https://orcid.org/0000-0002-3693-250X
Abstract
The impact of a ketogenic diet (KD) (<50 g/d carbohydrate, >75% fat) on athletic performance has sparked much interest and self-experimentation in the past 3–4 years. Evidence shows 3–4-week adaptations to a KD in endurance-trained athletes were associated with maintenance of moderate (46–63% VO2max) and vigorous intensity (64–90% VO2max) endurance exercise, while at intensities >70% VO2max, increases in fat oxidation were associated with decreased economy (increased oxygen consumption), and in some cases, increased ratings of perceived exertion and heart rate. Two investigations in recreationally active endurance athletes noted no vigorous intensity exercise decrement following 3- and 12-week adaptations. Moderate (70–85% one repetition maximum) and near-maximal to maximal intensity (>85% 1RM) strength performance experienced no decrement following a 3-12-week KD adaptation. Beneficial effects were noted for 2000 m sprint and critical power test completed for short duration at vigorous intensity, while two additional tests noted no decrement. For sprint, near-maximal exercise (>91% VO2max), benefit of the KD was observed for six-second sprint, while no decrement in performance was noted for two additional maximal tests. When protein is equated (grams per kilogram), one investigation noted no decrement in muscle hypertrophy, while one noted a decrement. One investigation with matched protein noted the KD group lost more body fat. In conclusion, moderate-to-vigorous intensity exercise experiences no decrement following adaptation to a KD. Decreases in exercise economy are observed >70% VO2max in trained endurance athletes which may negate performance within field settings. Beneficial effects of the KD during short duration vigorous, and sprint bouts of exercises are often confounded by greater weight loss in the KD group. With more athletes pursuing carbohydrate-restricted diets (moderate and strict (KD)) for their proposed health benefits, more work is needed in the area to address both performance and health outcomes.
Introduction
Exercise lasting more than a couple of minutes in duration is fueled by a combination of intra-muscular and extra-muscular carbohydrates, and lipids, with minor contribution from amino acids.Citation1 Since the introduction of muscle biopsy technique for determination of human muscle metabolism in the 1960s, it has been widely accepted that possessing high-levels of pre-exercise muscle glycogen is a precursor for optimal athletic performance.Citation2 Sports nutrition guidelines have reflected this, recommending carbohydrate-based diets,Citation3 and more recently, periodized carbohydrate-based diets,Citation4 to optimize athletic performance for an array of sports and physical endeavors.
Interest in low-carbohydrate alternatives grew following publications by Phinney and colleagues in the 1980s, demonstrating, overweight patientsCitation5 and well-trained cyclistsCitation6 could sustain exercise capacity at submaximal intensities following 21–28 days of a low-carbohydrate ketogenic diet (KD), respectively. A KD is characterized by low-carbohydrate (<20–50 g/d), moderate protein and high-fat (>75–80% energy) intakes,Citation7,Citation8 with prioritization of monounsaturated and saturated fatty acids recommendedCitation7 and observed within the literature.Citation9 Following preliminary KD work,Citation5,Citation6 through the years 1995–2005, extensive work examined acute (<5 days) low-carbohydrate, high-fat (LCHF) diets (~25% carbohydrate energy, >60% fat energy). This work attempted to increase fat oxidation during submaximal exercise, i.e., slow the oxidation of finite carbohydrate stores, and sustain near-maximal performance through increased carbohydrate availability, stemming from less oxidation at submaximal intensities. Despite increased fat oxidation, and maintenance of glycogen stores, no clear performance benefits were noted.Citation10
More recently, a KD has (re)grownCitation11 in popularity, following popular publication in lay press,Citation7 and within peer-reviewed literature.Citation10,Citation12 Similar to an LCHF diet, a KD is associated with an elevation in circulating free fatty acids. Due to relative glucose deprivation attributing from greater carbohydrate restriction, a KD is associated with an elevation in ketone bodies, namely, acetone, acetoacetate (AcAc) and beta-hydroxybutyrate (βHB).Citation8 βHB is the primary ketone body found in peripheral tissues, and in circulation, therefore, it is a common measure of ketogenesis and dietary adherence.Citation8 Its elevation represents the balance between hepatic production and peripheral breakdown, with values of 0.5–3.0 mM βHB demonstrating “nutritional ketosis”.Citation7,Citation8 During nutritional ketosis, ketones bodies replace glucose as the primary fuel source for peripheral tissues, such as the brain and heart.Citation8
Whether nutritional ketosis yields any tangible performance benefits to athletes is a contentious subject within nutrition science.Citation10,Citation12 This academic debate has brought about several investigations in an array of athletes, including endurance athletes, resistance-trained athletes, and CrossFit trainees. The aim of this review is to examine the KD performance literature to determine if performance benefits exist for athletes and recreationally trained athletes, and to provide some clinical insights as to the place of LCHF and KDs in athletes.
