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The role of the ketogenic diet in exercise performance

Medicina Sportiva (2016), vol. XII, no 2, 2756-2761
Journal of the Romanian Sports Medicine Society
The role of the ketogenic diet in exercise performance
Evan E. Schick
Physiology of Exercise Sport (PEXS) Laboratory, California State University, Long Beach,
California, 90840
Abstract. Muscle glycogen storage and degradation are nearly universally accepted as crucial metabolic processes for
ensuring adequate intramuscular energy levels during prolonged, high-intensity activity. However, a growing body of
data illustrates that alternative substrates, such as ketone bodies, may be equally as effective in transducing energy
during exercise. Ketosis, wherein ketones serve as the primary oxidative fuel, can be achieved nutritionally through a
low-carbohydrate, high-fat ketogenic diet (KD). Though the KD is unequivocally successful in facilitating weight-loss
with minimal sacrifice to lean mass, current research indicates a complex role for the KD in both anaerobic and aerobic
exercise performance. This review discusses: 1) the mechanisms behind KD adaptation, and the effect of KD adaptation
on 2) glycogen metabolism, 3) aerobic exercise performance and 4) anaerobic exercise performance.
Key words: low-carbohydrate, high-fat, metabolism, athlete.
Use of a low-carbohydrate, high-fat ketogenic diet (KD) is widely recognized as an efficacious therapy for a
range of metabolic and neurodegenerative diseases and cancers (1-7). Clinical use of the KD has gained
popularity as its effects often mirror those reached pharmacologically yet are attained with little off-target
risk). However, interest in the KD extends beyond the clinical landscape as mounting evidence suggests that
the KD may also influence exercise performance and adaptation). Though its precise role within exercise
training and performance remains elusive, the notion that the KD might enhance exercise performance
remains contentious, as it challenges traditional, carbohydrate (CHO)-centric guidelines for exercise and
sport nutrition. Though past reviews have cohesively and comprehensively summarized ketone biochemistry
and its clinical role, this paper aims at unifying current findings most directly implicated in exercise
performance including: 1) the cellular mechanisms of KD adaptation as well as (2) the effects of KD on
glycogen metabolism, 3) aerobic exercise and 4) anaerobic exercise (8-12).
Due to its storage abundance, intracellular location and rapid energy provision, muscle glycogen has
long been held as the most important energy substrate during prolonged, high intensity exercise. This belief
has resulted in the decades-long practice of CHO loading prior to competition among endurance athletes
looking to achieve supra-maximal glycogen levels (13). The high fat and low CHO nutrient apportionment of
the KD conflicts with conventional, CHO-centered sports nutrition guidelines, which recommend up to 12
grams/kilogram body weight for those engaged in high intensity endurance programs (14). Depending on the
goal of the individual, the KD may be hypocaloric, eucaloric or hypercaloric and is typically comprised of a
3:1 to 4:1 energy ratio of fat to protein and CHO; though CHO restrictive diets with lower ratios of fat to
protein can also be ketogenic (2, 15).
The biochemical underpinning of the KD is hepatic synthesis of ketone bodies, Acetoacetate (AcAc)
and H-β-hydroxybutyrate (βHB). Hepatic ketogenesis, upregulated as a consequence of limited carbohydrate
supply and abundant fatty acid availability, converts acetyl CoA’s, generated at rates prohibiting tri-
carboxylic acid cycle entry, to AcAc and βHB (16). Both AcAc and βHB are transported via systemic
circulation to extrahepatic tissues, where they are oxidized as needed (16, 17). In healthy fed adult humans,
ketone oxidation represents only a minor fraction of total body energy expenditure, however, its contribution
to energy metabolism in the heart, brain and muscle significantly increases in many physiological and
pathological states including the neonatal period, fasting, starvation, repressed insulin production, insulin
resistance prolonged exercise and low-carbohydrate diets (2, 11, 12, 17-19).
The role of the ketogenic diet in exercise performance
Evan E. Schick
Medicina Sportiva
In fact, ketones -mainly βHB- supply up to 70% of the energy used by the brain during starvation with the
remainder provided by endogenously derived glucose (17). Traditionally, in the before mentioned conditions,
ketosis is seen as a metabolic means of holding serve until an adequate supply of blood glucose is available.
