marked decrease in ketone body concentrations in patients exhibiting greater myocardial cell injury. Further investigations aimed at better understanding the role of KBs on perioperative changes are warranted.

The therapeutic potential of ketones in cardiometabolic disease: impact on heart and skeletal muscle

β-Hydroxybutyrate (βOHB) is the major ketone in the body, and it is recognized as a metabolic energy source and an important signaling molecule. While ketone oxidation is essential in the brain during prolonged fasting/starvation, other organs such as skeletal muscle and the heart also use ketones as metabolic substrates. Additionally, βOHB-mediated molecular signaling events occur in heart and skeletal muscle cells, and via metabolism and/or signaling, ketones may contribute to optimal skeletal muscle health and cardiac function. Of importance, when the use of ketones for ATP production and/or as signaling molecules becomes disturbed in the presence of underlying obesity, type 2 diabetes, and/or cardiovascular diseases, these changes may contribute to cardiometabolic disease. As a result of these disturbances in cardiometabolic disease, multiple approaches have been used to elevate circulating ketones with the goal of optimizing either ketone metabolism or ketone-mediated signaling. These approaches have produced significant improvements in heart and skeletal muscle during cardiometabolic disease with a wide range of benefits that include improved metabolism, weight loss, better glycemic control, improved cardiac and vascular function, as well as reduced inflammation and oxidative stress. Herein, we present the evidence that indicates that ketone therapy could be used as an approach to help treat cardiometabolic diseases by targeting cardiac and skeletal muscles.

Cardiac Metabolism, Reprogramming, and Diseases

Cardiovascular diseases (CVD) account for the largest bulk of deaths worldwide, posing a massive burden on societies and the global healthcare system. Besides, the incidence and prevalence of these diseases are on the rise, demanding imminent action to revert this trend. Cardiovascular pathogenesis harbors a variety of molecular and cellular mechanisms among which dysregulated metabolism is of significant importance and may even proceed other mechanisms. The healthy heart metabolism primarily relies on fatty acids for the ultimate production of energy through oxidative phosphorylation in mitochondria. Other metabolites such as glucose, amino acids, and ketone bodies come next. Under pathological conditions, there is a shift in metabolic pathways and the preference of metabolites, termed metabolic remodeling or reprogramming. In this review, we aim to summarize cardiovascular metabolism and remodeling in different subsets of CVD to come up with a new paradigm for understanding and treatment of these diseases.

Subcutaneous deuterated substrate administration in mice: An alternative to tail vein infusion

PURPOSE

Tail-vein catheterization and subsequent in-magnet infusion is a common route of administration of deuterium (2 H)-labeled substrates in small-animal deuterium (D) MR studies. With mice, because of the tail vein's small diameter, this procedure is challenging. It requires considerable personnel training and practice, is prone to failure, and may preclude serial studies. Motivated by the need for an alternative, the time courses for common small-molecule deuterated substrates and downstream metabolites in brain following subcutaneous infusion were determined in mice and are presented herein.

METHODS

Three 2 H-labeled substrates-[6,6-2 H2 ]glucose, [2 H3 ]acetate, and [3,4,4,4-2 H4 ]beta-hydroxybutyrate-and 2 H2 O were administered to mice in-magnet via subcutaneous catheter. Brain time courses of the substrates and downstream metabolites (and semi-heavy water) were determined via single-voxel DMRS.

RESULTS

Subcutaneous catheter placement and substrate administration was readily accomplished with limited personnel training. Substrates reached pseudo-steady state in brain within ∼30-40 min of bolus infusion. Time constants characterizing the appearance in brain of deuterated substrates or semi-heavy water following 2 H2 O administration were similar (∼15 min).

CONCLUSION

Administration of deuterated substrates via subcutaneous catheter for in vivo DMRS experiments with mice is robust, requires limited personnel training, and enables substantial dosing. It is suitable for metabolic studies where pseudo-steady state substrate administration/accumulation is sufficient. It is particularly advantageous for serial longitudinal studies over an extended period because it avoids inevitable damage to the tail vein following multiple catheterizations.

Common and divergent molecular mechanisms of fasting and ketogenic diets

Intermittent short-term fasting (ISTF) and ketogenic diets (KDs) exert overlapping but not identical effects on cell metabolism, function, and resilience. Whereas health benefits of KD are largely mediated by the ketone bodies (KBs), ISTF engages additional adaptive physiological responses. KDs act mainly through inhibition of histone deacetylases (HDACs), reduction of oxidative stress, improvement of mitochondria efficiency, and control of inflammation. Mechanisms of action of ISTF include stimulation of autophagy, increased insulin and leptin sensitivity, activation of AMP-activated protein kinase (AMPK), inhibition of the mechanistic target of rapamycin (mTOR) pathway, bolstering mitochondrial resilience, and suppression of oxidative stress and inflammation. Frequent switching between ketogenic and nonketogenic states may optimize health by increasing stress resistance, while also enhancing cell plasticity and functionality.

Metabolic regulation in erythroid differentiation by systemic ketogenesis in fasted mice

Erythroid terminal differentiation and maturation depend on an enormous energy supply. During periods of fasting, ketone bodies from the liver are transported into circulation and utilized as crucial fuel for peripheral tissues. However, the effects of fasting or ketogenesis on erythroid behavior remain unknown. Here, we generated a mouse model with insufficient ketogenesis by conditionally knocking out the gene encoding the hepatocyte-specific ketogenic enzyme hydroxymethylglutary-CoA synthase 2 (Hmgcs2 KO). Intriguingly, erythroid maturation was enhanced with boosted fatty acid synthesis in the bone marrow of a hepatic Hmgcs2 KO mouse under fasting conditions, suggesting that systemic ketogenesis has a profound effect on erythropoiesis. Moreover, we observed significantly activated fatty acid synthesis and mevalonate pathways along with reduced histone acetylation in immature erythrocytes under a less systemic ketogenesis condition. Our findings revealed a new insight into erythroid differentiation, in which metabolic homeostasis and histone acetylation mediated by ketone bodies are essential factors in adaptation toward nutrient deprivation and stressed erythropoiesis.