Materials And Methods
Literature Search
Keyword searches took place on electronic databases including PubMed and SPORTDiscus. Search terms included “performance”, AND “ketogenic”, AND “keto”, AND “keto-adapted”, AND “carbohydrate”, AND “fat”, AND “low-carbohydrate”, AND “high-fat”, AND “low-fat”, AND “high-carbohydrate”, AND “body composition”, AND, “hypertrophy”, AND “fat loss”, AND “weight loss”, AND “endurance athlete”, AND “resistance training”, AND “powerlifting”, AND ”Olympic weightlifting“, AND “athlete”. Search terms were entered in several combinations. Manual searches were conducted using reference lists of existing narrative, and meta-analytic reviews on LCHF/KD performance literature.
Study Selection
Study selection criteria were as follows: 1) a controlled KD trial, defined by a) dietary analysis indicating <50 g/d carbohydrate and/or b) ketone bodies (>0.5 ± 0.1 mM βHB);Citation7,Citation8 2) within a trained or recreationally trained athlete population, 3) measured cardiorespiratory or musculoskeletal physical fitness,Citation13 a) cardiorespiratory fitness at moderate intensity (46–63% maximal oxygen consumption (VO2max)), b) cardiorespiratory fitness at vigorous intensity (64–90% VO2max), c) short duration (>30 s, <60 mins) vigorous exercise (64–90% VO2max), d) sprint-near maximal exercise (<30 s) (~91% VO2max), e) strength at moderate (50–69% one repetition maximum (1RM)) to vigorous intensity (70–84% 1RM), f) strength at maximal intensity (>85% 1RM), or g) body composition with matched protein intakes (% energy, or g⋅kg).
Participant Classification
To improve the translational quality of this work, and because differences in ketone metabolism are reported between trained and untrained persons,Citation8 groups will be classified according to training status.Citation14
Cardiorespiratory Fitness
Participants were categorized as, a) trained athletes and b) recreationally trained athletes, according to how original manuscripts defined training status. Classification according to traditional standards (VO2max, peak power output, etc.)Citation14 is not possible, as many investigations either failed to appropriately assess VO2max or peak power output, or, contained males and females, and gender-specific values were not described.
Strength And Body Composition
Investigations containing participants for strength and body composition assessment were categorized as (a) trained and (b) recreationally trained, due to varying dose responses observed by both populations.Citation15
Exclusion Criteria
Study exclusion criteria were as follows: 1) implementation of a KD, but report a carbohydrate intake >50 g/d, 2) case study, or 3) cross-sectional study, 4) recreationally active endurance athletes with VO2max <50.0 mL⋅kg⋅min−1, and 5) participants >50 years of age.
Results
Thirteen investigations met the inclusion criteria and are presented in – as follows: : Endurance; : Strength; : Short duration and : Body composition.