Mechanisms of KD Adaptation
Understanding the mechanisms by which the body responds to the considerable shifts in macronutrient
consumption and subsequent fuel utilization is crucial, as adaptation to a KD must be attained in order to
normalize or improve performance. Dietary fat, ingested in substantial quantities to induce a state of ketosis,
becomes the primary oxidative fuel by mass action. Subsequently, active tissues undergo a two-fold response
to accommodate elevated fatty acid flux: increased mitochondrial β-oxidation and reduced glucose oxidation.
Ample support for this tissue-level response has been provided, however, it is imperative to understand the
cellular mechanisms responsible for this metabolic shift. Heightened β-oxidation is accomplished through an
adaptive cellular response observed in studies of both animals and trained cyclists wherein prolonged KD
(>1 week) amplified the activity of skeletal muscle carnitine acyltransferase (CAT) and hydroxyacyl-
coenzyme A dehydrogenase (3-HAD) relative to the activity of citrate synthase (CS) (20-24). Analogous
gene expression data has revealed a pointed prioritization of fat oxidation over its storage as upregulation of
CD36, butyrate dehydrogenase (HBDH) and mitochondrial uncoupling protein-2 (UCP-2) was concomitant
to reduced expression of fatty acid synthase (FAS) in the livers of KD-adapted mice (25). Similar studies of
high-fat diet adaptation provide evidence of depressed glucose oxidation associated with reductions in
pyruvate dehydrogenase activity and both insulin and exercise stimulated muscle glucose transport (26, 27).
Provided that endurance training boosts capacity for fat oxidation, these tissue and cell-level adaptations
suggest that the KD might catalyze physiological responsiveness to an endurance exercise program (28).
KD Adaptation and Glycogen Utilization
Significant evidence links adaptation to the KD to altered muscle glycogen metabolism. Short term (3-14
days) KD has been reported to decrease baseline liver and muscle glycogen levels in rats and trained cyclists
(20, 29, 30). However, in a study of moderately obese subjects following six weeks of a KD, resting muscle
glycogen content was 57% of baseline after week 1 but increased to 69% of baseline values after week 6 (31)
Newer findings demonstrate that ultra-endurance runners fully habituated to the KD (>20 months)
experience similar baseline and post-exercise muscle glycogen levels compared to controls on a mixed-diet
(32). These studies indicate that initial depletion of muscle glycogen induced by the KD may be at least
partially reversed through habituation to the diet. Moreover, normal post-exercise glycogen repletion in KD-
adapted individuals may be attained by increased lactate-mediated hepatic glucose production i.e.
gluconeogenesis, and muscle glycogen synthase activity, especially in type II fibers (26, 33-35).
Additionally, KD-adaptation has been shown to preserve liver and muscle glycogen during exercise; KD-
adapted rats and trained humans have been shown to exhibit reduced exercising muscle and liver glycogen
degradation rates without sacrifice to endurance performance (20-22, 29, 35, 36). These evidence, though
somewhat indirect, suggest that chronic reliance on fat as a primary fuel increases its inherent rate of
oxidation, an especially useful adaptation that reduces muscle glycogen degradation while maintaining cell
energy levels during exercise (36).
Ketogenic Diet in Practice
Ketogenic Diet and Weight Management.
Perhaps the most understood and implemented application of the KD is within bariatric medicine, as obese
individuals undertaking a hypocaloric KD experience a significant reduction in weight that is vastly
attributed to fat loss with minimal loss in muscle mass (18, 37-39). Less studied, yet perhaps equally
intriguing, is apparently even a eucaloric KD may promote fat loss and lean mass preservation in both obese
and healthy weight individuals (15, 40, 41). Most recently, investigators reported that obese and overweight
individuals following either an eight-week resistance training (RT) with a eucaloric, carbohydrate restrictive
diet (<30grams/day) or RT with a conventional, hypocaloric diet saw equal improvements in fat composition
and strength (42). Driving these KD-induced anthropometric adaptations is increased sensitivity to both
insulin and thyroid hormone, which helps to limit rates of skeletal muscle catabolism during periods of
weight-loss (15, 43). These findings lend intriguing sports nutrition research opportunities for weight-
The role of the ketogenic diet in exercise performance
Evan E. Schick
Medicina Sportiva
category athletes who must reduce body mass while retaining muscle mass during competition preparation
(43). The KD could represent a healthier nutritional strategy for these athletes compared to commonplace
rapid weight loss practices such as severe caloric and hydration restriction and induction of hyperthermia.
