Ketone Diester Ingestion Impairs Time-Trial Performance in Professional Cyclists

Skeletal muscle energy metabolism during exercise

The continual supply of ATP to the fundamental cellular processes that underpin skeletal muscle contraction during exercise is essential for sports performance in events lasting seconds to several hours. Because the muscle stores of ATP are small, metabolic pathways must be activated to maintain the required rates of ATP resynthesis. These pathways include phosphocreatine and muscle glycogen breakdown, thus enabling substrate-level phosphorylation ('anaerobic') and oxidative phosphorylation by using reducing equivalents from carbohydrate and fat metabolism ('aerobic'). The relative contribution of these metabolic pathways is primarily determined by the intensity and duration of exercise. For most events at the Olympics, carbohydrate is the primary fuel for anaerobic and aerobic metabolism. Here, we provide an overview of exercise metabolism and the key regulatory mechanisms ensuring that ATP resynthesis is closely matched to the ATP demand of exercise. We also summarize various interventions that target muscle metabolism for ergogenic benefit in athletic events.

In vitro ketone-supported mitochondrial respiration is minimal when other substrates are readily available in cardiac and skeletal muscle

KEY POINTS

Ketone bodies are proposed to represent an alternative fuel source driving energy production, particularly during exercise. Biologically, the extent to which mitochondria utilize ketone bodies compared to other substrates remains unknown. We demonstrate in vitro that maximal mitochondrial respiration supported by ketone bodies is low when compared to carbohydrate-derived substrates in the left ventricle and red gastrocnemius muscle from rodents, and in human skeletal muscle. When considering intramuscular concentrations of ketone bodies and the presence of other carbohydrate and lipid substrates, biological rates of mitochondrial respiration supported by ketone bodies are predicted to be minimal. At the mitochondrial level, it is therefore unlikely that ketone bodies are an important source for energy production in cardiac and skeletal muscle, particularly when other substrates are readily available.

ABSTRACT

Ketone bodies (KB) have recently gained popularity as an alternative fuel source to support mitochondrial oxidative phosphorylation and enhance exercise performance. However, given the low activity of ketolytic enzymes and potential inhibition from carbohydrate oxidation, it remains unknown if KBs can contribute to energy production. We therefore determined the ability of KBs (sodium dl-β-hydroxybutyrate, β-HB; lithium acetoacetate, AcAc) to stimulate in vitro mitochondrial respiration in the left ventricle (LV) and red gastrocnemius (RG) of rats, and in human vastus lateralis. Compared to pyruvate, the ability of KBs to maximally drive respiration was low in isolated mitochondria and permeabilized fibres (PmFb) from the LV (∼30-35% of pyruvate), RG (∼10-30%), and human vastus lateralis (∼2-10%). In PmFb, the concentration of KBs required to half-maximally drive respiration (LV: 889 µm β-HB, 801 µm AcAc; RG: 782 µm β-HB, 267 µm AcAc) were greater than KB content representative of the muscle microenvironment (∼100 µm). This would predict low rates (∼1-4% of pyruvate) of biological KB-supported respiration in the LV (8-14 pmol s^-1 mg^-1 ) and RG (3-6 pmol s^-1 mg^-1 ) at rest and following exercise. Moreover, KBs did not increase respiration in the presence of saturating pyruvate, submaximal pyruvate (100 µm) reduced the ability of physiological β-HB to drive respiration, and addition of other intracellular substrates (succinate + palmitoylcarnitine) decreased maximal KB-supported respiration. As a result, product inhibition is likely to limit KB oxidation. Altogether, the ability of KBs to drive mitochondrial respiration is minimal and they are likely to be outcompeted by other substrates, compromising their use as an important energy source.

No Benefit of Ingestion of a Ketone Monoester Supplement on 10-km Running Performance

PURPOSE

Preexercise ingestion of exogenous ketones alters the metabolic response to exercise, but effects on exercise performance have been equivocal.

METHODS

On two occasions in a double-blind, randomized crossover design, eight endurance-trained runners performed 1 h of submaximal exercise at approximately 65% V˙O2max immediately followed by a 10-km self-paced time trial (TT) on a motorized treadmill. An 8% carbohydrate-electrolyte solution was consumed before and during exercise, either alone (CHO + PLA), or with 573 mg·kg of a ketone monoester supplement (CHO + KME). Expired air, HR, and RPE were monitored during submaximal exercise. Serial venous blood samples were assayed for plasma glucose, lactate, and β-hydroxybutyrate concentrations.

RESULTS

CHO + KME produced plasma β-hydroxybutyrate concentrations of approximately 1.0 to 1.3 mM during exercise (P < 0.001), but plasma glucose and lactate concentrations were similar during exercise in both trials. V˙O2, running economy, respiratory exchange ratio, HR, and RPE were also similar between trials. Performance in the 10-km TT was not different (P = 0.483) between CHO + KME (mean, 2402 s; 95% confidence interval, 2204-2600 s) and CHO + PLA (mean, 2422 s; 95% confidence interval, 2217-2628 s). Cognitive performance, measured by reaction time and a multitasking test, did not differ between trials.

CONCLUSIONS

Compared with carbohydrate alone, coingestion of KME by endurance-trained athletes elevated plasma β-hydroxybutyrate concentrations, but did not improve 10-km running TT or cognitive performance.

Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible

INTRODUCTION

We repeated our study of intensified training on a ketogenic low-carbohydrate (CHO), high-fat diet (LCHF) in world-class endurance athletes, with further investigation of a "carryover" effect on performance after restoring CHO availability in comparison to high or periodised CHO diets.

METHODS

After Baseline testing (10,000 m IAAF-sanctioned race, aerobic capacity and submaximal walking economy) elite male and female race walkers undertook 25 d supervised training and repeat testing (Adapt) on energy-matched diets: High CHO availability (8.6 g∙kg-1∙d-1 CHO, 2.1 g∙kg-1∙d-1 protein; 1.2 g∙kg-1∙d-1 fat) including CHO before/during/after workouts (HCHO, n = 8): similar macronutrient intake periodised within/between days to manipulate low and high CHO availability at various workouts (PCHO, n = 8); and LCHF (<50 g∙d-1 CHO; 78% energy as fat; 2.1 g∙kg-1∙d-1 protein; n = 10). After Adapt, all athletes resumed HCHO for 2.5 wk before a cohort (n = 19) completed a 20 km race.

RESULTS

All groups increased VO2peak (ml∙kg-1∙min-1) at Adapt (p = 0.02, 95%CI: [0.35-2.74]). LCHF markedly increased whole-body fat oxidation (from 0.6 g∙min-1 to 1.3 g∙min-1), but also the oxygen cost of walking at race-relevant velocities. Differences in 10,000 m performance were clear and meaningful: HCHO improved by 4.8% or 134 s (95% CI: [207 to 62 s]; p < 0.001), with a trend for a faster time (2.2%, 61 s [-18 to +144 s]; p = 0.09) in PCHO. LCHF were slower by 2.3%, -86 s ([-18 to -144 s]; p < 0.001), with no evidence of superior "rebound" performance over 20 km after 2.5 wk of HCHO restoration and taper.