Table 1 Endurance Capacity In Athletes Consuming A Ketogenic Diet At A Variety Of Intensities
Table 2 Strength Performance In Athletes Consuming a Ketogenic Diet At A Variety Of Intensities
Table 3 Short-Duration Exercise In Athletes Consuming a Ketogenic Diet At A Variety Of Intensities
Table 4 Body Composition In Athletes Consuming a Ketogenic And Non-Ketogenic Diet With Matched Protein Intakes
Endurance Performance
Moderate Intensity (46–63% VO2max)
Endurance-trained athletes experienced no decrement in endurance capacity following 28-day adaptation to a KD ().Citation6
Vigorous Intensity (64–90% VO2max)
Endurance-trained athletes adhered to a KD for 21–31 days, and maintained time to exhaustion (TTE) at 70% VO2max, and 10 km TT performance ().Citation16,Citation17 Recreationally trained endurance athletes experienced no decrement to endurance performance following 21–84 day KD adherence ().Citation18,Citation19
Strength Performance
Moderate (50–69% 1RM) To Vigorous Intensity (70–84% 1RM)
No decrement in strength endurance and power, and isometric strength were observed following 3–4 weeks of a KD in trained gymnasts and taekwondo athletes ().Citation20,Citation21
Near-Maximal To Maximal Intensity (>85% 1RM)
Resistance training coupled with a KD for 10–12 weeks maintained 1RM back squat, bench press, clean, jerk, and deadlift performance within trained athletes ().Citation22,Citation23 Recreational athletes experienced no decrement in 1RM back squat, bench press and max press-ups ().Citation24
Short-Duration Performance
Vigorous Intensity (64–90% VO2max, >30 s)
Beneficial effects for 2000 m run performance were noted following 21-day adaptation within trained taekwondo athletes ().Citation20 No decrement to 400 m outdoor run, graded exercise test TTE and 5 x 3 min interval sprints were observed within recreationally trained athletes ().Citation19,Citation24–Citation26 Beneficial effects for completion of CPT were observed following 12-week adherence within recreational endurance athletes ().Citation19
Sprint-Near Maximal Exercise (>91% VO2max, <30 s)
Wingate and 100 m sprint performance experienced no decrement following 21-day adaptation within trained athletes ().Citation21 Six second (SS) sprint performance improved,Citation19 and 30–15 sprint performance experienced no decrement following 12-week KD adherence within recreationally trained athletes ().Citation26
Body Composition
Knowledge relating to the KD and muscle hypertrophy is mixed; an investigation within trained athletes noted no decrement (),Citation22 while an investigation within recreationally trained athletes noted a decrement ().Citation27 Body fatness remained unchanged within trained athletes (), while recreationally trained athletes consuming a KD experienced decreases in body fat ().
Discussion
Endurance – Moderate Intensity (46–63% VO2max)
Trained Athletes
Phinney demonstrated that 28 days of a KD was a sufficient duration to retool the muscle mitochondria to sustain endurance capacity at moderate intensity ().Citation6 One of the arguments put forward for endurance athletes to consume a KD is humans’ limited stores of carbohydrate (~2200 kcal) versus fat (~30,000 kcal in someone with 7–14% body fat).Citation12 It was hypothesized that athletes would have a greater capacity to complete moderate-intensity exercise, relying on a combination of free fatty acids, ketone bodies, muscle and hepatic glycogen, and increased glucose from fat- and protein-derived precursors (gluconeogenesis), when keto-adapted.Citation7,Citation12 Despite achieving nutritional ketosis and increased lipid oxidation, endurance capacity remained limited by glucose availability ().Citation6 Prior to the commencement of exercise, glycogen stores were reduced by ~45% (76 vs 140 mM/kg wet weight muscle) following a KD. Webster et alCitation28 noted endurance-trained athletes consuming a KD for >8 months oxidized 1.21 ± 0.15 g⋅min−1 of carbohydrate, versus 2.89 ± 0.41 g⋅min−1 in a homogenous group consuming a mixed diet (49% carbohydrate, 33% fat), and produced similar glucose through gluconeogenesis at 72% VO2peak. Therefore, similar to a carbohydrate-based athlete, carbohydrate feeding appears necessary when keto-adapted to sustain moderate-intensity exercise >3 hrs, at a rate of >1–2 g⋅min−1,Citation28 if findings were to be replicated within experimental settings.
Endurance – Vigorous Intensity (64–90% VO2max)
Trained Athletes
Decreased economy observed at vigorous intensity is noteworthy as it better represents the intensity of competitive endurance athletes ().Citation16,Citation17 For example, “fast runners” complete a treadmill-based marathon in 2 hrs 43 mins at 75% VO2max, while “slower runners” complete 3 hrs 20 min marathon at 65% VO2max.Citation29 Increased oxygen cost of ATP production from fatty acids versus carbohydrate has been understood since the early 1900s.Citation30 Unfortunately, due to the nature of field tests, extensive blood and gas analysis did not take place during the 10 km TT; therefore, it is difficult to precisely determine the KD's limiting factor.Citation16 However, considering increased oxygen consumption, and that HR and RPE were evident at 20 km race pace within laboratory settings, decreased efficiency was likely a contributing factor at 10 km race pace,Citation16 or perhaps, it could be argued the adaptation period was too brief. The length of an adaptation period is often identified as important when discussing a KD and an athlete’s ability to regain performance, with advocates suggesting months necessary to become keto-adapted.Citation7,Citation12,Citation31,Citation32 Questionably, however, race walkers achieved higher rates of fat oxidation (1.54 ± 0.18 g⋅min−1 at 70% VO2maxCitation32 vs 1.57 ± 0.32 g⋅min−1 at 80% VO2peakCitation16) during a 25 km walk, and similar concentrations of βHB (both, >0.5–1.0 mM) to a group habituated to a KD for >9 months,Citation32 in as little as 21 days.Citation16 Therefore, it remains unclear, what other measurable adaptations, if any, must take place prior to an athlete being considered keto-adapted.
