Exogenous d ‐β‐hydroxybutyrate lowers blood glucose in part by decreasing the availability of L‐alanine for gluconeogenesis

Impact of endophyte-infected tall fescue seed consumption on endocrine changes associated with intake regulation and post-absorptive metabolism in growing steers

Fescue toxicosis is a syndrome occurring from the consumption of endophyte-infected tall fescue and results in substantial economic losses to the beef industry primarily from reduced growth accompanied by decreased dry matter intake (DMI); however, the associations characterizing this reduction in DMI have yet to be elucidated. The objective of this experiment was to identify endocrine changes associated with intake regulation post-consumption of endophyte-infected tall fescue seed (E+). Twelve Holstein steers were stratified by body weight and assigned to 1 of 3 treatments (n=4): 0 ppm ergovaline (ERV), 1.8 ppm ERV, or 2.7 ppm ERV. Treatments were achieved by combining differing proportions of ground E+ and non-endophyte-infected tall fescue seed. Steers were adapted to their diets for 7 d followed by a 7 d DMI collection period. Within treatment, steers were assigned to a sampling day (d 16 or d 17). Blood samples were collected every 20 min for 8 h, beginning 1 h before feeding. Intake data was analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC) with treatment, day, and the interaction as fixed effects. Hormone and metabolite data were analyzed with the fixed effect of treatment, time, and the interaction including time as a repeated measure and orthogonal contrasts. Dry matter intake was linearly decreased with increasing ERV in the diet (P < 0.001). Insulin and leptin concentrations exhibited a quadratic effect (P = 0.018 and P = 0.005) with insulin concentrations highest for the 2.7 ppm treatment and leptin concentrations highest for the 1.8 ppm treatment. No differences were detected for active ghrelin or β-hydroxybuytrate concentrations among treatment groups. Further, steers consuming both the 1.8 and 2.7 ppm ERV treatments had lower prolactin concentrations compared to the 0 ppm treatment (quadratic, P= 0.019). Glucose concentrations had a tendency for a linear increase as ERV concentrations increased (P = 0.091). A treatment × time interaction (P = 0.002) was noted in NEFA concentrations, with the 1.8 ppm ERV treatment showing increased pre-feeding concentrations, and the 2.7 ppm ERV treatment exhibiting elevated NEFA concentrations as time post-feeding progressed. The results suggest that E+ consumption reduces intake likely through alterations in intake-related hormones and post-absorptive metabolism and contributes to our current understanding of E+ effects on intake reduction while providing avenues for future research.

Exogenous ketone esters as a potential therapeutic for treatment of sarcopenic obesity

Identifying effective treatment(s) for sarcopenia and sarcopenic obesity is of paramount importance as the global population advances in age and obesity continues to be a worldwide concern. Evidence has shown that a ketogenic diet can be beneficial for the preservation of muscle quality and function in older adults, but long-term adherence is low due in part to the high-fat (≥80%), very low carbohydrate (<5%) composition of the diet. When provided in adequate amounts, exogenous ketone esters (KEs) can increase circulating ketones to concentrations that exceed those observed during prolonged fasting or starvation without significant alterations in the diet. Ketone esters first emerged in the mid-1990s and their use in preclinical and clinical research has escalated within the past 10-15 years. We present findings from a narrative review of the existing literature for a proposed hypothesis on the effects of exogenous ketones as a therapeutic for preservation of skeletal muscle and function within the context of sarcopenic obesity and future directions for exploration. Much of the reviewed literature herein examines the mechanisms of the ketone diester (R,S-1,3-butanediol diacetoacetate) on skeletal muscle mass, muscle protein synthesis, and epigenetic regulation in murine models. Additional studies are needed to further examine the key regulatory factors producing these effects in skeletal muscle, examine convergent and divergent effects among different ketone ester formulations, and establish optimal frequency and dosing regimens to translate these findings into humans.

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.