Beta-Hydroxybutyrate Augments Oxaliplatin-Induced Cytotoxicity by Altering Energy Metabolism in Colorectal Cancer Organoids

Deregulation of cellular metabolism has recently emerged as a notable cancer characteristic. This reprogramming of key metabolic pathways supports tumor growth. Targeting cancer metabolism demonstrates the potential for managing colorectal cancer. Beta-hydroxybutyrate (BOHB) acts as an acetyl-CoA source for the tricarboxylic acid (TCA) cycle, possibly redirecting energy metabolic pathways towards the TCA cycle that could enhance sensitivity to oxaliplatin, through the generation of reactive oxygen species (ROS). This study explores the potential of BOHB to enhance oxaliplatin's cytotoxic effect by altering the energy metabolism in colorectal cancer. The study employed advanced in vitro organoid technology, which successfully emulates in vivo physiology. The combination treatment efficacy of BOHB and oxaliplatin was evaluated via cell viability assay. The levels of key proteins involved in energy metabolism, apoptotic pathways, DNA damage markers, and histone acetylation were analyzed via Western Blot. ROS levels were evaluated via flow cytometer. Non-toxic doses of BOHB with oxaliplatin significantly amplified cytotoxicity in colorectal cancer organoids. Treatment with BOHB and/or melatonin resulted in significantly decreased lactate dehydrogenase A and increased mitochondrial carrier protein 2 levels, indicating inhibited aerobic glycolysis and an increased oxidative phosphorylation rate. This metabolic shift induced apoptotic cell death mediated by oxaliplatin, owing to high levels of ROS. Melatonin counteracted this effect by protecting cancer cells from high oxidative stress conditions. BOHB may enhance the efficacy of chemotherapeutics with a similar mechanism of action to oxaliplatin in colorectal cancer treatment. These innovative combinations could improve treatment outcomes for colorectal cancer patients.

Insulin resistance and metabolic flexibility as drivers of liver and cardiac disease in T2DM

Metabolic flexibility refers to the ability of tissues to adapt their use of energy sources according to substrate availability and energy demands. This review aims to disentangle the emerging mechanisms through which altered metabolic flexibility and insulin resistance promote NAFLD and heart disease progression. Insulin resistance and metabolic inflexibility are central drivers of hepatic and cardiac diseases in individuals with type 2 diabetes. Both play a critical role in the complex interaction between glucose and lipid metabolism. Disruption of metabolic flexibility results in hyperglycemia and abnormal lipid metabolism, leading to increased accumulation of fat in the liver, contributing to the development and progression of NAFLD. Similarly, insulin resistance affects cardiac glucose metabolism, leading to altered utilization of energy substrates and impaired cardiac function, and influence cardiac lipid metabolism, further exacerbating the progression of heart failure. Regular physical activity promotes metabolic flexibility by increasing energy expenditure and enabling efficient switching between different energy substrates. On the contrary, weight loss achieved through calorie restriction ameliorates insulin sensitivity without improving flexibility. Strategies that mimic the effects of physical exercise, such as pharmacological interventions or targeted lifestyle modifications, show promise in effectively treating both diabetes and NAFLD, finally reducing the risk of advanced liver disease.

The Impact of Ketone Body Metabolism on Mitochondrial Function and Cardiovascular Diseases

Ketone bodies, consisting of beta-hydroxybutyrate, acetoacetate, and acetone, are metabolic byproducts known as energy substrates during fasting. Recent advancements have shed light on the multifaceted effects of ketone body metabolism, which led to increased interest in therapeutic interventions aimed at elevating ketone body levels. However, excessive elevation of ketone body concentration can lead to ketoacidosis, which may have fatal consequences. Therefore, in this review, we aimed to focus on the latest insights on ketone body metabolism, particularly emphasizing its association with mitochondria as the primary site of interaction. Given the distinct separation between ketone body synthesis and breakdown pathways, we provide an overview of each metabolic pathway. Additionally, we discuss the relevance of ketone bodies to conditions such as nonalcoholic fatty liver disease or nonalcoholic steatohepatitis and cardiovascular diseases. Moreover, we explore the utilization of ketone body metabolism, including dietary interventions, in the context of aging, where mitochondrial dysfunction plays a crucial role. Through this review, we aim to present a comprehensive understanding of ketone body metabolism and its intricate relationship with mitochondrial function, spanning the potential implications in various health conditions and the aging process.

Hepatic conversion of acetyl-CoA to acetate plays crucial roles in energy stress

Accumulating evidence indicates that acetate is increased under energy stress conditions such as those that occur in diabetes mellitus and prolonged starvation. However, how and where acetate is produced and the nature of its biological significance are largely unknown. We observed overproduction of acetate to concentrations comparable to those of ketone bodies in patients and mice with diabetes or starvation. Mechanistically, ACOT12 and ACOT8 are dramatically upregulated in the liver to convert free fatty acid-derived acetyl-CoA to acetate and CoA. This conversion not only provides a large amount of acetate, which preferentially fuels the brain rather than muscle, but also recycles CoA, which is required for sustained fatty acid oxidation and ketogenesis. We suggest that acetate is an emerging novel 'ketone body' that may be used as a parameter to evaluate the progression of energy stress.

High-fat ketogenic diets and ketone monoester supplements differentially affect substrate metabolism during aerobic exercise

Chronically adhering to high-fat ketogenic diets or consuming ketone monoester supplements elicits ketosis. Resulting changes in substrate metabolism appear to be drastically different between ketogenic diets and ketone supplements. Consuming a ketogenic diet increases fatty acid oxidation with concomitant decreases in endogenous carbohydrate oxidation. Increased fat oxidation eventually results in an accumulation of circulating ketone bodies, which are metabolites of fatty acids that serve as an alternative source of fuel. Conversely, consuming ketone monoester supplements rapidly increases circulating ketone body concentrations that typically exceed those achieved by adhering to ketogenic diets. Rapid increases in ketone body concentrations with ketone monoester supplementation elicit a negative feedback inhibition that reduces fatty acid mobilization during aerobic exercise. Supplement-derived ketosis appears to have minimal impact on sparing of muscle glycogen or minimizing of carbohydrate oxidation during aerobic exercise. This review will discuss the substrate metabolic and associated aerobic performance responses to ketogenic diets and ketone supplements.