Recreationally Trained Athletes
Endurance performance ranging from 70 to 168 mins in duration was sustained in recreationally trained individuals ().Citation18,Citation19 Heatherly and colleagues suggested a KD affords an opportunity “to eat to satiety while maintaining a more competitive racing weight and body composition versus high carbohydrate (HC)” (pg. 578).Citation18 It is noteworthy that participants lost weight (−2.5 kg, p<0.001) whilst being instructed to eat fat ad libitum, but it is important to note that body composition improvements can be achieved with low- or high-carbohydrate intakes, granted protein and caloric needs are appropriate.Citation33 From work in trained individuals,Citation16,Citation17 adopting a KD to improve running economy could be counterproductive, or at least negligible, if metabolic efficiency is negated >70% VO2max,Citation16,Citation17 versus ensuring carbohydrate availability and implementing an energy deficit. Improved economy attributing from weight loss was not a confounding variable within McSwiney et al due to 100 km TT being completed on a stationary bike (WattBike) with self-selected resistance.Citation19 Notably, 100 km TT performance was sustained, despite the KD group consuming only water and electrolytes during post-intervention testing, versus the HC group who consumed 30–60 g/h of carbohydrate.Citation19 Whether performance can be sustained >100 km without carbohydrate feeding within recreationally trained athletes remains to be seen within experimental settings. However, experimental and non-experimental work in trained endurance athletes would suggest carbohydrate feeding is necessary to sustain moderate to vigorous activity >3 hrs.Citation6,Citation28
Strength Performance
Moderate (50–69% 1RM) To Vigorous Intensity (70–84% 1RM)
Despite <50 g/d of carbohydrates, trained gymnasts and taekwondo athletes experienced no decrement in strength endurance and power following 3–4-week adherence ().Citation20,Citation21 Maintenance of performance in both KD diet groups achieved significant weight loss is noteworthy, as a lean physique and making weight while limiting negative impacts on performance are important to each respective sport.Citation20,Citation21 Notably however, there were considerable discrepancies in protein intakes within Paoli et al (HC 1.1 g⋅kg protein, KD 3.1 g⋅kg protein)Citation20 and Rhyu and Cho (HC 30% protein, KD 40.5% protein)Citation21 investigations, which likely contributed to ad libitum weight loss,Citation20 with the KD group outperforming the control group in terms of weight loss,Citation21 through improved satiety and other mechanisms.Citation33
Near-Maximal To Maximal Intensity (>85% 1RM)
Until recently, maximal strength performance through 1RM in response to a KD remained unexplored. Current evidence suggests no decrement in maximal strength (). A 1RM represents an extreme of the exercise continuum, requiring maximal-force production. Short-duration, maximal-force production is fuelled primarily by ATP within the muscle, and the ATP phosphagen system.Citation1 Rest, or recovery periods allow replenishment of oxygen stores, and resynthesis of ATP and phosphocreatine within muscle.Citation1 Therefore, granted a 1RM is performed in a rested state, which is currently the case within the literature, strength performance will likely experience no decrement through KD consumption.