The effect of acute and 14-day exogenous ketone supplementation on glycemic control in adults with type 2 diabetes: two randomized controlled trials

Acute ingestion of the exogenous ketone monoester supplement [(R)-3-hydroxybutyl-(R)-3-hydroxybutyrate] lowers blood glucose, suggesting therapeutic potential in individuals with impaired glucose metabolism. However, it is unknown how acute or repeated ingestion of exogenous ketones affects blood glucose control in individuals with type 2 diabetes (T2D). We conducted two randomized, counterbalanced, double-blind, placebo-controlled crossover trials to determine if 1) acute exogenous ketone monoester (0.3 g/kg body mass; N = 18) or 2) 14-day thrice daily premeal exogenous ketone monoester (15 g; N = 15) supplementation could lower blood glucose in individuals living with T2D. A single dose of the ketone monoester supplement elevated blood β-OHB to ∼2 mM. There were no differences in the primary outcomes of plasma glucose concentration (acutely) or serum fructosamine (glycemic control across 14 days) between conditions. Ketone monoester ingestion acutely increased insulin and lowered nonesterified fatty acid concentrations; plasma metabolomics confirmed a reduction in multiple free fatty acids species and select gluconeogenic amino acids. In contrast, no changes were observed in fasting metabolic outcomes following 14 days of supplementation. In the context of these randomized controlled trials, acute or repeated ketone monoester ingestion in adults with T2D did not lower blood glucose when consumed acutely in a fasted state and did not improve glycemic control following thrice daily premeal ingestion across 14 days. Future studies exploring the mechanistic basis for the (lack of) glucose-lowering effect of exogenous ketone supplementation in T2D and other populations are warranted.NEW & NOTEWORTHY Exogenous ketone supplements can acutely lower blood glucose, suggesting therapeutic potential in individuals with impaired glucose metabolism. However, the effect of exogenous ketones on glucose metabolism in adults with type 2 diabetes has not been investigated in a controlled setting. In adults with type 2 diabetes, ketone monoester ingestion did not lower blood glucose acutely in a fasted state and did not improve glycemic control across thrice daily premeal ingestion across 14 days.

Tolerability and Acceptability of an Exogenous Ketone Monoester and Ketone Monoester/Salt Formulation in Humans

Exogenous ketone ester and ketone ester mixed with ketone free acid formulations are rapidly entering the commercial marketspace. Short-term animal and human studies using these products suggest significant potential for primary or secondary prevention of a number of chronic disease conditions. However, a number of questions need to be addressed by the field for optimal use in humans, including variable responses among available exogenous ketones at different dosages; frequency of dosing; and their tolerability, acceptability, and efficacy in long-term clinical trials. The purpose of the current investigation was to examine the tolerability, acceptability, and circulating R-beta-hydroxybutyrate (R-βHB) and glucose responses to a ketone monoester (KME) and ketone monoester/salt (KMES) combination at 5 g and 10 g total R-βHB compared with placebo control (PC). Fourteen healthy young adults (age: 21 ± 2 years, weight: 69.7 ± 14.2 kg, percent fat: 28.1 ± 9.3%) completed each of the five study conditions: placebo control (PC), 5 g KME (KME5), 10 g KME (KME10), 5 g (KMES5), and 10 g KMES (KMES10) in a randomized crossover fashion. Circulating concentrations of R-βHB were measured at baseline (time 0) following an 8-12 h overnight fast and again at 15, 30, 60, and 120 min following drink ingestion. Participants also reported acceptability and tolerability during each condition. Concentrations of R-βHB rose to 2.4 ± 0.1 mM for KME10 after 15 min, whereas KMES10 similarly peaked (2.1 ± 0.1 mM) but at 30 min. KME5 and KMES5 achieved similar peak R-βHB concentrations (1.2 ± 0.7 vs. 1.1 ± 0.5 mM) at 15 min. Circulating R-βHB concentrations were similar to baseline for each condition by 120 min. Negative correlations were observed between R-βHB and glucose at the 30 min time point for each condition except KME10 and PC. Tolerability was similar among KME and KMES, although decreases in appetite were more frequently reported for KMES. Acceptability was slightly higher for KMES due to the more frequently reported aftertaste for KME. The results of this pilot investigation illustrate that the KME and KMES products used increase circulating R-βHB concentrations to a similar extent and time course in a dose-dependent fashion with slight differences in tolerability and acceptability. Future studies are needed to examine variable doses, frequency, and timing of exogenous ketone administration for individuals seeking to consume ketone products for health- or sport performance-related purposes.