CONCLUSION

Our previous findings of impaired exercise economy and performance of sustained high-intensity race walking following keto-adaptation in elite competitors were repeated. Furthermore, there was no detectable benefit from undertaking an LCHF intervention as a periodised strategy before a 2.5-wk race preparation/taper with high CHO availability.

TRIAL REGISTRATION

Australia New Zealand Clinical Trial Registry: ACTRN12619000794101.

Exogenous ketosis impacts neither performance nor muscle glycogen breakdown in prolonged endurance exercise

Available evidence indicates that ketone bodies inhibit glycolysis in contracting muscles. Therefore, we investigated whether acute exogenous ketosis by oral ketone ester (KE) intake early in a simulated cycling race can induce transient glycogen sparing by glycolytic inhibition, thereby increasing glycogen availability in the final phase of the event. In a randomized crossover design, 12 highly trained male cyclists completed a simulated cycling race (RACE), which consisted of 3-h intermittent cycling (IMT_180′), a 15-min time trial (TT_15′), and a maximal sprint (SPRINT). During RACE, subjects received 60 g carbohydrates/h combined with three boluses (25, 20, and 20 g) (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KE) or a control drink (CON) at 60 and 20 min before and at 30 min during RACE. KE intake transiently increased blood d-β-hydroxybutyrate to ~3 mM (range: 2.6–5.2 mM) during the first half of RACE (P < 0.001 vs. CON). Blood pH concomitantly decreased from approximately 7.42 to 7.36 (range: 7.29–7.40), whereas bicarbonate dropped from 26.0 to 21.6 mM (range: 20.1–23.7; both P < 0.001 vs. CON)_. Net muscle glycogen breakdown during IMT_180′ [KE: −78 ± 30 (SD); CON: −60 ± 22 mmol/kg wet wt; P = 0.08] and TT_15′ (KE: −9 ± 18; CON: −18 ± 18 mmol/kg wet wt; P = 0.35) was similar between KE and CON. Accordingly, mean power output during TT_15′ (KE: 273 ± 38; CON: 272 ± 37 W; P = 0.83) and time-to-exhaustion in the SPRINT (KE: 59 ± 16; CON: 58 ± 17 s; P = 0.66) were similar between conditions. In conclusion, KE intake during a simulated cycling race does not cause glycogen sparing, nor does it affect all-out performance in the final stage of a simulated race.

NEW & NOTEWORTHY Exogenous ketosis produced by oral ketone ester ingestion during the early phase of prolonged endurance exercise and against the background of adequate carbohydrate intake neither causes muscle glycogen sparing nor improves performance in the final stage of the event. However, such exogenous ketosis may decrease buffering capacity in the approach of the final episode of the event. Furthermore, ketone ester intake during exercise may reduce appetite immediately after exercise.

A Pre-Workout Supplement of Ketone Salts, Caffeine, and Amino Acids Improves High-Intensity Exercise Performance in Keto-Naïve and Keto-Adapted Individuals

Background: Acute ingestion of ketone supplements alters metabolism and potentially exercise performance. No studies to date have evaluated the impact of co-ingestion of ketone salts with caffeine and amino acids on high intensity exercise performance, and no data exists in Keto-Adapted individuals.Methods: We tested the performance and metabolic effects of a pre-workout supplement containing beta-hydroxybutyrate (BHB) salts, caffeine, and amino acids (KCA) in recreationally-active adults habitually consuming a mixed diet (Keto-Naïve; n = 12) or a ketogenic diet (Keto-Adapted; n = 12). In a randomized and balanced manner, subjects consumed either the KCA consisting of ∼7 g BHB (72% R-BHB and 28% S-BHB) with ∼100 mg of caffeine, and amino acids (leucine and taurine) or Water (control condition) 15 minutes prior to performing a staged cycle ergometer time to exhaustion test followed immediately by a 30 second Wingate test.Results: Circulating total BHB concentrations increased rapidly after KCA ingestion in KN (154 to 732 μM) and KA (848 to 1,973 μM) subjects and stayed elevated throughout recovery in both groups. Plasma S-BHB increased >20-fold 15 minutes after KCA ingestion in both groups and remained elevated throughout recovery. Compared to Water, KCA ingestion increased time to exhaustion 8.3% in Keto-Naïve and 9.8% in Keto-Adapted subjects (P < 0.001). There was no difference in power output during the Wingate test between trials. Peak lactate immediately after exercise was higher after KCA (∼14.9 vs 12.7 mM).Conclusion: These results indicate that pre-exercise ingestion of a moderate dose of R- and S-BHB salts combined with caffeine, leucine and taurine improves high-intensity exercise performance to a similar extent in both Keto-Adapted and Keto-Naïve individuals.

Effects of an Exogenous Ketone Supplement on Five-Kilometer Running Performance

Numerous oral ketone supplements are marketed with the claim that they will rapidly induce ketosis and improve exercise performance. The purpose of this study was to assess exercise performance time and related physiological, metabolic and perceptual responses of recreational endurance runners after ingestion of a commercially available oral ketone supplement. Recreational endurance runners (n = 10; age: 20.8 ± 1.0 years; body mass: 68.9 ± 5.6 kg; height: 175.6 ± 4.9 cm) participated in a double-blind, crossover, repeated-measures study where they were randomized to 300 mg.kg-1 body weight of an oral β-hydroxybutyrate-salt + Medium Chain Triglyceride (βHB-salt+MCT) ketone supplement or a flavor matched placebo (PLA) 60 min prior to performing a 5-km running time trial (5KTT) on a treadmill. Time, HR, RPE, affect, RER, VO₂, VCO₂, and VE were measured during the 5-km run. The Session RPE and affect (Feeling Scale) were obtained post-5KTT. Plasma glucose, lactate and ketones were measured at baseline, 60-min post-supplement, and immediately post-5KTT. Plasma R-βHB (endogenous isomer) was elevated from baseline and throughout the entire protocol under the βHB-salt+MCT condition (p < 0.05). No significant difference (58.3 ± 100.40 s; 95% CI: -130.12 – 13.52; p = 0.100) was observed between the βHB-salt+MCT supplement (1430.0 ± 187.7 s) and the PLA (1488.3 ± 243.8 s) in time to complete the 5KTT. No other differences (p > 0.05) were noted in any of the other physiological, metabolic or perceptual measures.