Exogenous Ketone Supplementation and Ketogenic Diets for Exercise: Considering the Effect on Skeletal Muscle Metabolism

In recent years, ketogenic diets and ketone supplements have increased in popularity, particularly as a mechanism to improve exercise performance by modifying energetics. Since the skeletal muscle is a major metabolic and locomotory organ, it is important to take it into consideration when considering the effect of a dietary intervention, and the impact of physical activity on the body. The goal of this review is to summarize what is currently known and what still needs to be investigated concerning the relationship between ketone body metabolism and exercise, specifically in the skeletal muscle. Overall, it is clear that increased exposure to ketone bodies in combination with exercise can modify skeletal muscle metabolism, but whether this effect is beneficial or detrimental remains unclear and needs to be further interrogated before ketogenic diets or exogenous ketone supplementation can be recommended.

Age-related changes of skeletal muscle metabolic response to contraction are also sex-dependent

Mitochondria adapt to increased energy demands during muscle contraction by acutely altering metabolite fluxes and substrate oxidation. With age, an impaired mitochondrial metabolic response may contribute to reduced exercise tolerance and decreased skeletal muscle mass, specific force, increased overall fatty depositions in the skeletal muscle, frailty and depressed energy maintenance. We hypothesized that elevated energy stress in mitochondria with age alters the capacity of mitochondria to utilize different substrates following muscle contraction. To test this hypothesis, we used in vivo electrical stimulation to simulate high-intensity intervals (HII) or low intensity steady-state (LISS) exercise in young (5-7 months) and aged (27-29 months) male and female mice to characterize effects of age and sex on mitochondrial substrate utilization in skeletal muscle following contraction. Mitochondrial respiration using glutamate decreased in aged males following HII and glutamate oxidation was inhibited following HII in both the contracted and non-stimulated muscle of aged female muscle. Analyses of the muscle metabolome of female mice indicated that changes in metabolic pathways induced by HII and LISS contractions in young muscle are absent in aged muscle. To test improved mitochondrial function on substrate utilization following HII, we treated aged females with elamipretide (ELAM), a mitochondrially-targeted peptide shown to improve mitochondrial bioenergetics and restore redox status in aged muscle. ELAM removed inhibition of glutamate oxidation and showed increased metabolic pathway changes following HII, suggesting rescuing redox status and improving bioenergetic function in mitochondria from aged muscle increases glutamate utilization and enhances the metabolic response to muscle contraction in aged muscle. KEY POINTS: Acute local contraction of gastrocnemius can systemically alter mitochondrial respiration in non-stimulated muscle. Age-related changes in mitochondrial respiration using glutamate or palmitoyl carnitine following contraction are sex-dependent. Respiration using glutamate after high-intensity contraction is inhibited in aged female muscle. Metabolite level and pathway changes following muscle contraction decrease with age in female mice. Treatment with the mitochondrially-targeted peptide elamipretide can partially rescue metabolite response to muscle contraction.

Ketone body 3-hydroxybutyrate elevates cardiac output through peripheral vasorelaxation and enhanced cardiac contractility

The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output and myocardial perfusion without affecting blood pressure in humans, but the cardiovascular sites of action remain obscure. Here, we test the hypothesis in rats that 3-OHB acts directly on the heart to increase cardiac contractility and directly on blood vessels to lower systemic vascular resistance. We investigate effects of 3-OHB on (a) in vivo hemodynamics using echocardiography and invasive blood pressure measurements, (b) isolated perfused hearts in Langendorff systems, and (c) isolated arteries and veins in isometric myographs. We compare Na-3-OHB to equimolar NaCl added to physiological buffers or injection solutions. At plasma concentrations of 2-4 mM in vivo, 3-OHB increases cardiac output (by 28.3±7.8%), stroke volume (by 22.4±6.0%), left ventricular ejection fraction (by 13.3±4.6%), and arterial dP/dtmax (by 31.9±11.2%) and lowers systemic vascular resistance (by 30.6±11.2%) without substantially affecting heart rate or blood pressure. Applied to isolated perfused hearts at 3-10 mM, 3-OHB increases left ventricular developed pressure by up to 26.3±7.4 mmHg and coronary perfusion by up to 20.2±9.5%. Beginning at 1-3 mM, 3-OHB relaxes isolated coronary (EC50=12.4 mM), cerebral, femoral, mesenteric, and renal arteries as well as brachial, femoral, and mesenteric veins by up to 60% of pre-contraction within the pathophysiological concentration range. Of the two enantiomers that constitute racemic 3-OHB, D-3-OHB dominates endogenously; but tested separately, the enantiomers induce similar vasorelaxation. We conclude that increased cardiac contractility and generalized systemic vasorelaxation can explain the elevated cardiac output during 3-OHB administration. These actions strengthen the therapeutic rationale for 3-OHB in heart failure management.

Intracellular energy production and distribution in hypoxia

The hydrolysis of ATP is the primary source of metabolic energy for eukaryotic cells. Under physiological conditions, cells generally produce more than sufficient levels of ATP to fuel the active biological processes necessary to maintain homeostasis. However, mechanisms underpinning the distribution of ATP to subcellular microenvironments with high local demand remain poorly understood. Intracellular distribution of ATP in normal physiological conditions has been proposed to rely on passive diffusion across concentration gradients generated by ATP producing systems such as the mitochondria and the glycolytic pathway. However, subcellular microenvironments can develop with ATP deficiency due to increases in local ATP consumption. Alternatively, ATP production can be reduced during bioenergetic stress during hypoxia. Mammalian cells therefore need to have the capacity to alter their metabolism and energy distribution strategies to compensate for local ATP deficits while also controlling ATP production. It is highly likely that satisfying the bioenergetic requirements of the cell involves the regulated distribution of ATP producing systems to areas of high ATP demand within the cell. Recently, the distribution (both spatially and temporally) of ATP-producing systems has become an area of intense investigation. Here, we review what is known (and unknown) about intracellular energy production and distribution and explore potential mechanisms through which this targeted distribution can be altered in hypoxia, with the aim of stimulating investigation in this important, yet poorly understood field of research.