Short-Duration Vigorous Intensity (64–90% VO2max, >30 s)
Evidence suggests no decrement to short-duration vigorous-intensity exercise following 3–12 weeks of a KD within trained ()Citation21 and recreationally trained athletes ().Citation19,Citation24–Citation26 Findings are contrary to sports nutrition guidelines, which recommend carbohydrate availability to enable vigorous performance.Citation3,Citation4 However, improved 2000 m performance (duration: >8 mins),Citation21 and maintenance of CPT (duration: 3 mins)Citation19 can be explained mechanistically. For example, world-class, female cyclists completing a 3000 m pursuit (duration: 3:30 mins), and males completing 4000 m pursuit (duration: 4:11 mins) rely on ~75%, and ~85% aerobic metabolism, respectively.Citation34 Therefore, although not a measured component, aerobic metabolism likely fuelled a large proportion of the 3–8 min tests. As previously noted (–), a KD is proficient at sustaining aerobic performance. Maintenance of 400 m sprint performance is noteworthy, however,Citation24 considering 400 m sprints are glycolytic.Citation35 Findings were confounded by weight loss (KD −3 kg p=0.022; CTL −0.3 kg p>0.05),Citation24 which would improve running economy (power-to-weight ratio),Citation36 and potentially mask metabolic inefficiency observed >70% VO2max.Citation16,Citation17
Collectively, available literature suggest graded exercise test performance ranging from 19.8 to 27.2 mins in duration is sustained following 4–12-week adaption.Citation25,Citation26 Using muscle biopsies, a 4-fold reduction in muscle glycogen was observed following a 28-day KD,Citation6 while cross-sectional studies have observed a 1.8-fold reduction,Citation28 and no decrement,Citation32 following >8,Citation28 and >9 monthsCitation32 adherence. If this is a stepwise occurrence, it is suggestive that greater resting muscle glycogen stores are achieved following elongated adaptation, despite reported, continued <50 g/d carbohydrate intake.Citation28,Citation32 If true, and whether longer adaptations, for example, 9 months,Citation32 enables improved performance of vigorous-intensity exercise through the greater reestablishment of resting glycogen stores remains to be seen within experimental settings.
Sprint-Near Maximal Intensity (>90% VO2max, <30 s)
No decrement to Wingate,Citation21 100 m sprintCitation21 and 30–15 repeated sprint performanceCitation23 were observed following 3–12-week adaptation, while benefit to SS sprint performanceCitation16 was observed following 12-week adherence within trained ()Citation21 and recreationally trained athletes ().Citation16,Citation23 The phosphocreatine energy system would likely fuel SS sprint,Citation1 while during a Wingate, healthy subjects utilize 16% aerobic, 56% glycolytic, and 28% phosphocreatine energy systems.Citation37 Although maintenance of sprint-near maximal intensity exercise with reduced carbohydrate intake is noteworthy, it is important to consider findings in context. For example, tests were performed in taekwondo athletes attempting to make weight, where fatigue and reduced glycogen stores were likely a contributing factor,Citation21 and within recreationally trained endurance athletes.Citation16,Citation23 Therefore, findings are not representational of well trained, or elite athletes who compete in events <30 s in duration, such as 100 and 200 m sprinters, with high anaerobic thresholds and carbohydrate availability.
Body Composition
For the first 10 weeks of Wilson et al’s investigation,Citation22 groups experienced similar muscle hypertrophy (). Thereafter, following 1 week of increased carbohydrate consumption (263.5 ± 42.0 g), the KD group increased body mass and estimations of lean body mass by ~3 kg,Citation22 bringing lean body mass across the 11-week intervention to 2.7 kg in the non-KD group, and 4.5 kg in the KD group (p>0.05).Citation22 This acute gain in lean body mass in week 11 is not entirely uncommon, considering 3 days of HC feeding and rest is associated with increased body mass (0.6 kg, p=0.001) and estimations of lean body mass (0.9 kg, p<0.0001) within non-obese men using a DXA scanner.Citation38
In contrast, Vargas et al demonstrated recreationally trained men consuming a non-KD increased lean body mass to a greater extent when compared to a KD group following an 8-week training intervention.Citation27 Baseline dietary assessment was absent, therefore, it is unknown if the non-KD group increased or sustained carbohydrate intake, thereby potentially impacting DXA reliability, for reasons previously outlined.Citation38 In addition, groups were instructed to consume a hyper-caloric diet to promote greater gains in lean body mass, however, mean body weight decreased within the KD group (−1.4 kg, TxG, p=0.016). Therefore, an appropriate synopsis is, a hypocaloric KD decreased fat mass, and maintained lean body mass (). Had carbohydrate restoration/loading taken place, to standardize habitual carbohydrate-availability (g⋅kg unknown from manuscript), increases in lean body mass parallel to the non-KD group, may have taken place, as previously observed.Citation22