Exogenous Ketone Salts Do Not Improve Cognitive Performance During a Dual-Stress Challenge

In the present study, our team aimed to investigate the effects of acute ingestion of a ketone salt (KS) supplement on the cognitive performance in healthy college-aged males during a dual-stress challenge (DSC). Following a peak oxygen uptake test and DSC familiarization, 16 males completed a DSC while cycling at 60% of their respective peak oxygen uptake after ingesting either a commercially available racemic (D- andL-)β-hydroxybutyrate (β-OHB) KS (0.38 g/kg body mass) or a placebo, using a triple-blinded, crossover, and counterbalanced design. The participants consumed the KS or placebo at −60 and −15 min prior to the start of the DSC. Heart rate, rating of perceived exertion, and blood β-OHB and glucose were sampled throughout. The DSC consisted of a mental arithmetic challenge and a modified Stroop Color Word, which alternated every 2 min for 20 min. Upon completion of the DSC, responses for correct, incorrect, and no responses were recorded for the mental arithmetic challenge and Stroop Color Word. Blood β-OHB was elevated with KS by −15 min and remained so throughout (p < .001), peaking at 0.76 ± 0.32 mM. Blood glucose was lower with KS compared with the placebo at −15 and 10 min by 9% and 5%, respectively (bothps < .05). There were no differences between the treatments for heart rate, rating of perceived exertion, mental arithmetic challenge, or Stroop Color Word. Overall, this study suggests that KSs are not effective aids for enhancing cognitive performance during a DSC, which might partially be explained by the inability of currently available commercial KS supplements to elevate β-OHB blood concentrations above ∼1.0 mM.

Utility of Ketone Supplementation to Enhance Physical Performance: A Systematic Review

Ingesting exogenous ketone bodies has been touted as producing ergogenic effects by altering substrate metabolism; however, research findings from recent studies appear inconsistent. This systematic review aimed to aggregate data from the current literature to examine the impact of consuming ketone supplements on enhancing physical performance. A systematic search was performed for randomized controlled trials that measured physical performance outcomes in response to ingesting exogenous ketone supplements compared with a control (nutritive or non-nutritive) in humans. A total of 161 articles were screened. Data were extracted from 10 eligible studies (112 participants; 109 men, 3 women ) containing 16 performance outcomes [lower-body power (n = 8) and endurance performance (n = 8)]. Ketone supplements were grouped as ketone esters (n = 8) or ketone salts/precursors (n = 8). Of the 16 performance outcomes identified by the systematic review, 3 reported positive, 10 reported null, and 3 reported negative effects of ketone supplementation on physical performance compared with controls. Heterogeneity was detected for lower-body power ( Q = 40, I2 = 83%, P < 0.01) and endurance performance (Q = 95, I2 = 93%, P < 0.01) between studies. Similarly high levels of heterogeneity were detected in studies providing ketone esters (Q = 111, I2 = 93%, P < 0.01), and to a lesser extent studies with ketone salts/precursors (Q = 25, I2 = 72%, P < 0.01). Heterogeneity across studies makes it difficult to conclude any benefit or detriment to consuming ketone supplements on physical performance. This systematic review discusses factors within individual studies that may contribute to discordant outcomes across investigations to elucidate if there is sufficient evidence to warrant recommendation of consuming exogenous ketone supplements to enhance physical performance.

Acute Ketone Supplementation and Exercise Performance: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

PURPOSE

To determine the acute effects of ketone supplementation on exercise performance (primary outcome) and physiological and perceptual responses to exercise (secondary outcomes).

METHODS

A systematic search was conducted in PubMed, Web of Science, and SPORTDiscus (since inception to July 21, 2019) to find randomized controlled trials assessing the effects of acute ketone supplementation compared with a drink containing no ketones (ie, control intervention). The standardized mean difference (Hedges g) between interventions and 95% confidence interval (CI) were computed using a random-effects model.

RESULTS

Thirteen studies met all inclusion criteria. No significant differences were observed between interventions for overall exercise performance (Hedges g = -0.05; 95% CI, -0.30 to 0.20; P = .68). Subanalyses revealed no differences between interventions when analyzing endurance time-trial performance (g = -0.04; 95% CI, -0.35 to 0.28; P = .82) or when assessing the separate effects of supplements containing ketone esters (g = -0.07; 95% CI, -0.38 to 0.24; P = .66) or salts (g = -0.02; 95% CI, -0.45 to 0.41; P = .93). All studies reported increases in plasma ketone concentration after acute ketone supplementation, but no consistent effects were reported on the metabolic (plasma lactate and glucose levels), respiratory (respiratory exchange ratio, oxygen uptake, and ventilatory rate), cardiovascular (heart rate), or perceptual responses to exercise (rating of perceived exertion).

CONCLUSIONS

The present findings suggest that ketone supplementation exerts no clear influence on exercise performance (from sprints to events lasting up to ∼50 min) or metabolic, respiratory, cardiovascular, or perceptual responses to exercise. More research is needed to elucidate if this strategy could provide ergogenic effects on other exercise types (eg, ultraendurance exercise).

Impact of ketosis on appetite regulation-a review

To reduce the health burden of obesity, it is important to identify safe and practical treatments that are effective for weight loss while concurrently preventing weight regain. Diet-induced weight loss is usually followed by a concomitant increase in ghrelin secretion and feelings of hunger, which may compromise weight loss goals and increase the risk of weight regain. The aim of this review is to describe the status of knowledge regarding the impact of ketosis, induced by diet or exogenous ketones (ketone esters), on appetite and the potential mechanisms involved. Ketogenic diets (KDs) have been shown to prevent an increase in ghrelin secretion, otherwise seen with weight loss, as well as to reduce hunger and/or prevent hunger. However, the exact threshold of ketosis needed to induce appetite suppression, as well as the exact mechanisms that mediate such an effect, has yet to be elucidated. Use of exogenous ketones may provide an alternative to KDs, which have poor long-term adherence due to their restrictive nature. Ketone esters have been shown to have concentration-dependent effects on food intake and body weight in rodent models, with effects becoming apparent when 30% of total dietary energy comes from ketone esters (threshold effect). In humans, acute consumption of a ketone ester drink reduced feelings of hunger and increased satiety compared to a dextrose drink. With the emerging widespread acceptance of KDs and exogenous ketones in mainstream media and the diet culture, it is important to fully understand their role on appetite control and weight management and the potential mechanisms mediating this role.

Acute hyperketonaemia alters T-cell-related cytokine gene expression within stimulated peripheral blood mononuclear cells following prolonged exercise

PURPOSE

We investigated the effect of the racemic β-hydroxybutyrate precursor, R,S-1,3-butanediol (BD), on T-cell-related cytokine gene expression within stimulated peripheral blood mononuclear cells (PBMC) following prolonged, strenuous exercise.

METHODS

A repeated-measures, randomised, crossover study was conducted in nine healthy, trained male cyclists (age, 26.7 ± 5.2 years; VO_2peak, 63.9 ± 2.5 mL kg^-1 min^-1). Participants ingested 0.35 g kg^-1 of BD or placebo 30 min before and 60 min during 85 min of steady-state (SS) exercise, which preceded a ~ 30 min time-trial (TT) (7 kJ kg^-1). Blood samples were collected at pre-supplement, pre-exercise, post-SS, post-TT and 1-h post-TT. Whole blood cultures were stimulated with Staphylococcal enterotoxin B (SEB) for 24 h to determine T-cell-related interleukin (IL)-4, IL-10 and interferon (IFN)-γ mRNA expression within isolated PBMCs in vitro.