A Novel Powder Formulation of the Ketone Ester, Bis Hexanoyl (R)-1,3-Butanediol, Rapidly Increases Circulating ß-Hydroxybutyrate Concentrations in Healthy Adults

Objective: Growing interest in the metabolic state of ketosis has driven development of exogenous ketone products to induce ketosis without dietary changes. Bis hexanoyl (R)-1,3-butanediol (BH-BD) is a novel ketone ester which, when consumed, increases blood beta-hydroxybutyrate (BHB) concentrations. BH-BD is formulated as a powder or ready-to-drink (RTD) beverage; the relative efficacy of these formulations is unknown, but hypothesized to be equivalent.Methods: This randomized, observer-blinded, controlled, crossover decentralized study in healthy adults (n = 15, mean age = 33.7 years, mean BMI = 23.6 kg/m2) aimed to elucidate blood BHB and glucose concentrations before and 15, 30, 45, 60, 90 and 120 minutes following two serving sizes of reconstituted BH-BD powder (POW 25 g, POW 12.5 g), compared to a RTD BH-BD beverage (RTD 12.5 g), and a non-ketogenic control, all taken with a standard meal.Results: All BH-BD products were well tolerated and increased BHB, inducing nutritional ketosis (BHB ≥0.5 mM) after ∼15 minutes, relative to the control. BHB remained elevated 2 h post-consumption. The control did not increase BHB. Ketosis was dose responsive; peak BHB concentration and area under the curve (AUC) were two-fold greater with POW 25 g compared to POW 12.5 g and RTD 12.5 g. There were no differences in peak BHB and AUC between matched powder and RTD formulas. Blood glucose increased in all conditions following the meal but there were neither significant differences in lowest observed concentrations, nor consistent differences at each time point between conditions. These results demonstrate that both powdered and RTD BH-BD formulations similarly induce ketosis with no differences in glucose concentrations in healthy adults.

Comparative Metabolomics in Single Ventricle Patients after Fontan Palliation: A Strong Case for a Targeted Metabolic Therapy

Most studies on single ventricle (SV) circulation take a physiological or anatomical approach. Although there is a tight coupling between cardiac contractility and metabolism, the metabolic perspective on this patient population is very recent. Early findings point to major metabolic disturbances, with both impaired glucose and fatty acid oxidation in the cardiomyocytes. Additionally, Fontan patients have systemic metabolic derangements such as abnormal glucose metabolism and hypocholesterolemia. Our literature review compares the metabolism of patients with a SV circulation after Fontan palliation with that of patients with a healthy biventricular (BV) heart, or different subtypes of a failing BV heart, by Pubmed review of the literature on cardiac metabolism, Fontan failure, heart failure (HF), ketosis, metabolism published in English from 1939 to 2023. Early evidence demonstrates that SV circulation is not only a hemodynamic burden requiring staged palliation, but also a metabolic issue with alterations similar to what is known for HF in a BV circulation. Alterations of fatty acid and glucose oxidation were found, resulting in metabolic instability and impaired energy production. As reported for patients with BV HF, stimulating ketone oxidation may be an effective treatment strategy for HF in these patients. Few but promising clinical trials have been conducted thus far to evaluate therapeutic ketosis with HF using a variety of instruments, including ketogenic diet, ketone esters, and sodium-glucose co-transporter-2 (SGLT2) inhibitors. An initial trial on a small cohort demonstrated favorable outcomes for Fontan patients treated with SGLT2 inhibitors. Therapeutic ketosis is worth considering in the treatment of Fontan patients, as ketones positively affect not only the myocardial energy metabolism, but also the global Fontan physiopathology. Induced ketosis seems promising as a concerted therapeutic strategy.

The Effects of Ketogenic Diet on Insulin Sensitivity and Weight Loss, Which Came First: The Chicken or the Egg?

The ketogenic diet (KD) is, nowadays, considered an interesting nutritional approach for weight loss and improvement in insulin resistance. Nevertheless, most of the studies available in the literature do not allow a clear distinction between its effects on insulin sensitivity per se, and the effects of weight loss induced by KDs on insulin sensitivity. In this review, we discuss the scientific evidence on the direct and weight loss mediated effects of KDs on glycemic status in humans, describing the KD's biochemical background and the underlying mechanisms.

Effect of Exogenous Acute β-Hydroxybutyrate Administration on Different Modalities of Exercise Performance in Healthy Rats

PURPOSE

A ketone body (β-hydroxybutyrate [β-HB]) is used as an energy source in the peripheral tissues. However, the effects of acute β-HB supplementation on different modalities of exercise performance remain unclear. This study aimed to assess the effects of acute β-HB administration on the exercise performance of rats.

METHODS

In study 1, Sprague-Dawley rats were randomly divided into six groups: endurance exercise (EE + PL and EE + KE), resistance exercise (RE + PL and RE + KE), and high-intensity intermittent exercise (HIIE + PL and HIIE + KE) with placebo (PL) or β-HB salt (KE) administration. In study 2, metabolome analysis using capillary electrophoresis mass spectrometry was performed to profile the effects of β-HB salt administration on HIIE-induced metabolic responses in the skeletal and heart muscles.

RESULTS

The maximal carrying capacity (rest for 3 min after each ladder climb, while carrying heavy weights until the rats could not climb) in the RE + KE group was higher than that in the RE + PL group. The maximum number of HIIE sessions (a 20-s swimming session with a 10-s rest between sessions, while bearing a weight equivalent to 16% of body weight) in the HIIE + KE group was higher than that in the HIIE + PL group. However, there was no significant difference in the time to exhaustion at 30 m·min -1 between the EE + PL and the EE + KE groups. Metabolome analysis showed that the overall tricarboxylic acid cycle and creatine phosphate levels in the skeletal muscle were higher in the HIIE + KE group than those in the HIIE + PL group.

CONCLUSIONS

These results indicate that acute β-HB salt administration may accelerate HIIE and RE performance, and the changes in metabolic responses in the skeletal muscle after β-HB salt administration may be involved in the enhancement of HIIE performance.