Conclusions, Clinical Insights And Future Directions
Available knowledge demonstrates no clear performance benefit to athletes following a KD, with some benefit shown mainly in short duration, vigorous-intensity tests, when weight loss was likely a confounding variable. While many of the trials provided no performance benefit, it is important to note that a KD often did not cause a performance decrement, particularly in recreationally trained athletes. Decreases in metabolic efficiency were common among trained athletes competing at >70% VO2max following acute adaptation.Citation16,Citation17
Despite inconsistent outcomes, we continue to see in practice (i.e., anecdotally), endurance athletes pursuing a carbohydrate-restricted dietary approach. Long-term anecdotal and subjective evidence is mixed, however. For example, “elite ultra-marathoners and ironman distance triathletes”,Citation32 and ‘well-trained cyclists’Citation28 habituated towards a KD style of eating for 20Citation32 and 8 months,Citation28 respectively, report remaining highly competitive. Whilst a “world-class vegetarian long-distance triathlete”, reported their worst-ever half-Ironman performance (21 weeks), second-worst Ironman performance (24 weeks), and failed to complete Ironman in week 32, discontinuing the diet thereafter.Citation39
Maunder et al proposed that endurance athletes should adopt an exercise training session and nutritional practices to minimize the endogenous carbohydrate cost of exercise at competitive intensities, through adaptation to an LCHF or KD, whilst maximising pre-competition glycogen stores (carbohydrate feeding/restoration) and providing exogenous carbohydrate during competition.Citation40 As previously outlined, considerable research has identified that an acute LCHF diet (5–10 days) approach with carbohydrate restoration (6.8–11 g⋅kg CHO for 1–3 days) does not decrement endurance performance.Citation10 Conversely, there is strong evidence demonstrating that such an approach is associated with a reduction in glycogenolysis during exercise, and a reduction in the active form of pyruvate dehydrogenase at rest, and during submaximal and maximal exercise.Citation41 Whether these undesirable adaptations persist with longer adaptation periods remains to be seen mechanistically within experimental settings.
Furthermore, it was proposed that ketone bodies would provide fuel for the brain, in combination with greater contribution from gluconeogenic substrates.Citation7,Citation12 As previously outlined, Webster et al, provided evidence that the energy contribution from gluconeogenesis is not enhanced subsequent to 8 months of consuming a KD.Citation28 Therefore, non-experimentalCitation28 and experimental evidenceCitation6 suggest endurance performance remains limited through glucose availability in trained endurance athletes consuming a KD. Thus, the case for advocating a KD versus a less extreme LCHF diet must be questioned. Although this has not been specifically explored, if glycogen restoration and/or exogenous carbohydrate feeding were to take place during exercise, as is recommended,Citation39,Citation40 ketogenesis, hypothetically, would no longer take place due to increased glucose availability.Citation8 Therefore, it must be questioned why a KD is recommended, versus a less extreme LCHF diet, to achieve increases in fat oxidation, as ketone bodies’ contribution to energy expenditure would be negligible, if not obsolete, with current recommendations.Citation39,Citation40
A further reason why we propose the popularity of carbohydrate-restricted approaches is due to other reported benefits of this dietary approach. These include, reports of improved energy for both training and competition,Citation12 reductions in exogenous caloric requirements during training and competition,Citation12 improved symptoms derived from inflammatory conditions,Citation12,Citation42 and the reduced incidence of delayed onset of muscle soreness and gastrointestinal complaints.Citation12 Furthermore, nutritional ketosis has emerged as a potent modulator of inflammation over the past decade.Citation43,Citation44 Such a collection of outcomes may impact athletes’ overall health which could have potential downstream effect on performance; however, this is yet to be examined comprehensively in athletes within experimental settings. Therefore, heed must be taken, as many potential confounding variables may have been overlooked within anecdotal reports.
Future research on carbohydrate-restriction in athletes could also address aspects of health alongside performance – both quantitively and qualitatively. This will help connect the evidence with the growing interest and practice and provide further understanding of the potential, holistic benefits of carbohydrate-restriction in the athlete context.
Disclosure
The corresponding author, Dr Caryn Zinn has co-authored a book titled “What The Fat – Sports performance” which assume an LCHF nutrition approach; co-author, Dr Dan Plews, delivers an online course which focuses on LCHF nutrition for endurance athletes. The authors report no other conflicts of interest in this work.