RESULTS

Serum cortisol, total circulating leukocyte and lymphocyte, and T-cell subset concentrations were similar between trials during exercise and recovery (all p > 0.05). BD ingestion increased T-cell-related IFN-γ mRNA expression compared with placebo throughout exercise and recovery (p = 0.011); however, IL-4 and IL-10 mRNA expression and the IFN-γ/IL-4 mRNA expression ratio were unaltered (all p > 0.05).

CONCLUSION

Acute hyperketonaemia appears to transiently amplify the initiation of the pro-inflammatory T-cell-related IFN-γ response to an immune challenge in vitro during and following prolonged, strenuous exercise; suggesting enhanced type-1 T-cell immunity at the gene level.

International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing

Background

In this Position Statement, the International Society of Sports Nutrition (ISSN) provides an objective and critical review of the literature pertinent to nutritional considerations for training and racing in single-stage ultra-marathon. Recommendations for Training. i) Ultra-marathon runners should aim to meet the caloric demands of training by following an individualized and periodized strategy, comprising a varied, food-first approach; ii) Athletes should plan and implement their nutrition strategy with sufficient time to permit adaptations that enhance fat oxidative capacity; iii) The evidence overwhelmingly supports the inclusion of a moderate-to-high carbohydrate diet (i.e., ~ 60% of energy intake, 5–8 g·kg^− 1·d^− 1) to mitigate the negative effects of chronic, training-induced glycogen depletion; iv) Limiting carbohydrate intake before selected low-intensity sessions, and/or moderating daily carbohydrate intake, may enhance mitochondrial function and fat oxidative capacity. Nevertheless, this approach may compromise performance during high-intensity efforts; v) Protein intakes of ~ 1.6 g·kg^− 1·d^− 1 are necessary to maintain lean mass and support recovery from training, but amounts up to 2.5 g.kg^− 1·d^− 1 may be warranted during demanding training when calorie requirements are greater; Recommendations for Racing. vi) To attenuate caloric deficits, runners should aim to consume 150–400 Kcal·h^− 1 (carbohydrate, 30–50 g·h^− 1; protein, 5–10 g·h^− 1) from a variety of calorie-dense foods. Consideration must be given to food palatability, individual tolerance, and the increased preference for savory foods in longer races; vii) Fluid volumes of 450–750 mL·h^− 1 (~ 150–250 mL every 20 min) are recommended during racing. To minimize the likelihood of hyponatraemia, electrolytes (mainly sodium) may be needed in concentrations greater than that provided by most commercial products (i.e., > 575 mg·L^− 1 sodium). Fluid and electrolyte requirements will be elevated when running in hot and/or humid conditions; viii) Evidence supports progressive gut-training and/or low-FODMAP diets (fermentable oligosaccharide, disaccharide, monosaccharide and polyol) to alleviate symptoms of gastrointestinal distress during racing; ix) The evidence in support of ketogenic diets and/or ketone esters to improve ultra-marathon performance is lacking, with further research warranted; x) Evidence supports the strategic use of caffeine to sustain performance in the latter stages of racing, particularly when sleep deprivation may compromise athlete safety.

Gastrointestinal Effects of Exogenous Ketone Drinks are Infrequent, Mild, and Vary According to Ketone Compound and Dose

Exogenous ketone drinks may improve athletic performance and recovery, but information on their gastrointestinal tolerability is limited. Studies to date have used a simplistic reporting methodology that inadequately represents symptom type, frequency, and severity. Herein, gastrointestinal symptoms were recorded during three studies of exogenous ketone monoester (KME) and salt (KS) drinks. Study 1 compared low- and high-dose KME and KS drinks consumed at rest. Study 2 compared KME with isocaloric carbohydrate (CHO) consumed at rest either when fasted or after a standard meal. Study 3 compared KME+CHO with isocaloric CHO consumed before and during 3.25 hr of bicycle exercise. Participants reported symptom type and rated severity between 0 and 8 using a Likert scale at regular intervals. The number of visits with no symptoms reported after ketone drinks was n = 32/60 in Study 1, n = 9/32 in Study 2, and n = 20/42 in Study 3. Following KME and KS drinks, symptoms were acute but mild and were fully resolved by the end of the study. High-dose KS drinks caused greater total-visit symptom load than low-dose KS drinks (13.8 ± 4.3 vs. 2.0 ± 1.0; p < .05) and significantly greater time-point symptom load than KME drinks 1–2 hr postdrink. At rest, KME drinks caused greater total-visit symptom load than CHO drinks (5.0 ± 1.6 vs. 0.6 ± 0.4; p < .05). However, during exercise, there was no significant difference in total-visit symptom load between KME+CHO (4.2 ± 1.0) and CHO (7.2 ± 1.9) drinks. In summary, exogenous ketone drinks cause mild gastrointestinal symptoms that depend on time, the type and amount of compound consumed, and exercise.

Ketone Administration for Seizure Disorders: History and Rationale for Ketone Esters and Metabolic Alternatives

The ketogenic diet (KD) is a high-fat, low-carbohydrate treatment for medically intractable epilepsy. One of the hallmark features of the KD is the production of ketone bodies which have long been believed, but not yet proven, to exert direct anti-seizure effects. The prevailing view has been that ketosis is an epiphenomenon during KD treatment, mostly due to clinical observations that blood ketone levels do not correlate well with seizure control. Nevertheless, there is increasing experimental evidence that ketone bodies alone can exert anti-seizure properties through a multiplicity of mechanisms, including but not limited to: (1) activation of inhibitory adenosine and ATP-sensitive potassium channels; (2) enhancement of mitochondrial function and reduction in oxidative stress; (3) attenuation of excitatory neurotransmission; and (4) enhancement of central γ-aminobutyric acid (GABA) synthesis. Other novel actions more recently reported include inhibition of inflammasome assembly and activation of peripheral immune cells, and epigenetic effects by decreasing the activity of histone deacetylases (HDACs). Collectively, the preclinical evidence to date suggests that ketone administration alone might afford anti-seizure benefits for patients with epilepsy. There are, however, pragmatic challenges in administering ketone bodies in humans, but prior concerns may largely be mitigated through the use of ketone esters or balanced ketone electrolyte formulations that can be given orally and induce elevated and sustained hyperketonemia to achieve therapeutic effects.