The effectiveness of blood glucose and blood ketone measurement in identifying significant acidosis in diabetic ketoacidosis patients

BACKGROUND

Patients with diabetic ketoacidosis (DKA), a potentially fatal complication of type 1 diabetes, have hyperglycemia, ketonemia and metabolic acidosis. Blood glucose and blood ketone results are often used to triage patients with suspected DKA. This study aimed to establish how effective blood glucose and blood ketone (beta-hydroxybutyrate, BOHB) measurements are in identifying patients with significant acidosis and sought to validate existing diagnostic BOHB thresholds.

METHODS

Initial Emergency Department results on 161 presumptive DKA episodes in 95 patients (42 F, 53 M, age range 14-89 years) containing a complete dataset of D (glucose), K (BOHB) and A (Bicarbonate [HCO3] and pH) results.

RESULTS

Blood glucose correlated poorly with BOHB (r = 0.28 p = 0.0003), pH (r= -0.25, p = 0.002) and HCO3 (r= -0.17, p = 0.04). BOHB, though better, was still limited in predicting pH (r = -0.44, p < 0.0001) and HCO3 (r = -0.49, p < 0.0001). A HCO3 of 18mmol/L equated to a BOHB concentration of 4.3mmol/L, whilst a HCO3 of 15mmol/L equated to a BOHB of 4.7mmol/L. Of the 133 of 161 events with HCO3 < 18mmol/L, 22 were not hyperglycemic (> 13.9mmol/L, n = 8), ketonemic (≤ 3mmol/L, n = 9) or either (n = 5).

CONCLUSIONS

The commonly employed BOHB diagnostic cutoff of 3mmol/L could not be verified. Since acid-base status was poorly predicted by both glucose and BOHB, this highlights that, regardless of their results, pH and/or HCO3 should also be tested in any patient suspected of DKA.

Ketogenic effects of medium chain triglycerides containing formula and its correlation to breath acetone in healthy volunteers: a randomized, double-blinded, placebo-controlled, single dose-response study

The efficacy of low-carbohydrate, high-fat diets, such as ketogenic diets, for cancer patients is of research interest. We previously demonstrated the efficacy of the ketogenic diet in a case study in which medium-chain triglycerides (MCTs) or MCT-containing formula (ketogenic formula) was used as a supplement to increase blood ketone bodies. However, little is known about the amounts needed to induce ketogenic effects and about the usefulness of monitoring of breath acetone. To investigate the pharmacokinetics of MCTs and their metabolites, blood ketone bodies and breath acetone, 24 healthy subjects received one of four single oral doses of the ketogenic formula (equivalent to 0, 10, 20, and 30 g of MCTs) under fasting conditions. Total blood ketone bodies, β-hydroxybutyrate, octanoic acid, and decanoic acid were increased in a dose-dependent manner. The ketogenic effect was considered to depend on octanoic and decanoic acids, because a positive correlation was observed between them. A strong positive correlation was also observed between total serum ketone bodies and breath acetone at each time points. Therefore, monitoring breath acetone levels seems a less invasive method to predict blood concentrations of ketone bodies during ketogenic diet therapy. Clinical trial registration:https://rctportal.niph.go.jp/en/detail?trial_id=UMIN000032634, UMIN-CTR UMIN000032634.

Fasting Ketone Bodies and Incident Type 2 Diabetes in the General Population

With rising incidence and prevalence of type 2 diabetes, prevention including identification of prospective biomarkers becomes increasingly relevant. Although ketone bodies recently received a renewed interest as potential biomarkers, data linking these metabolites to diabetes risk are scarce. Therefore, the present prospective study investigated a potential association between fasting ketone bodies and incident type 2 diabetes in the general population. This study from the PREVEND cohort included 3,307 participants from the general population initially free of diabetes or impaired fasting glucose. Baseline fasting ketone body concentrations were measured by nuclear magnetic resonance spectroscopy. One hundred twenty-six participants (3.8%) developed type 2 diabetes during a median (interquartile range) follow-up of 7.3 (6.3-7.6) years. In Kaplan-Meier analysis, sex-stratified ketone body levels strongly positively associated with incident type 2 diabetes, which was confirmed in Cox regression analyses adjusted for several potential confounders. There was no significant interaction by sex. Both 3-β-hydroxybutyrate and acetoacetate+acetone individually associated with incident type 2 diabetes. In conclusion, fasting plasma ketone body levels are strongly positively associated with incident type 2 diabetes in the general population independent of several other recognized risk factors. These results may have important implications for diabetes prevention including dietary strategies.