References
- Egan B, Zierath JR. Exercise metabolism and the molecular regulation of skeletal muscle adaptation. Cell Metab. 2013;17(2):162–184. doi:10.1016/j.cmet.2012.12.01223395166
- Bergström J, Hultman E. A study of the glycogen metabolism during exercise in man. Scand J Clin Lab Invest. 1967;19(3):218–228. doi:10.3109/003655167090906296048626
- Burke LM, Hawley J, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29(1):17–27. doi:10.1080/02640414.2011.585473
- Jeukendrup AE. Periodized nutrition for athletes. Sports Med. 2017;47(Suppl 1):51–63. doi:10.1007/s40279-017-0694-228332115
- Phinney S, Horton E, Sims E. Capacity for moderate exercise in obese subjects after adaptation to a hypocaloric, ketogenic diet. J Clin Invest. 1980;66(5):1152–1161. doi:10.1172/JCI1099457000826
- Phinney S, Bistrian B, Evans W, Gervino E. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism. 1983;32(8):769–776. doi:10.1016/0026-0495(83)90106-36865776
- Volek J, Phinney S (2012). The art and science of low carbohydrate performance. Beyond Obesity LLC. Available from: https://scholar.google.com/scholar?q=2012+art+and+science+of+low+carbohydrate+living+volek&btnG=&hl=en≈sdt=0%2C5 Accessed 109, 2019.
- Evans M, Cogan K, Egan B. Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation. J Physiol. 2016. doi:10.1113/JP273185
- McSwiney FT, Doyle L. Low-carbohydrate ketogenic diets in male endurance athletes demonstrate different micronutrient contents and changes in corpuscular haemoglobin over 12 weeks. Sports. 2019;7(9):1–14. doi:10.3390/sports7090201
- Burke LM. Re-examining high-fat diets for sports performance: did we call the ’Nail in the Coffin’ too soon? Sports Med. 2015;45(1):33–49. doi:10.1007/s40279-015-0393-9
- Burke L. Low carb high fat (LCHF) diets for athletes – third time lucky? J Sci Med Sport. 2017;20:S1. doi:10.1016/j.jsams.2017.09.369
- Volek J, Noakes T, Phinney S. Rethinking fat as a fuel for endurance exercise. Eur J Sport Sci. 2015;15(1):13–20. doi:10.1080/17461391.2014.95956425275931
- Garber CE, Blissmer B, Deschenes MR, et al. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc. 2011;43(7):1334–1359. doi:10.1249/MSS.0b013e318213fef21694556
- De Pauw K, Roelands B, Cheung S, de Gues B, Rietjens G, Meeusen R. Guidelines to classify subject groups in sport-science research. Int J Sports Physiol Perform. 2013;8:111–122. doi:10.1123/ijspp.2015-015323428482
- Peterson M, Rhea M, Alvar B. Applications of the dose-response for muscular strength development: a review of meta-analytic efficacy and reliability for designing training prescription. J Strength Cond Res. 2005;19(4):950–958. doi:10.1519/R-16874.116287373
- Burke L, Ross M, Garvican-Lewis L, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol. 2017;595(9):2785–2807. doi:10.1113/JP27323028012184
- Shaw DM, Merien F, Braakhuis A, Maunder E, Dulson DK. Effect of a ketogenic diet on submaximal exercise capacity and efficiency in runners. Med Sci Sports Exerc. 2019;51:2135–2146. doi:10.1249/MSS.000000000000200831033901
- Heatherly AJ, Killen LG, Smith AF, et al. Effects of ad libitum low carbohydrate high-fat dieting in middle-age male runners. Med Sci Sports Exerc. 2017. doi:10.1249/MSS.0000000000001477
- McSwiney FT, Wardrop B, Hyde PN, LaFountain RA, Volek JS, Doyle L. Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes. Metabolism. 2018;81:25–34. doi:10.1016/j.metabol.2017.10.01029108901
- Paoli A, Grimaldi K, D’Agostino D, et al. Ketogenic diet does not affect strength performance in elite artistic gymnasts. J Int Soc Sports Nutr. 2012;9:34. doi:10.1186/1550-2783-9-3422835211
- Rhyu H, Cho S. The effect of weight loss by ketogenic diet on the body composition, performance-related physical fitness factors and cytokines of Taekwondo athletes. J Exerc Rehabil. 2014;10(5):326–331. doi:10.12965/jer.14016025426472
- Wilson JM, Lowery RP, Roberts MD, et al. The effects of ketogenic dieting on body composition, strength, power, and hormonal profiles in resistance training males. J Strength Cond Res. 2017;1. doi:10.1519/JSC.000000000000193528005635
- Greene DA, Varley B, Hartwig T, Chapman P, Rigney M. A low carbohdyrate ketogenic diet reduces body weight without compromising performance in power lifting and Olympic weightlifting athletes. J Strength Cond Res. 2018;00(00):1–10. doi:10.1519/JSC.0000000000002904
- Kephart WC, Pledge CD, Roberson PA, et al. The three-month effects of a ketogenic diet on body composition, blood parameters, and performance metrics in crossfit trainees: a pilot study. Multidiscip Digital Publishing Inst. 2018;6(1):1-11.