The Computational Acid-Base Chemistry of Hepatic Ketoacidosis

Opposing evidence exists for the source of the hydrogen ions (H⁺) during ketoacidosis. Organic and computational chemistry using dissociation constants and alpha equations for all pertinent ionizable metabolites were used to (1) document the atomic changes in the chemical reactions of ketogenesis and ketolysis and (2) identify the sources and quantify added fractional (~) H⁺ exchange (~H⁺e). All computations were performed for pH conditions spanning from 6.0 to 7.6. Summation of the ~H⁺e for given pH conditions for all substrates and products of each reaction of ketogenesis and ketolysis resulted in net reaction and pathway ~H⁺e coefficients, where negative revealed ~H⁺ release and positive revealed ~H⁺ uptake. Results revealed that for the liver (pH = 7.0), the net ~H⁺e for the reactions of ketogenesis ending in each of acetoacetate (AcAc), β-hydroxybutyrate (β-HB), and acetone were -0.9990, 0.0026, and 0.0000, respectively. During ketogenesis, ~H⁺ release was only evident for HMG CoA production, which is caused by hydrolysis and not ~H⁺ dissociation. Nevertheless, there is a net ~H⁺ release during ketogenesis, though this diminishes with greater proportionality of acetone production. For reactions of ketolysis in muscle (pH = 7.1) and brain (pH = 7.2), net ~H⁺ coefficients for β-HB and AcAc oxidation were -0.9649 and 0.0363 (muscle), and -0.9719 and 0.0291 (brain), respectively. The larger ~H⁺ release values for β-HB oxidation result from covalent ~H⁺ release during the oxidation-reduction. For combined ketogenesis and ketolysis, which would be the metabolic condition in vivo, the net ~H⁺ coefficient depends once again on the proportionality of the final ketone body product. For ketone body production in the liver, transference to blood, and oxidation in the brain and muscle for a ratio of 0.6:0.2:0.2 for β-HB:AcAc:acetone, the net ~H⁺e coefficients for liver ketogenesis, blood transfer, brain ketolysis, and net total (ketosis) equate to -0.1983, -0.0003, -0.2872, and -0.4858, respectively. The traditional theory of ketone bodies being metabolic acids causing systemic acidosis is incorrect. Summation of ketogenesis and ketolysis yield H⁺ coefficients that differ depending on the proportionality of ketone body production, though, in general, there is a small net H⁺ release during ketosis. Products formed during ketogenesis (HMG-CoA, acetoacetate, β-hydroxybutyrate) are created as negatively charged bases, not acids, and the final ketone body, acetone, does not have pH-dependent ionizable groups. Proton release or uptake during ketogenesis and ketolysis are predominantly caused by covalent modification, not acid dissociation/association. Ketosis (ketogenesis and ketolysis) results in a net fractional H⁺ release. The extent of this release is dependent on the final proportionality between acetoacetate, β-hydroxybutyrate, and acetone.

A systematic review and meta-regression of exogenous ketone infusion rates and resulting ketosis-A tool for clinicians and researchers

Introduction: Ketone bodies such as beta-hydroxybutyrate (BHB) have pleiotropic functional benefits as fuel and signaling metabolites and may have multiple clinical applications. An alternative to inducing ketosis by dietary modification is intravenous delivery of exogenous sources of ketones. It is unknown whether there is a strong relationship between BHB infusion rate and blood BHB concentrations in the published literature; this information is vital for clinical studies investigating therapeutic effects of ketosis. This systematic review aimed to aggregate available data and address this gap. Methods: The PubMed and EMBASE databases were searched, and data were extracted from 23 manuscripts where BHB was infused and maximum and/or steady state BHB levels assessed. Infusion rate was adjusted when racemic BHB was infused but only D-BHB was measured. Results: Using a random effects meta-regression, strong linear relationships between BHB infusion rate and maximal (y = 0.060 + 0.870x, R 2 = 87.2%, p < 0.0001) and steady state (y = -0.022 + 0.849x, R 2 = 86.9%, p < 0.0001) blood BHB concentrations were found. Sensitivity analysis found this relationship was stronger when studies in non-healthy populations were excluded (y = 0.059 + 0.831x, R 2 = 96.3%, p < 0.0001). Conclusion: There is a strong relationship between BHB infusion rate and blood BHB concentrations; the regressions described here can be used by clinicians or researchers to determine ketone delivery required for a target blood concentration.

Scraping Therapy Improved Muscle Regeneration through Regulating GLUT4/Glycolytic and AMPK/mTOR/4EBP1 Pathways in Rats with Lumbar Multifidus Injury

Background

High morbidity of nonspecific low back pain (NLBP) and large consumption of medical resources caused by it have become a heavy social burden. There are many factors inducing NLBP, among which the damage and atrophy of multifidus (MF) are most closely related to NLBP. Scraping therapy can have significant treatment effects on NLBP with fewer adverse reactions and less medical fund input than other modalities or medications. However, the mechanism of scraping therapy treating NLBP remains unclarified. Here, we wanted to investigate the effects of scraping therapy on promoting MF regeneration and the underlying mechanisms.

Methods

A total of 54 male rats (SD, 6-7 weeks old) were randomly divided into nine groups, namely, K, M6h, M1d, M2d, M3d, G6h, G1d, G2d, and G3d, with six rats in each group. They were injected with bupivacaine (BPVC) to intentionally induce MF injury. We then performed scraping therapy on the rats that had been randomly chosen and compared treatment effects at different time points. In vitro data including skin temperature and tactile allodynia threshold were collected and histological sections were analyzed. mRNA sequencing was applied to distinguish the genes or signaling pathways that had been altered due to scraping therapy, and the results were further verified through reverse transcription polymerase chain reaction and Western blot analysis.

Results

Transitory petechiae and ecchymosis both on and beneath the rats' skin raised by scraping therapy gradually faded in about 3 d. Cross-sectional area (CSA) of MF was significantly smaller 30 h, 2 d, and 4 d after modeling (P=0.007, P=0.001, and P=0.015, respectively, vs. the blank group) and was significantly larger in the scraping group 1 d after treatment (P=0.002 vs. the model 1d group). Skin temperature significantly increased immediately after scraping (P < 0.001) and hindlimb pain threshold increased on the 2nd day after scraping (P=0.046 and P=0.028, respectively). 391 differentially expressed genes and 8 signaling pathways were characterized 6 h after scraping; only 3 differentially expressed genes and 3 signaling pathways were screened out 2 d after treatment. The amounts of mRNAs or proteins for GLUT4, HK2, PFKM, PKM, LDHA (which belong to the GLUT4/glycolytic pathway), p-mTOR, p-4EBP1 (which belong to the AMPK/mTOR/4EBP1 pathway), and BDH1 were enhanced, and p-AMPKα was decreased after scraping therapy.

Conclusions

Scraping therapy has therapeutic effects on rats with multifidus injury by promoting muscle regeneration via regulating GLUT4/glycolytic and AMPK/mTOR/4EBP1 signaling pathways.