Ketogenic Diet and Aerobic Exercise.
The manner in which KD affects aerobic performance appears to be determined by three factors: exercise
intensity, training status and length of diet habituation. Bergstrom et. al., 1967, (12) illustrated that three days
of a KD was enough to compromise submaximal endurance (75% VO2max) in healthy, untrained
individuals. Similarly, a six-week high fat diet (HFD) significantly reduced work output in untrained subjects
during a 45-minute bicycle test. The authors attributed this finding to an increased proportion of fat oxidation
observed through decreased exercising respiratory exchange ratio (RER) (40). However, the purported
sacrifice to high intensity exercise performance may represent a tradeoff for increased fatigue resistance.
Indeed, moderately obese subjects adhering to a six-week KD exhibited reduced exercise intensity but
greater stamina during a treadmill exercise test to subjective exhaustion (31). These studies suggest that
enhanced fat oxidation may not be energetically compatible with high intensity exercise but it may augment
long duration exercise.
Interestingly, aerobic performance in KD-adapted endurance athletes appears to be less susceptible
to shifts in energy substrate utilization. Initial studies in trained cyclists revealed that 4-weeks of a KD did
not affect moderate intensity (~65%VO2max) endurance exercise performance; apparently, enhanced
exercising fat oxidation rates, observed through lower RER, were able to compensate for reductions in steady
state glucose oxidation rates (36). More recently, elite ultra-endurance runners habituated (>20 months) to a
low-carbohydrate diet (LC) displayed significantly greater rates of fat oxidation and lower rates of
carbohydrate oxidation during a 180-minute run at 64% of VO2max. Peak fat oxidation rates were also
significantly greater in the LC group and were reached at a higher percentage of VO2max compared to
controls (32). Furthermore, following just two-weeks of a high fat diet (~70% fat), trained cyclists
experienced lower RER values and enhanced endurance during moderate intensity (60% VO2max) exercise
(29). More notably, HFD did not impair performance during a high-intensity (85% VO2max) time to
exhaustion test. Likewise, 6-15 days of HFD enhanced fat oxidation and decreased CHO oxidation rates in
trained cyclists while either not affecting or even improving performance during 20-100kilometer cycling
time trials (22, 35, 44). However, Zajac and colleagues (20) provide new insights revealing that competitive
off-road cyclists undergoing 4 weeks of a KD experienced reduced exercising RER concomitant to
diminished maximal workload and workload at lactate threshold (45). Collectively, current findings
surrounding the KD and aerobic exercise performance, though inconclusive, highlight the need for further
examination of how training status impacts adaptation to the KD and resultant performance. Moreover, if the
KD does not impair higher intensity aerobic intensity exercise performance (<80% VO2max), future
evidence needs to support both morphological and functional changes in mitochondria that would allow the
cell to meet the increased rate of ATP demand requisite during high intensity aerobic exercise.
Ketogenic Diet and Anaerobic Exercise.
The existing pool of knowledge vis-à-vis the KD and anaerobic performance is scarce. In fact, equivocal
results from a mere six studies and one abstract currently encompass the subject. Four studies report that the
KD negatively impacts anaerobic performance. Of these, one study utilized recreationally trained subjects
and found that KD significantly reduced isotonic strength as measured by a three-set squat repetition total at
80% 1RM (46). Two other studies utilized cycle ergometer to measure anaerobic power output in healthy
non-highly trained subjects but their results differed slightly. While one found that KD limited both mean
and peak power, the other noted only a decrement in mean power (30, 40). In the former study, the authors
noted that the reduction in mean power was mitigated when corrected for a loss in body mass in the KD
group. These findings corroborate additional findings in which well-trained cyclists subjected to 6-days of
HFD followed by 1-day of CHO loading exhibited reduced exercising fat oxidation rates and impaired high
intensity cycle sprint performance (44).
Still, three other studies provide evidence supporting the use of the KD in conjunction with strength
and power training; the most compelling of which showed that elite female gymnasts following a KD during
normal training did not exhibit impairments in muscular strength, endurance or power (41). Significantly,
this was the only investigation of athletes. Likewise, a pilot study found that KD did not deter gains in either
strength or anaerobic power in response to an 8-week periodized resistance-training regimen (47).