Exogenous Ketones Lower Blood Glucose Level in Rested and Exercised Rodent Models

Diseases involving inflammation and oxidative stress can be exacerbated by high blood glucose levels. Due to tight metabolic regulation, safely reducing blood glucose can prove difficult. The ketogenic diet (KD) reduces absolute glucose and insulin, while increasing fatty acid oxidation, ketogenesis, and circulating levels of β-hydroxybutyrate (βHB), acetoacetate (AcAc), and acetone. Compliance to KD can be difficult, so alternative therapies that help reduce glucose levels are needed. Exogenous ketones provide an alternative method to elevate blood ketone levels without strict dietary requirements. In this study, we tested the changes in blood glucose and ketone (βHB) levels in response to acute, sub-chronic, and chronic administration of various ketogenic compounds in either a post-exercise or rested state. WAG/Rij (WR) rats, a rodent model of human absence epilepsy, GLUT1 deficiency syndrome mice (GLUT1D), and wild type Sprague Dawley rats (SPD) were assessed. Non-pathological animals were also assessed across different age ranges. Experimental groups included KD, standard diet (SD) supplemented with water (Control, C) or with exogenous ketones: 1, 3-butanediol (BD), βHB mineral salt (KS), KS with medium chain triglyceride/MCT (KSMCT), BD acetoacetate diester (KE), KE with MCT (KEMCT), and KE with KS (KEKS). In rested WR rats, the KE, KS, KSMCT groups had lower blood glucose level after 1 h of treatment, and in KE and KSMCT groups after 24 h. After exercise, the KE, KSMCT, KEKS, and KEMCT groups had lowered glucose levels after 1 h, and in the KEKS and KEMCT groups after 7 days, compared to control. In GLUT1D mice without exercise, only KE resulted in significantly lower glucose levels at week 2 and week 6 during a 10 weeks long chronic feeding study. In 4-month and 1-year-old SPD rats in the post-exercise trials, blood glucose was significantly lower in KD and KE, and in KEMCT groups, respectively. After seven days, the KSMCT group had the most significantly reduced blood glucose levels, compared to control. These results indicate that exogenous ketones were efficacious in reducing blood glucose levels within and outside the context of exercise in various rodent models of different ages, with and without pathology.

Ketogenic Diets and Exercise Performance

The ketogenic diet (KD) has gained a resurgence in popularity due to its purported reputation for fighting obesity. The KD has also acquired attention as an alternative and/or supplemental method for producing energy in the form of ketone bodies. Recent scientific evidence highlights the KD as a promising strategy to treat obesity, diabetes, and cardiac dysfunction. In addition, studies support ketone body supplements as a potential method to induce ketosis and supply sustainable fuel sources to promote exercise performance. Despite the acceptance in the mainstream media, the KD remains controversial in the medical and scientific communities. Research suggests that the KD or ketone body supplementation may result in unexpected side effects, including altered blood lipid profiles, abnormal glucose homeostasis, increased adiposity, fatigue, and gastrointestinal distress. The purpose of this review article is to provide an overview of ketone body metabolism and a background on the KD and ketone body supplements in the context of obesity and exercise performance. The effectiveness of these dietary or supplementation strategies as a therapy for weight loss or as an ergogenic aid will be discussed. In addition, the recent evidence that indicates ketone body metabolism is a potential target for cardiac dysfunction will be reviewed.

The Effect of 1,3-Butanediol on Cycling Time-Trial Performance

This study investigated the effect of the racemic β-hydroxybutyrate (βHB) precursor, R,S-1,3-butanediol (BD), on time-trial (TT) performance and tolerability. A repeated-measures, randomized, crossover study was conducted in nine trained male cyclists (age, 26.7 ± 5.2 years; body mass, 69.6 ± 8.4 kg; height, 1.82 ± 0.09 m; body mass index, 21.2 ± 1.5 kg/m2; VO2peak,63.9 ± 2.5 ml·kg−1·min−1; Wmax, 389.3 ± 50.4 W). Participants ingested 0.35 g/kg of BD or placebo 30 min before and 60 min during 85 min of steady-state exercise, which preceded a ∼25- to 35-min TT (i.e., 7 kJ/kg). The ingestion of BD increased blood D-βHB concentration throughout exercise (0.44–0.79 mmol/L) compared with placebo (0.11–0.16 mmol/L; all p < .001), which peaked 1 hr following the TT (1.38 ± 0.35 vs. 0.34 ± 0.24 mmol/L; p < .001). Serum glucose and blood lactate concentrations were not different between trials (all p > .05). BD ingestion increased oxygen consumption and carbon dioxide production after 20 min of steady-state exercise (p = .002 and p = .032, respectively); however, no further effects on cardiorespiratory parameters were observed. Within the BD trial, moderate to severe gastrointestinal symptoms were reported in five participants, and low levels of dizziness, nausea, and euphoria were reported in two participants. However, this had no effect on TT duration (placebo, 28.5 ± 3.6 min; BD, 28.7 ± 3.2 min; p = .62) and average power output (placebo, 290.1 ± 53.7 W; BD, 286.4 ± 45.9 W; p = .50). These results suggest that BD has no benefit for endurance performance.

Dietary Neuroketotherapeutics for Alzheimer's Disease: An Evidence Update and the Potential Role for Diet Quality

Alzheimer’s disease (AD) is a devastating neurodegenerative disease with growing prevalence as the global population ages. Currently available treatments for AD have minimal efficacy and there are no proven treatments for its prodrome, mild cognitive impairment (MCI). AD etiology is not well understood and various hypotheses of disease pathogenesis are currently under investigation. A consistent hallmark in patients with AD is reduced brain glucose utilization; however, evidence suggests that brain ketone metabolism remains unimpaired, thus, there is a great deal of increased interest in the potential value of ketone-inducing therapies for the treatment of AD (neuroketotherapeutics; NKT). The goal of this review was to discuss dietary NKT approaches and mechanisms by which they exert a possible therapeutic benefit, update the evidence available on NKTs in AD and consider a potential role of diet quality in the clinical use of dietary NKTs. Whether NKTs affect AD symptoms through the restoration of bioenergetics, the direct and indirect modulation of antioxidant and inflammation pathways, or both, preliminary positive evidence suggests that further study of dietary NKTs as a disease-modifying treatment in AD is warranted.

Ketone body therapy with D/L-β-hydroxybutyric acid solution in severe MADD

Objectives

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a severe inborn disorder of mitochondrial fatty acid oxidation. The only treatment option for MADD is the use of exogenous ketone bodies, like sodium β-hydroxybutyrate (NaβHB). However, the use of ketone body salts leads to a high intake of accompanying minerals, which can lead to additional side effects. The use of mineral-free formulations could improve tolerability.

Methods

In this report, the use of a βHB acid (βHBA) in a patient with MADD is described. The production of D/L-βHBA was carried out using ion exchange chromatography (IEX) and using a precipitation method. During two inpatient treatment intervals, the tolerability as well as clinical and metabolic effects were monitored. D-βHB in serum, blood gas analysis, and standard blood measurements (like minerals) were used as control parameters.

Results

Production of D/L-βHBA using the precipitation method was more effective than using IEX. The tube feed solution used had a minimum pH of 3.5. Capillary D-βHB measurements were between 0.1 and 0.4 mmol/L and venous were at 0.1 mmol/L or below. Minerals and serum pH were within the normal range. During application of D/L-βHBA, gastrointestinal discomfort occurred and no clinical improvement was observed.

Conclusions

The use of D/L-βHBA in the therapy of severe MADD could be a good addition to the use of classical ketone body salts. The observed gastrointestinal side effects were of a mild nature and could not be specifically attributed to the D/L-βHBA treatment. In short-term application, no clinical benefit and no substantial increase of D-βHB in serum were noted. No tendency towards acidosis or alkalosis was observed during the entire period of treatment.