Glycolytically impaired Drosophila glial cells fuel neural metabolism via β-oxidation

Neuronal function is highly energy demanding and thus requires efficient and constant metabolite delivery by glia. Drosophila glia are highly glycolytic and provide lactate to fuel neuronal metabolism. Flies are able to survive for several weeks in the absence of glial glycolysis. Here, we study how Drosophila glial cells maintain sufficient nutrient supply to neurons under conditions of impaired glycolysis. We show that glycolytically impaired glia rely on mitochondrial fatty acid breakdown and ketone body production to nourish neurons, suggesting that ketone bodies serve as an alternate neuronal fuel to prevent neurodegeneration. We show that in times of long-term starvation, glial degradation of absorbed fatty acids is essential to ensure survival of the fly. Further, we show that Drosophila glial cells act as a metabolic sensor and can induce mobilization of peripheral lipid stores to preserve brain metabolic homeostasis. Our study gives evidence of the importance of glial fatty acid degradation for brain function, and survival, under adverse conditions in Drosophila.

Ketones and the cardiovascular system

Ketone bodies, the main one being β-hydroxybutyrate, have emerged as important regulators of the cardiovascular system. In healthy individuals, as well as in individuals with heart failure or post-myocardial infarction, ketones provide a supplemental energy source for both the heart and the vasculature. In the failing heart, this additional energy may contribute to improved cardiac performance, whereas increasing ketone oxidation in vascular smooth muscle and endothelial cells enhances cell proliferation and prevents blood vessel rarefication. Ketones also have important actions in signaling pathways, posttranslational modification pathways and gene transcription; many of which modify cell proliferation, inflammation, oxidative stress, endothelial function and cardiac remodeling. Attempts to therapeutically increase ketone delivery to the cardiovascular system are numerous and have shown mixed results in terms of effectiveness. Here we review the bioenergetic and signaling effects of ketones on the cardiovascular system, and we discuss how ketones can potentially be used to treat cardiovascular diseases.

Metabolites as signalling molecules

Traditional views of cellular metabolism imply that it is passively adapted to meet the demands of the cell. It is becoming increasingly clear, however, that metabolites do more than simply supply the substrates for biological processes; they also provide critical signals, either through effects on metabolic pathways or via modulation of other regulatory proteins. Recent investigation has also uncovered novel roles for several metabolites that expand their signalling influence to processes outside metabolism, including nutrient sensing and storage, embryonic development, cell survival and differentiation, and immune activation and cytokine secretion. Together, these studies suggest that, in contrast to the prevailing notion, the biochemistry of a cell is frequently governed by its underlying metabolism rather than vice versa. This important shift in perspective places common metabolites as key regulators of cell phenotype and behaviour. Yet the signalling metabolites, and the cognate targets and transducers through which they signal, are only beginning to be uncovered. In this Review, we discuss the emerging links between metabolism and cellular behaviour. We hope this will inspire further dissection of the mechanisms through which metabolic pathways and intermediates modulate cell function and will suggest possible drug targets for diseases linked to metabolic deregulation.

High-Fat-Diet Suppressed Ketone Body Utilization for Lipogenic Pathway in Brown Adipose Tissues

Brown adipose tissue (BAT) consumes excess lipids and produces lipid metabolites as ketone bodies. These ketone bodies are then recycled for lipogenesis by the enzyme acetoacetyl-CoA synthetase (AACS). Previously, we found that a high-fat diet (HFD) upregulated AACS expression in white adipose tissue. In this study, we investigated the effects of diet-induced obesity on AACS in BAT. When 4-week-old ddY mice were fed a HFD or high-sucrose diet (HSD) for 12 weeks, a significant decrease in Aacs, acetyl-CoA carboxylase-1 (Acc-1), and fatty acid synthase (Fas) expression was observed in the BAT of the HFD group, whereas expression was not affected in the HSD group. In vitro analysis showed decreased Aacs and Fas expression in rat primary-cultured brown adipocytes following isoproterenol treatment for 24 h. In addition, the suppression of Aacs by siRNA markedly decreased the expression of Fas and Acc-1 but did not affect the expression of uncoupling protein-1 (UCP-1) or other factors. These results suggested that HFD may suppress ketone body utilization for lipogenesis in BAT and that AACS gene expression may be important for regulating lipogenesis in BAT. Therefore, the AACS-mediated ketone body utilization pathway may regulate lipogenesis under conditions of excess dietary fat.

On the interdependence of ketone body oxidation, glycogen content, glycolysis and energy metabolism in the heart

In heart, glucose and glycolysis are important for anaplerosis and potentially therefore for d-β-hydroxybutyrate (βHB) oxidation. As a glucose store, glycogen may also furnish anaplerosis. We determined the effects of glycogen content on βHB oxidation and glycolytic rates, and their downstream effects on energetics, in the isolated rat heart. High glycogen (HG) and low glycogen (LG) containing hearts were perfused with 11 mM [5-3 H]glucose and/or 4 mM [14 C]βHB to measure glycolytic rates or βHB oxidation, respectively, then freeze-clamped for glycogen and metabolomic analyses. Free cytosolic [NAD+ ]/[NADH] and mitochondrial [Q+ ]/[QH2 ] ratios were estimated using the lactate dehydrogenase and succinate dehydrogenase reaction, respectively. Phosphocreatine (PCr) and inorganic phosphate (Pi ) concentrations were measured using 31 P-nuclear magnetic resonance spectroscopy. Rates of βHB oxidation in LG hearts were half that in HG hearts, with βHB oxidation directly proportional to glycogen content. βHB oxidation decreased glycolysis in all hearts. Glycogenolysis in glycogen-replete hearts perfused with βHB alone was twice that of hearts perfused with βHB and glucose, which had significantly higher levels of the glycolytic intermediates fructose 1,6-bisphosphate and 3-phosphoglycerate, and higher free cytosolic [NAD+ ]/[NADH]. βHB oxidation increased the Krebs cycle intermediates citrate, 2-oxoglutarate and succinate, the total NADP/H pool, reduced mitochondrial [Q+ ]/[QH2 ], and increased the calculated free energy of ATP hydrolysis (∆GATP ). Although βHB oxidation inhibited glycolysis, glycolytic intermediates were not depleted, and cytosolic free NAD remained oxidised. βHB oxidation alone increased Krebs cycle intermediates, reduced mitochondrial Q and increased ∆GATP . We conclude that glycogen facilitates cardiac βHB oxidation by anaplerosis. KEY POINTS: Ketone bodies (d-β-hydroxybutyrate, acetoacetate) are increasingly recognised as important cardiac energetic substrates, in both healthy and diseased hearts. As 2-carbon equivalents they are cataplerotic, causing depletion of Krebs cycle intermediates; therefore their utilisation requires anaplerotic supplementation, and intra-myocardial glycogen has been suggested as a potential anaplerotic source during ketone oxidation. It is demonstrated here that cardiac glycogen does indeed provide anaplerotic substrate to facilitate β-hydroxybutyrate oxidation in isolated perfused rat heart, and this contribution was quantified using a novel pulse-chase metabolic approach. Further, using metabolomics and 31 P-MR, it was shown that glycolytic flux from myocardial glycogen increased the heart's ability to oxidise βHB, and βHB oxidation increased the mitochondrial redox potential, ultimately increasing the free energy of ATP hydrolysis.