The role of the ketogenic diet in exercise performance
Evan E. Schick
Medicina Sportiva
One other study highlighted the clinical utility of the KD in showing that overweight women lost body fat
while maintaining lean body mass when combining a KD with resistance training (48-50)..Worth noting, two
of the aforementioned studies that approximated glycolytic flux while evaluating the effect of KD on
anaerobic power and muscular strength generated similar results. Both studies reported depressed blood
lactate levels in subjects adhering to a KD immediately following 30-second supra-maximal intensity cycling
attempt and 3 sets of squats (30, 51). The authors of each study speculated that this might account for the
observed reductions in power and strength since lactate production is positively correlated with glycolytic
capacity during high intensity efforts.
The overarching limitation of the above studies is that none allowed for adequate adaptation to the
KD, allotting a dubious task of synthesizing interpretations. Future studies must allow for at least 8-weeks
for diet adaptation before testing commences. Furthermore, significant attention must be given to how
adaptation to the KD alters intramyoceullular energetics during anaerobic exercise. Studies must specify
creatine phosphate (CP) turnover rates during sets and rest periods of anaerobic exercise as well as whether
KD affects intramyocellular CP storage levels. Finally, modalities of anaerobic activities must be diversified,
i.e. resistance based training, and should aim to better mimic “real world” anaerobic exercise.
Practical Application of the KD
Though the precise impact of ketosis on exercise performance remains unclear, practitioners looking to
integrate this nutrition strategy into their training may consider several methods. Dietary induction of ketosis
is most successful when >60% caloric energy is derived from fat and <5% is from CHO (52). Protein should
constitute a significant proportion of dietary energy (>20%) as it retards muscle wasting and amino acids
such as leucine and lysine are ketogenic (53). Upon absorption, medium chain triglycerides (MCT’s) avoid
systemic circulation and instead enter portal circulation for immediate oxidation by the liver, making MCT
oil a possible adjuvant to a KD (54). However, tolerability of MCT oil, especially at higher doses, may be
individualized, thus care should be taken when considering this method (55). Beyond the scope of nutritional
and supplemental methods, is an exciting new patent for a synthetic ketone body and ketone ester, providing
an intriguing new possibility for inducing ketosis, preventing muscle glycogen breakdown, aiding muscle
recovery and preventing muscle wasting. Before undertaking a KD, the practitioner must consider
performance goals, health and nutritional access in an effort to maximize effectiveness, adherence and safety.
Acknowledgements. The author declares no conflict of interest. The study was not funded. The results of the
present study do not constitute endorsement of the product by the author.
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Corresponding author
Evan E. Schick
Department of Kinesiology, HHS2-210
California State University, Long Beach
1250 Bellflower Ave.
Long Beach, CA 90840
Tel: (562) 985-4590
Received: September 6, 2016
Accepted: November 25, 2016
... In conclusion, the Ketogenic diet (low carbohydrate) did not result in significantly different ability or performance metrics than the comparator group. (Schick, 2016). According to Kang, Due to the individuals' decreased body weight, one study discovered a significant improvement in relative capabilities but not supreme power. ...
Several sportsmen are worried about achieving or sustaining their ideal body weight and distribution for their discipline. Players may wish to lose weight to improve effectiveness, enhance visual appeal, or participate in weight class activities. This culminates in attempts to lose body fat while decreasing muscle mass, as well as eating choices that can have serious health effects. A Ketogenic diet is rich in fat, low in carbs, and somewhat high in protein. Various nutrition-exercise combos have been evaluated in an attempt to boost oxidative stress rates while decreasing carbohydrate efficiency levels and improving overall exercise capacity. According to the findings, increasing fat availability leads to higher rates of whole-body and muscular lipid use during regular moderate-intensity aerobic activity. With significant increases in fatty acid oxidation levels, such diets regularly fail to increase stamina results in comparison to a carb diet, and nothing is understood to evaluate the impact of a Ketogenic diet on strength development. Consequently, the Ketogenic diet may be one of the most extensively researched and defined dietary regimes for losing weight. It is also becoming more popular as a long-term treatment for a variety of illnesses, including epilepsy and many others, and is a typical dietary pattern of Regional cultures. Considering these factors, as well as the reality that there are always sportsmen who choose to do, or are compelled to do, just about everything that that may provide even a slight benefit, protocols that provide that are known to be detrimental.