'I think I'm gonna hurl': A Narrative Review of the Causes of Nausea and Vomiting in Sport

Exercise-associated gastrointestinal (GI) distress can negatively impact athletic performance and interfere with exercise training. Although there are a few universal underlying causes of GI distress, each symptom often has its own unique triggers and, therefore, its own prevention and management strategies. One of the most troubling GI symptoms an athlete can experience during training and competition is nausea/vomiting. The prevalence of nausea varies with several factors, two of the most important being exercise intensity and duration. Relatively brief, high-intensity exercise (e.g., sprinting, tempo runs) and ultra-endurance exercise are both associated with more frequent and severe nausea. The potential causes of nausea in sport are numerous and can include catecholamine secretion, hypohydration, heat stress, hyponatremia, altitude exposure, excessive fluid/food consumption, hypertonic beverage intake, pre-exercise intake of fatty- or protein-rich foods (especially in close proximity to exercise), prolonged fasting, various supplements (caffeine, sodium bicarbonate, ketones), certain drugs (antibiotics, opioids), GI infections, and competition-related anxiety. Beyond directly addressing these aforementioned causes, antiemetic drugs (e.g., ondansetron) may also be useful for alleviating nausea in some competitive situations. Given the commonness of nausea in sport and its potential impact on exercise performance, athletes and sports medicine practitioners should be aware of the origins of nausea and strategies for dealing with this troublesome gut complaint.

Ketone ester supplementation blunts overreaching symptoms during endurance training overload

KEY POINTS

Overload training is required for sustained performance gain in athletes (functional overreaching). However, excess overload may result in a catabolic state which causes performance decrements for weeks (non-functional overreaching) up to months (overtraining). Blood ketone bodies can attenuate training- or fasting-induced catabolic events. Therefore, we investigated whether increasing blood ketone levels by oral ketone ester (KE) intake can protect against endurance training-induced overreaching. We show for the first time that KE intake following exercise markedly blunts the development of physiological symptoms indicating overreaching, and at the same time significantly enhances endurance exercise performance. We provide preliminary data to indicate that growth differentiation factor 15 (GDF15) may be a relevant hormonal marker to diagnose the development of overtraining. Collectively, our data indicate that ketone ester intake is a potent nutritional strategy to prevent the development of non-functional overreaching and to stimulate endurance exercise performance.

ABSTRACT

It is well known that elevated blood ketones attenuate net muscle protein breakdown, as well as negate catabolic events, during energy deficit. Therefore, we hypothesized that oral ketones can blunt endurance training-induced overreaching. Fit male subjects participated in two daily training sessions (3 weeks, 6 days/week) while receiving either a ketone ester (KE, n = 9) or a control drink (CON, n = 9) following each session. Sustainable training load in week 3 as well as power output in the final 30 min of a 2-h standardized endurance session were 15% higher in KE than in CON (both P < 0.05). KE inhibited the training-induced increase in nocturnal adrenaline (P < 0.01) and noradrenaline (P < 0.01) excretion, as well as blunted the decrease in resting (CON: -6 ± 2 bpm; KE: +2 ± 3 bpm, P < 0.05), submaximal (CON: -15 ± 3 bpm; KE: -7 ± 2 bpm, P < 0.05) and maximal (CON: -17 ± 2 bpm; KE: -10 ± 2 bpm, P < 0.01) heart rate. Energy balance during the training period spontaneously turned negative in CON (-2135 kJ/day), but not in KE (+198 kJ/day). The training consistently increased growth differentiation factor 15 (GDF15), but ∼2-fold more in CON than in KE (P < 0.05). In addition, delta GDF15 correlated with the training-induced drop in maximal heart rate (r = 0.60, P < 0.001) and decrease in osteocalcin (r = 0.61, P < 0.01). Other measurements such as blood ACTH, cortisol, IL-6, leptin, ghrelin and lymphocyte count, and muscle glycogen content did not differentiate KE from CON. In conclusion, KE during strenuous endurance training attenuates the development of overreaching. We also identify GDF15 as a possible marker of overtraining.

Dietary Fuels in Athletic Performance

Focusing on daily nutrition is important for athletes to perform and adapt optimally to exercise training. The major roles of an athlete's daily diet are to supply the substrates needed to cover the energy demands for exercise, to ensure quick recovery between exercise bouts, to optimize adaptations to exercise training, and to stay healthy. The major energy substrates for exercising skeletal muscles are carbohydrate and fat stores. Optimizing the timing and type of energy intake and the amount of dietary macronutrients is essential to ensure peak training and competition performance, and these strategies play important roles in modulating skeletal muscle adaptations to endurance and resistance training. In this review, recent advances in nutritional strategies designed to optimize exercise-induced adaptations in skeletal muscle are discussed, with an emphasis on mechanistic approaches, by describing the physiological mechanisms that provide the basis for different nutrition regimens.

Exogenous Ketone Bodies as Promising Neuroprotective Agents for Developmental Brain Injury

Ketone bodies are a promising area of neuroprotection research that may be ideally suited to the injured newborn. During normal development, the human infant is in significant ketosis for at least the first week of life. Ketone uptake and metabolism is upregulated in the both the fetus and neonate, with ketone bodies providing at least 10% of cerebral metabolic energy requirements, as well as being the preferred precursors for the synthesis of fatty acids and cholesterol. At the same time, ketone bodies have been shown to have multiple neuroprotective effects, including being anticonvulsant, decreasing oxidative stress and inflammation, and epigenetically upregulating the production of neurotrophic factors. While ketogenic diets and exogenous ketosis are largely being investigated in the setting of adult brain injury, the adaptation of the neonate to ketosis suggests that developmental brain injury may be the area most suited to the use of ketones for neuroprotection. Here, we describe the mechanisms by which ketone bodies exert their neuroprotective effects, and how these may translate to benefits within each of the phases of neonatal asphyxial brain injury.

Intermittent Running and Cognitive Performance after Ketone Ester Ingestion

PURPOSE

Ingestion of exogenous ketones alters the metabolic response to exercise and may improve exercise performance, but it has not been explored in variable-intensity team sport activity, or for effects on cognitive function.

METHODS

On two occasions in a double-blind, randomized crossover design, 11 male team sport athletes performed the Loughborough Intermittent Shuttle Test (part A, 5 × 15-min intermittent running; part B, shuttle run to exhaustion), with a cognitive test battery before and after. A 6.4% carbohydrate-electrolyte solution was consumed before and during exercise either alone (PLA) or with 750 mg·kg of a ketone ester (KE) supplement. Heart rate, RPE, and 15-m sprint times were recorded throughout, and serial venous blood samples were assayed for plasma glucose, lactate, and β-hydroxybutyrate.