Ketone Monoester Plus Carbohydrate Supplementation Does Not Alter Exogenous and Plasma Glucose Oxidation or Metabolic Clearance Rate During Exercise in Men Compared with Carbohydrate Alone

BACKGROUND

Increasing β-hydroxybutyrate (βHB) availability through ketone monoester plus carbohydrate (KE+CHO) supplementation is suggested to enhance physical performance by sparing glucose use during exercise. However, no studies have examined the effect of ketone supplementation on glucose kinetics during exercise.

OBJECTIVES

This exploratory study primarily aimed to determine the effect of KE+CHO supplementation on glucose oxidation and physical performance during steady-state exercise compared with carbohydrate.

METHODS

Using a randomly assigned, crossover design (clinicaltrials.gov, NCT04737694), 12 men consumed KE+CHO (573 mg ketone monoester/kg body mass, 110 g glucose) or carbohydrate (110 g glucose) before and during 90 min of steady-state treadmill exercise [54 ± 3% peak oxygen uptake (V̇˙O_2peak)] wearing a weighted vest (30% body mass; 25 ± 3 kg). Glucose oxidation and turnover were determined using indirect calorimetry and stable isotopes. Participants performed an unweighted time to exhaustion (TTE; 85% V̇˙O_2peak) after steady-state exercise and a weighted (25 ± 3 kg) 6.4 km time trial (TT) the next day after consuming a bolus of KE+CHO or carbohydrate. Data were analyzed by paired t-tests and mixed model ANOVA.

RESULTS

βHB concentrations were higher (P < 0.05) after exercise [2.1 mM (95% CI: 1.6, .6)] and the TT [2.6 mM (2.1, 3.1)] in KE+CHO compared with carbohydrate. TTE was lower [-104 s (-201, -8)], and TT performance was slower [141 s (19,262)] in KE+CHO than in carbohydrate (P < 0.05). Exogenous [-0.01 g/min (-0.07, 0.04)] and plasma [-0.02 g/min (-0.08, 0.04)] glucose oxidation and metabolic clearance rate {MCR [0.38 mg·kg^-1·min^-1 (-0.79, 1.54)]} were not different, and glucose rate of appearance [-0.51 mg·kg^-1·min^-1 (-0.97, -0.04)], and disappearance [-0.50 mg·kg^-1·min^-1 (-0.96, -0.04)] were lower (P < 0.05) in KE+CHO compared with carbohydrate during steady-state exercise.

CONCLUSIONS

In the current study, the rates of exogenous and plasma glucose oxidation and MCR were not different between treatments during steady-state exercise, suggesting blood glucose utilization is similar between KE+CHO and carbohydrate. KE+CHO supplementation also results in lower physical performance compared with carbohydrate. This trial was registered at www.

CLINICALTRIALS

gov as NCT04737694.

Ketone Bodies and Cardiovascular Disease: An Alternate Fuel Source to the Rescue

The increased metabolic activity of the heart as a pump involves a high demand of mitochondrial adenosine triphosphate (ATP) production for its mechanical and electrical activities accomplished mainly via oxidative phosphorylation, supplying up to 95% of the necessary ATP production, with the rest attained by substrate-level phosphorylation in glycolysis. In the normal human heart, fatty acids provide the principal fuel (40-70%) for ATP generation, followed mainly by glucose (20-30%), and to a lesser degree (<5%) by other substrates (lactate, ketones, pyruvate and amino acids). Although ketones contribute 4-15% under normal situations, the rate of glucose use is drastically diminished in the hypertrophied and failing heart which switches to ketone bodies as an alternate fuel which are oxidized in lieu of glucose, and if adequately abundant, they reduce myocardial fat delivery and usage. Increasing cardiac ketone body oxidation appears beneficial in the context of heart failure (HF) and other pathological cardiovascular (CV) conditions. Also, an enhanced expression of genes crucial for ketone break down facilitates fat or ketone usage which averts or slows down HF, potentially by avoiding the use of glucose-derived carbon needed for anabolic processes. These issues of ketone body utilization in HF and other CV diseases are herein reviewed and pictorially illustrated.

Short- and long-term cognitive and metabolic effects of medium-chain triglyceride supplementation in rats

Medium-chain triglycerides (MCT) possess neuroprotective properties. However, the long-term metabolic consequences of supplementing a regular diet with cognition-enhancing doses of MCT are largely unknown. We studied the effects of chronic (28 days) supplementation of regular diet with different doses of MCT oil (1, 3, or 6 g/kg/day) or water (control) on working memory (Y-maze), behavior in the Open Field, spatial learning (Morris water maze), and weight of internal organs in male Wistar 2.5-m.o. Rats. In a separate experiment, we evaluated acute (single gavage) and chronic (28 days) effects of MCT or lard supplementation (3 g/kg) on blood biochemical parameters. MCT-1 and MCT-3 doses improved working memory in YM. In MWM, MCT-6 treatment improved spatial memory. Chronic MCT-1 or MCT-3 treatment did not affect internal organ weight, while MCT-6 dose increased liver weight and the brown/white adipose tissue ratio. Acutely, MCT administration elevated blood β-hydroxybutyrate and malondialdehyde levels. Chronic MCT administration (3 g/kg) did not affect the blood levels of glucose, lactate, pyruvate, acetoacetate, β-hydroxybutyrate, total and HDL cholesterol, triglycerides, malondialdehyde, and aspartate transaminase and alanine transaminase activities. Therefore, daily supplementation of standard feed with MCT resulted in mild intermittent ketosis. It improved working memory at lower concentrations without significant adverse side effects. At higher concentrations, it improved long-term spatial memory but also resulted in organ weight changes and is likely unsafe. These results highlight the importance of monitoring the metabolic effects of MCT supplementation alongside cognitive assessment in future studies of MCT's neuroprotective properties.