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This study was designed to bring new information about the hypothesis of “concurrent training” between strength and endurance which happened in high level training of elite athletes. We considered that the comparative study of the aerobic and anaerobic performance parameters of specifically trained athletes can offer practical information about these adaptation. For this purpose were analysed the results from 450 top athletes, trained in aerobic, anaerobic and mixed energogenesis sports activities, obtained during the assessment of the effort capacity. The results sustain that training a particular energetic pathway at high level can have negative or positive effects on the other one, based on the athlete`s gender. The excessive training of the aerobic effort capacity happen to the detriment of the anaerobic effort capacity for both, female and male athletes. The very high intensity, short duration training which characterizes the physical training in the alactic anaerobic trials corroborated with decreasing the maximum oxygen consumption only in the male anaerobic alactic group, while the female anaerobic groups, both alactic and lactic, registered positive correlations with the maximum oxygen consumption. Key words: effort capacity, training program, athletes, muscle fiber.
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Method: At baseline and week 8, the participants underwent body composition assessment by anthropometry, measurement of muscle thickness by ultrasound, and three strength tests using isotonic equipment. Both groups had similar reductions in body mass and fat mass as well as maintenance of fat-free mass. Muscle strength increased 14 ± 6% in the CRD group (p = 0.005) and 19 ± 9% in the CONV group (p = 0.028), with no significant differences between the groups. No significant differences were detected in muscle thicknesses within or between the groups. In conclusion, hypoenergetic diets combined with RT led to significant increases in muscle strength and were capable of maintaining muscle thicknesses in the upper and lower limbs of overweight and obese participants, regardless of the carbohydrate content of the diets.
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Background: Many successful ultra-endurance athletes have switched from a high-carbohydrate to a low-carbohydrate diet, but they have not previously been studied to determine the extent of metabolic adaptations. Methods: Twenty elite ultra-marathoners and ironman distance triathletes performed a maximal graded exercise test and a 180 min submaximal run at 64% VO2max on a treadmill to determine metabolic responses. One group habitually consumed a traditional high-carbohydrate (HC: n=10, %carbohydrate:protein:fat=59:14:25) diet, and the other a low-carbohydrate (LC; n=10, 10:19:70) diet for an average of 20 months (range 9 to 36 months). Results: Peak fat oxidation was 2.3-fold higher in the LC group (1.54±0.18 vs 0.67±0.14 g/min; P=0.000) and it occurred at a higher percentage of VO2max (70.3±6.3 vs 54.9±7.8%; P=0.000). Mean fat oxidation during submaximal exercise was 59% higher in the LC group (1.21±0.02 vs 0.76±0.11 g/min; P=0.000) corresponding to a greater relative contribution of fat (88±2 vs 56±8%; P=0.000). Despite these marked differences in fuel use between LC and HC athletes, there were no significant differences in resting muscle glycogen and the level of depletion after 180 min of running (-64% from pre-exercise) and 120 min of recovery (-36% from pre-exercise). Conclusion: Compared to highly trained ultra-endurance athletes consuming an HC diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.
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The successful treatment of malignant gliomas remains a challenge despite the current standard of care, which consists of surgery, radiation and temozolomide. Advances in the survival of brain cancer patients require the design of new therapeutic approaches that take advantage of common phenotypes such as the altered metabolism found in cancer cells. It has therefore been postulated that the high-fat, low-carbohydrate, adequate protein ketogenic diet (KD) may be useful in the treatment of brain tumors. We have demonstrated that the KD enhances survival and potentiates standard therapy in a mouse model of malignant glioma, yet the mechanisms are not fully understood. To explore the effects of the KD on various aspects of tumor growth and progression, we used the immunocompetent, syngeneic GL261-Luc2 mouse model of malignant glioma. Tumors from animals maintained on KD showed reduced expression of the hypoxia marker carbonic anhydrase 9, hypoxia inducible factor 1-alpha, and decreased activation of nuclear factor kappa B. Additionally, tumors from animals maintained on KD had reduced tumor microvasculature and decreased expression of vascular endothelial growth factor receptor 2, matrix metalloproteinase-2 and vimentin. Peritumoral edema was significantly reduced in animals fed the KD and protein analyses showed altered expression of zona occludens-1 and aquaporin-4. The KD directly or indirectly alters the expression of several proteins involved in malignant progression and may be a useful tool for the treatment of gliomas.