RESULTS

KE resulted in plasma β-hydroxybutyrate concentrations of ~1.5 to 2.6 mM during exercise (P < 0.001). Plasma glucose and lactate concentrations were lower during KE compared with PLA (moderate-to-large effect sizes). Heart rate, RPE, and 15-m sprint times did not differ between trials. Run time to exhaustion was not different (P = 0.126, d = 0.45) between PLA (mean = 268 s, 95% confidence interval [CI] = 199-336 s) and KE (mean = 229 s, 95% CI = 178-280 s). Incorrect responses in a multitasking test increased from pre- to postexercise in PLA (mean = 1.8, 95% CI = -0.6 to 4.1) but not in KE (mean = 0.0, 95% CI = -1.8 to 1.8) (P = 0.017, d = 0.70).

CONCLUSION

Compared with carbohydrate alone, coingestion of a KE by team sport athletes attenuated the rise in plasma lactate concentrations but did not improve shuttle run time to exhaustion or 15-m sprint times during intermittent running. An attenuation of the decline in executive function after exhausting exercise suggests a cognitive benefit after KE ingestion.

Effects of β-hydroxybutyrate treatment on glycogen repletion and its related signaling cascades in epitrochlearis muscle during 120 min of postexercise recovery

We investigated the effects of β-hydroxybutyrate (β-HB), the most abundant type of ketone body in mammals, on postexercise glycogen recovery in skeletal muscle by using an in vitro experimental model. Male ICR mice swam for 60 min and then their epitrochlearis muscles were removed and incubated with either physiological levels of glucose (8 mmol/L) and insulin (60 μU/mL) or glucose and insulin plus 1, 2, or 4 mmol/L of sodium β-HB. Four millimoles per liter β-HB had a significant positive effect on glycogen repletion in epitrochlearis muscle at 120 min after exercise (p < 0.01), while 2 mmol/L of β-HB showed a tendency to increase the glycogen level (p < 0.09), and 1 mmol/L of β-HB had no significant effect. We further investigated the effect of 4 mmol/L β-HB treatment on the signaling cascade related to glycogen repletion in the epitrochlearis muscles throughout a 120-min recovery period. After incubating the muscles in 4 mmol/L of β-HB for 15 min postexercise, the Akt substrate of 160 kDa Thr⁶⁴² (p < 0.05) and Akt Thr³⁰⁸ (p < 0.05) phosphorylations were significantly increased compared with the control treatment. At the same time point, 5'-AMP-activated protein kinase and acetyl-coenzyme A carboxylase phosphorylations were significantly lower (p < 0.05) in the epitrochlearis muscle incubated with 4 mmol/L of β-HB than in the control muscle. Our results demonstrate that postexercise 4 mmol/L β-HB administration enhanced glycogen repletion in epitrochlearis muscle. Four millimoles per liter β-HB treatment was associated with alternation of the phosphorylated status of several proteins involved in glucose uptake and metabolic/energy homeostasis at the early stage of postexercise.

Effect of a four-week ketogenic diet on exercise metabolism in CrossFit-trained athletes

BACKGROUND

The ketogenic diet is becoming a popular nutritional model among athletes. However, the relationship between its use and metabolism during exercise seems to have not been fully investigated.

METHODS

The aim of the study was to assess the effects of a four-week ketogenic diet (KD) on fat and carbohydrate (CHO) utilization during an incremental cycling test (ICT) in CrossFit-trained female (n = 11) and male (n = 11) athletes. During the ICT (while consuming the customary diet and after the KD), oxygen uptake and carbon dioxide exhalation were registered, and CHO and fat utilization as well as energy expenditure were calculated.

RESULTS

In males, the KD led to an increase in fat utilization (g·min- 1·kgFFM- 1 and % oxidation). It was particularly noticeable at exercise intensities up to 80% of VO2max. An increase in the area under the curve (AUC) was seen in males but not in females at up to ≤65% VO2max of fat utilization.

CONCLUSIONS

Male CrossFit-trained athletes seem to be more prone to shifts in macronutrient utilization (in favor of fat utilization) during submaximal intensity exercise under a ketogenic diet than are female athletes.

TRIAL REGISTRATION

Clinical Trials Gov, NCT03665948 . Registered 11 September 2018 (retrospectively registered).

From Paper to Podium: Quantifying the Translational Potential of Performance Nutrition Research

Sport nutrition is one of the fastest growing and evolving disciplines of sport and exercise science, demonstrated by a 4-fold increase in the number of research papers between 2012 and 2018. Indeed, the scope of contemporary nutrition-related research could range from discovery of novel nutrient-sensitive cell-signalling pathways to the assessment of the effects of sports drinks on exercise performance. For the sport nutrition practitioner, the goal is to translate innovations in research to develop and administer practical interventions that contribute to the delivery of winning performances. Accordingly, step one in the translation of research to practice should always be a well-structured critique of the translational potential of the existing scientific evidence. To this end, we present an operational framework (the "Paper-2-Podium Matrix") that provides a checklist of criteria for which to prompt the critical evaluation of performance nutrition-related research papers. In considering the (1) research context, (2) participant characteristics, (3) research design, (4) dietary and exercise controls, (5) validity and reliability of exercise performance tests, (6) data analytics, (7) feasibility of application, (8) risk/reward and (9) timing of the intervention, we aimed to provide a time-efficient framework to aid practitioners in their scientific appraisal of research. Ultimately, it is the combination of boldness of reform (i.e. innovations in research) and quality of execution (i.e. ease of administration of practical solutions) that is most likely to deliver the transition from paper to podium.

Ketone body supplement label claims: what supplement has been supplemented?

Background

There is a keen interest in performance-enhancing supplementation and the associated benefits, despite reports of incorrect label claims made by manufacturers and the questionable efficacy of the supplements. The use of ketone body supplements as a source of fuel during exercise and sporting performance, in particular, is of interest to sportspeople. By increasing blood ketone body levels, with an accompanying decrease in blood glucose, may indicate a state of nutritional ketosis, whereby the body no longer relies on glucose metabolism but rather the metabolism of ketone bodies. This could be beneficial for long, slow steady-state endurance exercise.

Discussion

There are numerous ketone body supplements on the market manufactured in South Africa and internationally. However, unlike medicines, the sports supplementation industry is poorly regulated. Furthermore, ketone body supplementation with regard to its effects on improving exercise and athletic performance is still unconvincing.

Conclusion

Within the ever-changing sports supplementation industry, ketone body supplements are being used despite controversies regarding the accuracy and scientific merit of label claims. The ingredients and their quantities, as well as the performance benefits, need to be objectively validated.

Identification of a select metabolite panel for measuring metabolic perturbation in response to heavy exertion

INTRODUCTION AND OBJECTIVE

Databases from three global metabolomics-based studies (N = 59) (PMID: 25409020, 26561314, 29566095) were evaluated for metabolite shifts following heavy exertion (75-km cycling) to generate a representative, select panel of metabolites identified by variable importance in projection (VIP) scores.

METHODS AND RESULTS

OPLS-DA was used to separate samples at pre- and post-exercise during the water-only trial in one of the studies (PMID: 26561314), and of 590 metabolites, 26 (all but one from the lipid pathway) had a VIP > 2 and were selected for the panel. A second OPLS-DA based on the 26 metabolites was performed to separate pre- and post-exercise samples, and this model performed as well as the one with 590 metabolites (Q2Y = 0.923, 0.925 respectively); this model also showed a complete separation using OPLS-DA plots between pre- and post-exercise samples for the other two studies. A latent variable t1 (a linear combination of the 26 metabolites), was generated and the metabolite data at each time point were projected to t1 with the relative distance on t1 and area under the curve (AUC) determined from the three databases. Acute carbohydrate compared to water-only ingestion was linked to a 28-47% reduction in AUCs following exercise depending on the carbohydrate source and recovery time period.