ARTICLE HIGHLIGHTS

The identification of biomarkers that predict type 2 diabetes is increasingly relevant for personalized medicine strategies. Data regarding ketone bodies and incident type 2 diabetes are scarce. This study shows that ketone bodies, either combined or as individual subspecies, are strongly associated with incident type 2 diabetes in the general population, independent of potential confounders. These results may have important implications for diabetes prevention including dietary strategies.

Evaluation of the safety and tolerability of exogenous ketosis induced by orally administered free beta-hydroxybutyrate in healthy adult subjects

Beta-hydroxybutyrate (D-BHB) is a metabolite with intrinsic signalling activity that has gained attention as a potentially clinically useful supplement. There are available supplements for inducing ketosis: ketone salts, ketone esters and medium-chain triglycerides. Even when all of them raise D-BHB in the blood and all are safe and well tolerated, they significantly differ in their safety profile, their palatability and their price. A fourth and potentially interesting option is to use biologically identical D-BHB, which it is already commercially available in the USA (American Ketone) and Greater China (MedPHA). However, its safety and tolerability had not yet been documented in the scientific literature. We evaluated the safety and tolerability of orally administered free D-BHB in a gender and age-balanced sample of 24 asymptomatic and overtly healthy adults. No participant showed acid-base abnormalities or electrolyte abnormalities. Secondary symptoms were reported after only 6.2% of all drink takes and none of the reports described the symptom as 'severe'. The most frequently reported secondary effects (19/720 or 2.6%) were gastrointestinal discomfort, headache (7/720 or 1%) and loss of appetite (7/720 or 1%). No correlation between weight-adjusted dose and frequency of secondary symptoms was observed. Free D-BHB was a safe and well-tolerated intervention for inducing sustained exogenous ketosis. Being bioidentical, salt-free and lacking intermediate metabolites, this form of supplementation could have a larger safety spectrum than salt or alcohol-based exogenous ketones. More research is warranted to assess its clinical efficacy in those clinical scenarios in which achieving ketosis rapidly could be beneficial.

Effects of ketone supplements on blood β-hydroxybutyrate, glucose and insulin: A systematic review and three-level meta-analysis

BACKGROUND

Effects of ketone supplements as well as relevant dose-response relationships and time effects on blood β-hydroxybutyrate (BHB), glucose and insulin are controversial.

OBJECTIVE

This study aimed to summarize the existing evidence and synthesize the results, and demonstrate underlying dose-response relationships as well as sustained time effects.

METHODS

Medline, Web of Science, Embase, and Cochrane Central Register of Controlled Trials were searched for relevant randomized crossover/parallel studies published until 25th November 2022. Three-level meta-analysis compared the acute effects of exogenous ketone supplementation and placebo in regulating blood parameters, with Hedge's g used as measure of effect size. Effects of potential moderators were explored through multilevel regression models. Dose-response and time-effect models were established via fractional polynomial regression.

RESULTS

The meta-analysis with 327 data points from 30 studies (408 participants) indicated that exogenous ketones led to a significant increase in blood BHB (Hedge's g = 1.4994, 95% CI [1.2648, 1.7340]), reduction in glucose (Hedge's g = -0.3796, 95% CI [-0.4550, -0.3041]), and elevation in insulin of non-athlete healthy population (Hedge's g = 0.1214, 95%CI [0.0582, 0.3011]), as well as insignificant change in insulin of obesity and prediabetes. Nonlinear dose-response relationship between ketone dosage and blood parameter change was observed in some time intervals for BHB (30-60 min; >120 min) and insulin (30-60 min; 90-120 min), with linear relationship observed for glucose (>120 min). Nonlinear associations between time and blood parameter change were found in BHB (>550 mg/kg) and glucose (450-550 mg/kg), with linear relationship observed in BHB (≤250 mg/kg) and insulin (350-550 mg/kg).