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This study was designed to bring new information about the hypothesis of “concurrent training” between strength and endurance which happened in high level training of elite athletes. We considered that the comparative study of the aerobic and anaerobic performance parameters of specifically trained athletes can offer practical information about these adaptation. For this purpose were analysed the results from 450 top athletes, trained in aerobic, anaerobic and mixed energogenesis sports activities, obtained during the assessment of the effort capacity. The results sustain that training a particular energetic pathway at high level can have negative or positive effects on the other one, based on the athlete`s gender. The excessive training of the aerobic effort capacity happen to the detriment of the anaerobic effort capacity for both, female and male athletes. The very high intensity, short duration training which characterizes the physical training in the alactic anaerobic trials corroborated with decreasing the maximum oxygen consumption only in the male anaerobic alactic group, while the female anaerobic groups, both alactic and lactic, registered positive correlations with the maximum oxygen consumption.
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The purpose of this study was to investigate the effects of the weight loss through 3 weeks of ketogenic diet on performance-related physical fitness and inflammatory cytokines in Taekwondo athletes. The subjects selected for this research were 20 Taekwondo athletes of the high schools who participated in a summer camp training program. The subjects were randomly assigned to 2 groups, 10 subjects to each group: the ketogenic diet (KD) group and the non-ketogenic diet (NKD) group. Body composition, performance-related physical fitness factors (2,000 m sprint, Wingate test, grip force, back muscle strength, sit-up, 100 m sprint, standing broad jump, single leg standing) and cytokines (Iinterleukin-6, Interferon-γ, tumor necrosis factor-α) were analyzed before and after 3weeks of ketogenic diet. No difference between the KD and NKD groups in weight, %body fat, BMI and fat free mass. However, the KD group, compared to the NKD group, finished 2,000 m sprint in less time after weight loss, and also felt less fatigue as measured by the Wingate test and showed less increase in tumor necrosis factor-α. This result suggests that KD diet can be helpful for weight category athletes, such as Taekwondo athletes, by improving aerobic capacity and fatigue resistance capacity, and also by exerting positive effect on inflammatory response.
The effects of adaptation to a high-fat diet on endurance performance are equivocal, and there is little data regarding the effects on high-intensity exercise performance. This study examined the effects of a high-fat/moderate protein diet on submaximal, maximal, and supramaximal performance. Twenty non-highly trained men were assigned to either a high-fat/moderate-protein (HFMP; 61 % fat) diet (n = 12) or a control (C; 25% fat) group (n = 8). A maximal oxygen consumption test, two 30-s Wingate anaerobic tests, and a 45-min timed ride were performed before and after 6 weeks of diet and training. Body mass decreased significantly (-2.2 kg; p less than or equal to .05) in HFMP subjects. Maximal oxygen consumption significantly decreased in the HFMP group (3.5 +/- 0.14 to 3.27 +/- 0.09 L (.) min(-1)) but was unaffected when corrected for body mass. Perceived exertion was significantly higher during this test in the HFMP group. Main time effects indicated that peak and mean power decreased significantly during bout 1 of the Wingate sprints in the HFMP (-10 and -20%, respectively) group but not the C (-8 and -16%, respectively) group. Only peak power was lower during bout 1 in the HFMP group when corrected for body mass. Despite significantly reduced RER values in the HFMP group during the 45-min cycling bout, work output was significantly decreased (-18%). Adaptation to a 6-week HFMP diet in non-highly trained men resulted in increased fat oxidation during exercise and small decrements in peak power output and endurance performance. These deleterious effects on exercise performance may be accounted for in part by a reduction in body mass and/or increased ratings of perceived exertion.
Ketone bodies acetoacetate (AcAc) and D-β-hydroxybutyrate (βHB) may provide an alternative carbon source to fuel exercise when delivered acutely in nutritional form. The metabolic actions of ketone bodies are based on sound evolutionary principles to prolong survival during caloric deprivation. By harnessing the potential of these metabolic actions during exercise, athletic performance could be influenced, providing a useful model for the application of ketosis in therapeutic conditions. This article examines the energetic implications of ketone body utilisation with particular reference to exercise metabolism and substrate energetics.