Exogenous ketone supplementation: an emerging tool for physiologists with potential as a metabolic therapy

NEW FINDINGS

What is the topic of this review? The integrative physiological response to exogenous ketone supplementation. What advances does it highlight? The physiological effects and therapeutic potential of exogenous ketones on metabolic health, cardiovascular function, cognitive processing, and modulation of inflammatory pathways and immune function. Also highlighted are current challenges and future directions of the field.

ABSTRACT

Exogenous oral ketone supplements, primarily in form of ketone salts or esters, have emerged as a useful research tool for manipulating metabolism with potential therapeutic application targeting various aspects of several common chronic diseases. Recent literature has investigated the effects of exogenously induced ketosis on metabolic health, cardiovascular function, cognitive processing, and modulation of inflammatory pathways and immune function. This narrative review provides an overview of the integrative physiological effects of exogenous ketone supplementation and highlights current challenges and future research directions. Much of the existing research on therapeutic applications - particularly mechanistic studies - has involved pre-clinical rodent and/or cellular models, requiring further validation in human clinical studies. Existing human studies report that exogenous ketones can lower blood glucose and improve some aspects of cognitive function, highlighting the potential therapeutic application of exogenous ketones for type 2 diabetes and neurological diseases. There is also support for the ability of exogenous ketosis to improve cardiac metabolism in rodent models of heart failure with supporting human studies emerging; long-terms effects of exogenous ketone supplementation on the human cardiovascular system and lipid profiles are needed. An important avenue for future work is provided by research accelerating technologies that enable continuous ketone monitoring and/or the development of more palatable ketone mixtures that optimize plasma ketone kinetics to enable sustained ketosis. Lastly, research exploring the physiological interactions between exogenous ketones and varying metabolic states (e.g., exercise, fasting, metabolic disease) should yield important insights that can be used to maximize the health benefits of exogenous ketosis.

Bis Hexanoyl (R)-1,3-Butanediol, a Novel Ketogenic Ester, Acutely Increases Circulating r- and s-ß-Hydroxybutyrate Concentrations in Healthy Adults

BACKGROUND

Ketosis has been reported to benefit healthspan and resilience, which has driven considerable interest in development of exogenous ketones to induce ketosis without dietary changes. Bis hexanoyl (R)-1,3-butanediol (BH-BD) is a novel ketone di-ester that can be used as a food ingredient that increases hepatic ketogenesis and blood beta-hydroxybutyrate (BHB) concentrations.

METHODS

Here, we provide the first description of blood ketone and metabolite kinetics for up to five hours after consumption of a beverage containing BH-BD by healthy adults (n = 8) at rest in three randomized, cross-over conditions (25 g + Meal (FEDH); 12.5 g + Meal (FEDL) ; 25 g + Fasted (FASTH)).

RESULTS

Consumption of BH-BD effectively raised plasma r-BHB concentrations to 0.8-1.7 mM in all conditions, and both peak r-BHB concentration and r-BHB area under the curve were greater with 25 g versus 12.5 g of BH-BD. Urinary excretion of r-BHB was <1 g. Plasma concentration of the non-physiological isoform s-BHB was increased to 20-60 µM in all conditions. BH-BD consumption decreased plasma glucose and free fatty acid concentrations; insulin was increased when BH-BD was consumed with a meal.

CONCLUSIONS

These results demonstrate that consumption of BH-BD effectively induces exogenous ketosis in healthy adults at rest.

Still Excited, but Less Aroused-The Effects of Nutritional Ketosis on Epinephrine Response and Hypothalamic Orexin Neuron Activation Following Recurrent Hypoglycemia in Diabetic Rats

Hypoglycemia-associated autonomic failure (HAAF) is a serious, life-threatening complication of intensive insulin therapy, particularly in people with type 1 diabetes. The ketogenic diet is reported to beneficially affect glycemic control in people with type 1 diabetes, however its effects on the neurohormonal counterregulatory response to recurrent hypoglycemia and HAAF development are understudied. In this study we used Sprague Dawley rats to establish a HAAF model under non-diabetic and streptozotocin (STZ)-induced diabetic conditions and determined how nutritional ketosis affected the neurohormonal counterregulation and the activity of energy-sensing orexin (OX) neurons. We found that antecedent hypoglycemia diminished the sympathoexcitatory epinephrine response to subsequent hypoglycemia in chow-fed non-diabetic rats, but this did not occur in STZ-diabetic animals. In all cases a ketogenic diet preserved the epinephrine response. Contrary to expectations, STZ-diabetic keto-fed rats showed reduced OX activity in the recurrent hypoglycemia group, which did not occur in any other group. It is possible that the reduced activation of OX neurons is an adaptation aimed at energy conservation accompanied by diminished arousal and exploratory behaviour. Our data suggests that while a ketogenic diet has beneficial effects on glycemia, and epinephrine response, the reduced activation of OX neurons could be detrimental and warrants further investigation.

Ketogenic diets and Ketone suplementation: A strategy for therapeutic intervention

Ketogenic diets and orally administered exogenous ketone supplements are strategies to increase serum ketone bodies serving as an alternative energy fuel for high energy demanding tissues, such as the brain, muscles, and the heart. The ketogenic diet is a low-carbohydrate and fat-rich diet, whereas ketone supplements are usually supplied as esters or salts. Nutritional ketosis, defined as serum ketone concentrations of ≥ 0.5 mmol/L, has a fasting-like effect and results in all sorts of metabolic shifts and thereby enhancing the health status. In this review, we thus discuss the different interventions to reach nutritional ketosis, and summarize the effects on heart diseases, epilepsy, mitochondrial diseases, and neurodegenerative disorders. Interest in the proposed therapeutic benefits of nutritional ketosis has been growing the past recent years. The implication of this nutritional intervention is becoming more evident and has shown interesting potential. Mechanistic insights explaining the overall health effects of the ketogenic state, will lead to precision nutrition for the latter diseases.