CONCLUSIONS

These data support that a panel of 26 metabolites can be used to represent global metabolite increases induced by prolonged, intensive exercise. This select panel includes metabolites primarily from the lipid super pathway, and exercise-induced increases are sensitive to the moderating effect of acute carbohydrate ingestion.

The effects of beetroot juice supplementation on exercise economy, rating of perceived exertion and running mechanics in elite distance runners: A double-blinded, randomized study

Purpose

Nitrate-rich beetroot juice supplementation has been extensively used to increase exercise economy in different populations. However, its use in elite distance runners, and its potential effects on biomechanical aspects of running have not been properly investigated. This study aims to analyze the potential effects of 15 days of beetroot juice supplementation on physiological, psychological and biomechanical variables in elite runners.

Methods

Twelve elite middle and long-distance runners (age = 26.3 ± 5.1yrs, VO₂Max = 71.8±5.2 ml*kg^-1*min^-1) completed an incremental running test to exhaustion on a treadmill before and after a 15-days supplementation period, in which half of the group (EG) consumed a daily nitrate-rich beetroot juice and the other group (PG) consumed a placebo drink. Time to exhaustion (TEx), running economy, vastus lateralis oxygen saturation (SmO₂), leg stiffness and rate of perceived exertion (RPE) were measured at 15, 17.1 and 20 km/h during the incremental test.

Results

Likely to very likely improvements in EG were observed for the RPE (Standardized mean difference (SMD) = -2.17, 90%CI = -3.23, -1.1), SmO₂ (SMD = 0.72, 90%CI = 0.03, 1.41) and TEx (SMD = 1.18, 90%CI = -0.14, 2.5) in comparison with PG. No other physiological or biomechanical variable showed substantial improvements after the supplementation period.

Conclusions

Fifteen days of nitrate-rich beetroot juice supplementation produced substantial improvements in the time to exhaustion in elite runners; however, it didn’t produce meaningful improvements in running economy, VO₂Max or mechanical parameters.

Ketone bodies as epigenetic modifiers

PURPOSE OF REVIEW

Ketone body metabolism is a dynamic and integrated metabolic node in human physiology, whose roles include but extend beyond alternative fuel provision during carbohydrate restriction. Here we discuss the most recent observations suggesting that ketosis coordinates cellular function via epigenomic regulation.

RECENT FINDINGS

Ketosis has been linked to covalent modifications, including lysine acetylation, methylation, and hydroxybutyrylation, to key histones that serve as dynamic regulators of chromatin architecture and gene transcription. Although it remains to be fully established whether these changes to the epigenome are attributable to ketone bodies themselves or other aspects of ketotic states, the regulated genes mediate classical responses to carbohydrate restriction.

SUMMARY

Direct regulation of gene expression may occur in-vivo via through ketone body-mediated histone modifications during adherence to low-carbohydrate diets, fasting ketosis, exogenous ketone body therapy, and diabetic ketoacidosis. Additional convergent functional genomics, metabolomics, and proteomics studies are required in both animal models and in humans to identify the molecular mechanisms through which ketosis regulates nuclear signaling events in a myriad of conditions relevant to disease, and the contexts in which the benefits of ketosis might outweigh the risks.

Metabolic and molecular framework for the enhancement of endurance by intermittent food deprivation

Evolutionary considerations suggest that the body has been optimized to perform at a high level in the food-deprived state when fatty acids and their ketone metabolites are a major fuel source for muscle cells. Because controlled food deprivation in laboratory animals and intermittent energy restriction in humans is a potent physiologic stimulus for ketosis, we designed a study to determine the impact of intermittent food deprivation during endurance training on performance and to elucidate the underlying cellular and molecular mechanisms. Male mice were randomly assigned to either ad libitum feeding or alternate-day food deprivation (ADF) groups, and half of the mice in each diet group were trained daily on a treadmill for 1 mo. A run to exhaustion endurance test performed at the end of the training period revealed superior performance in the mice maintained on ADF during training compared to mice fed ad libitum during training. Maximal O₂ consumption was increased similarly by treadmill training in mice on ADF or ad libitum diets, whereas respiratory exchange ratio was reduced in ADF mice on food-deprivation days and during running. Analyses of gene expression in liver and soleus tissues, and metabolomics analysis of blood suggest that the metabolic switch invoked by ADF and potentiated by exercise strongly modulates molecular pathways involved in mitochondrial biogenesis, metabolism, and cellular plasticity. Our findings demonstrate that ADF engages metabolic and cellular signaling pathways that result in increased metabolic efficiency and endurance capacity.-Marosi, K., Moehl, K., Navas-Enamorado, I., Mitchell, S. J., Zhang, Y., Lehrmann, E., Aon, M. A., Cortassa, S., Becker, K. G., Mattson, M. P. Metabolic and molecular framework for the enhancement of endurance by intermittent food deprivation.

Effect of acute ingestion of β-hydroxybutyrate salts on the response to graded exercise in trained cyclists

Acute ingestion of ketone salts induces nutritional ketosis by elevating β-hydroxybutyrate (βHB), but few studies have examined the metabolic effects of ingestion prior to exercise. Nineteen trained cyclists (12 male, 7 female) undertook graded exercise (8 min each at ∼30%, 40%, 50%, 60%, 70%, and 80% VO_2peak) on a cycle ergometer on two occasions separated by either 7 or 14 days. Trials included ingestion of boluses of either (i) plain water (3.8 mL kg body mass^-1) (CON) or (ii) βHB salts (0.38 g kg body mass^-1) in plain water (3.8 mL kg body mass^-1) (KET), at both 60 min and 15 min prior to exercise. During KET, plasma [βHB] increased to 0.33 ± 0.16 mM prior to exercise and 0.44 ± 0.15 mM at the end of exercise (both p < .05). Plasma glucose was 0.44 ± 0.27 mM lower (p < .01) 30 min after ingestion of KET and remained ∼0.2 mM lower throughout exercise compared to CON (p < .001). Respiratory exchange ratio (RER) was higher during KET compared to CON (p < .001) and 0.03-0.04 higher from 30%VO_2peak to 60%VO_2peak (all p < .05). No differences in plasma lactate, rate of perceived exertion, or gross or delta efficiency were observed between trials. Gastrointestinal symptoms were reported in 13 out of 19 participants during KET. Acute ingestion of βHB salts induces nutritional ketosis and alters the metabolic response to exercise in trained cyclists. Elevated RER during KET may be indicative of increased ketone body oxidation during exercise, but at the plasma βHB concentrations achieved, ingestion of βHB salts does not affect lactate appearance, perceived exertion, or muscular efficiency.