- Cipryan L, Plews DJ, Ferretti A, Maffetone PB, Laursen PB. Effects of a 4-week very low-carbohydrate diet on high-intensity interval training responses. J Sports Sci Med. 2018;17:259–267.29769827
- Dostal T, Plews DJ, Hofmann P, Laursen PB, Cipryan L. Effects of a 12-week very-low carbohydrate high-fat diet on maximal aerobic capacity, high-intensity intermittent exercise, and cardiac autonomic regulation: non-randomized parallel-group study. Front Physiol. 2019;10. doi:10.3389/fphys.2019.00912
- Vargas S, Romance R, Petro JL, et al. Efficacy of ketogenic diet on body composition during resistance training in trained men: a randomized controlled trial. J Int Soc Sports Nutr. 2018;15(1):1–9. doi:10.1186/s12970-018-0236-929311763
- Webster CC, Noakes TD, Chacko SK, Swart J, Kohn TA, Smith JAH. Gluconeogenesis during endurance exercise in cyclists habituated to a long-term low carbohydrate high-fat diet. J Physiol. 2016;594(15):4389–4405. doi:10.1113/JP27193426918583
- O’Brien M, Viguie C, Mazzeo R, Brooks G. Carbohydrate dependance during marathon running. Med Sci Sports Exerc. 1992;25(9):1009–1017.
- Zuntz N, Schumburg W. Studien zu einer Physiologie desMarsches. Berlin: August Hirschwald; 1901.
- Phinney S. Ketogenic diets and physical performance. Nutr Metab. 2004;1(1):2. doi:10.1186/1743-7075-1-2
- Volek JS, Freidenreich DJ, Saenz C, et al. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 2016;65(3):100–110. doi:10.1016/j.metabol.2015.10.02826892521
- Aragon AA, Schoenfeld BJ, Wildman R, et al. International society of sports nutrition position stand: diets and body composition. J Int Soc Sports Nutr. 2017;14(1):16. doi:10.1186/s12970-017-0174-y28630601
- Jeukendrup AE, Craig NP, Hawley JA. The bioenergetics of world class cycling. J Sci Med Sport. 2000;3(4):414–433. doi:10.1016/S1440-2440(00)80008-011235007
- Tipton KD, Jeukendrup AE, Hespel P. Nutrition for the sprinter. J Sports Sci. 2007;25(SUPPL. 1):5–15. doi:10.1080/02640410701607205
- Foster C, Lucia A. Strategies to improve running economy. Sports Med. 2007;37(4–5):316–319. doi:10.1007/s40279-014-0246-y17465597
- Smith JC, Hill DW. Contribution of energy systems during a Wingate power test. Br J Sports Med. 1991;25(4):196–199. doi:10.1136/bjsm.25.4.1961839780
- Rouillier M-A, David-Riel S, Brazeau A-S, St-Pierre DH, Karelis AD. Effect of an acute high carbohydrate diet on body composition using DXA in young men. Ann Nutr Metab. 2015;66(4):233–236. doi:10.1159/00043584026183608
- Mujika I. Case study : long-term low-carbohydrate, high-fat diet impairs performance and subjective well-being in a world-class vegetarian long-distance triathlete. Int J Sport Nutr Exerc Metab. 2019;29(3):339–344. doi:10.1123/ijsnem.2018-012430160554
- Maunder E, Kilding AE, Plews DJ. Substrate metabolism during ironman triathlon: different horses on the same courses. Sports Med. 2018;1–8. doi:10.1007/s40279-018-0938-9
- Stellingwerff T, Spriet LL, Watt MJ, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol. 2006;290(2):380–388. doi:10.1152/ajpendo.00268.2005
- Zinn C, Wood M, Williden M, Chatterton S, Maunder E. Ketogenic diet benefits body composition and well-being but not performance in a pilot case study of New Zealand endurance athletes. J Int Soc Sports Nutr. 2017;14(22):1–9. doi:10.1186/s12970-017-0180-028096757
- Paoli A, Rubini A, Volek J, Grimaldi K. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013;67(8):789–796. doi:10.1038/ejcn.2013.11623801097
- Newman J, Verdin E. Ketone bodies as signaling metabolites John. National Inst Health. 2014;25(1):42–52. doi:10.1016/j.tem.2013.09.002