CONCLUSION

Dose-response relationships and sustained time effects were observed in BHB, glucose and insulin following ketone supplementation. Glucose-lowering effect without increasing insulin load among population of obesity and prediabetes was of remarkable clinical implication.

REGISTRY AND REGISTRY NUMBER

PROSPERO (CRD42022360620).

Fasting and diurnal blood ketonemia and glycemia responses to a six-week, energy-controlled ketogenic diet, supplemented with racemic R/S-BHB salts

BACKGROUND

Single doses of exogenous ketone salts (KS) transiently increase circulating beta-hydroxybutyrate (BHB) (∼1 mM; 1-2 h) regardless of starting levels of ketosis; however, no studies have explored how sustained use of KS influences measures of ketonemia and glycemia.

OBJECTIVES

To determine the response to a hypocaloric, well-formulated ketogenic diet (KD), with and without the inclusion of two daily racemic KS doses (6 g R-BHB + 6 g S-BHB per serving) on 1) daily fasting capillary R-BHB and glucose (R-BHB/GLU_fast), 2) bi-weekly 13 h diurnal BHB and glucose (R-BHB/GLU_diur), 3) three-hours post-KS ingestion kinetics (R-BHB_KS), and 4) bi-weekly fasting plasma enantiomer-specific BHB (R/S-BHB_plasma).

METHODS

Non-diabetic adults with overweight and obesity were randomized to receive a precisely measured hypocaloric KD (∼75 %en of maintenance) for six weeks, supplemented twice-daily with KS or placebo (PL). A non-randomized comparison group was provided an isonitrogenous/isoenergetic low-fat diet (LFD). All meals were provided to subjects. Capillary blood was collected daily to measure R-BHB/GLU_fast and hourly for R-BHB/GLU_diur. Plasma was collected to measure R/S-BHB_plasma, insulin, fasting glucose, and insulin resistance (HOMA-IR). Total AUC was calculated using the trapezoidal method.

RESULTS

Mean R-BHB_fast increased significantly during KD + PL (1.0 mM BHB), an effect enhanced 26% during KD + KS. GLU_fast AUC was -6% lower during KD + KS versus LFD. Mean R-BHB_diur increased 40% in KD + KS versus KD + PL, whereas GLU_diur decreased 13% during both KDs versus LFD. R-BHB_KS peaked (Δ: ∼1 mM) 1 h after the morning KS dose, but not following the afternoon dose. Both R/S-BHB_plasma increased during KD independent of KS inclusion. R-BHB_plasma was 50-times greater compared to S-BHB_plasma, and the KS augmented S-BHB_plasma 50% more than PL. Fasting insulin and HOMA-IR decreased after 14 days independent of diet.

CONCLUSIONS

A hypocaloric KD was effective at reducing diurnal glucose compared to a LFD independent of weight loss, but twice-daily racemic KS ingestion during KD augmented ketonemia, both as R- and S-BHB, and decreased mean fasting glucose beyond a KD alone. The hypoglycemic effects of KD in combination with exogenous ketones merit further investigation.

The Effect of Novel Exogenous Ketone Supplements on Blood Beta-Hydroxybutyrate and Glucose

Exogenous ketone monoesters can raise blood β-OHB and lower glucose without other nutritional modifications or invasive procedures. However, unpleasant taste and potential gastrointestinal discomfort may make adherence to supplementation challenging. Two novel ketone supplements promise an improved consumer experience but differ in their chemical properties; it is currently unknown how these affect blood β-OHB and blood glucose compared to the ketone monoester. In a double-blind randomized cross-over pilot study, N=12 healthy individuals (29 ± 5 years, BMI = 25 ± 4 kg/m2, 42% female) participated in three experimental trials with a different ketone supplement providing 10 grams of active ingredient in each; (i) the monoester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, (ii) D-β-hydroxybutyric acid with R-1,3-butanediol, and (iii) R-1,3-butanediol. Blood β-OHB and glucose were measured via finger prick capillary blood samples at baseline and across 240 minutes post-supplementation. Supplement acceptability, hunger, and gastrointestinal distress were assessed via questionnaires. β-OHB was elevated compared to baseline in all conditions. Total and incremental area under the curve (p < 0.05) and peak β-OHB (p  < 0.001) differed between conditions with highest values seen in the ketone monoester condition. Blood glucose was reduced after consumption of each supplement, with no differences in total and incremental area under the curve across supplements. Supplement acceptability was greatest for D-β-hydroxybutyric acid with R-1,3-butanediol, with no effect on hunger or evidence of gastrointestinal distress across all supplements. All ketone supplements tested raised β-OHB with highest values seen after ketone monoester ingestion. Blood glucose was lowered similarly across the assessed time frame with all three supplements.

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.

Exogenous ketosis suppresses diuresis and atrial natriuretic peptide during exercise

We have previously demonstrated that exogenous ketosis reduces urine production during exercise. However, the underlying physiological mechanism of this anti-diuretic effect remained unclear. Therefore, we investigated whether acute exogenous ketosis by oral ingestion of ketone ester (KE) during a simulated cycling race (RACE) affects the hormonal pathways implicated in fluid balance regulation during exercise. In a double-blind crossover design, 11 well-trained male cyclists participated in RACE consisting of a 3-h submaximal intermittent cycling (IMT_180') bout followed by a 15-minute time trial (TT_15') in an environmental chamber set at 28 °C and 60 % relative humidity. Fluid intake was adjusted to maintain euhydration. Before and during RACE, the subjects received either a control drink (CON) or the ketone ester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KE), which elevated blood β-hydroxybutyrate to ~2-4 mM. Urine output during IMT_180' was ~20% lower in KE (1172 ± 557 ml) than in CON (1431 ± 548 ml, p < 0.05). Compared with CON, N-terminal pro-atrial natriuretic peptide (NT-pro ANP) concentration during RACE was ~20% lower in KE (p < 0.05). KE also raised plasma noradrenaline concentrations during RACE. Performance in TT_15' was similar between CON and KE. In conclusion, exogenous ketosis suppresses diuresis and downregulates α-natriuretic peptide activity during exercise.

Effects of Exogenous Ketone Supplementation on Blood Glucose: A Systematic Review and Meta-analysis

Recently developed ketone (monoester or salt) supplements acutely elevate blood β-hydroxybutyrate (BHB) exogenously without prolonged periods of fasting or carbohydrate restriction. Previous (small-scale) studies have found a blood glucose-lowering effect of exogenous ketones. This study aimed to systematically review available evidence and conduct meta-analyses of studies reporting on exogenous ketones and blood glucose. We searched 6 electronic databases on 13 December 2021 for randomized and nonrandomized trials of any length that reported on the use of exogenous ketones. We calculated raw mean differences (MDs) in blood BHB and glucose in 2 main analyses: 1) after compared with before acute ingestion of exogenous ketones and 2) following acute ingestion of exogenous ketones compared with a comparator supplement. We pooled effect sizes using random-effects models and performed prespecified subgroup analyses to examine the effect of potential explanatory factors, including study population, exercise, blood BHB, and supplement type, dosing, and timing. Risk of bias was examined using Cochrane's risk-of-bias tools. Studies that could not be meta-analyzed were summarized narratively. Forty-three trials including 586 participants are summarized in this review. Following ingestion, exogenous ketones increased blood BHB (MD = 1.73 mM; 95% CI: 1.26, 2.21 mM; P < 0.001) and decreased mean blood glucose (MD = -0.54 mM; 95% CI: -0.68, -0.40 mM; P < 0.001). Similarly, when compared with placebo, blood BHB increased (MD = 1.98 mM; 95% CI: 1.52, 2.45 mM; P < 0.001) and blood glucose decreased (MD = -0.47 mM; 95% CI: -0.57, -0.36 mM; P < 0.001). Across both analyses, significantly greater effects were seen with ketone monoesters compared with salts (P < 0.001). The available evidence indicates that acute ingestion of exogenous ketones leads to increased blood BHB and decreased blood glucose. Limited evidence on prolonged ketone supplementation was found.