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

Abstract

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

Full text

Citation: Khouri, H.; Ussher, J.R.;
Aguer, C. Exogenous Ketone
Supplementation and Ketogenic
Diets for Exercise: Considering the
Effect on Skeletal Muscle Metabolism.
Nutrients 2023,15, 4228. https://
doi.org/10.3390/nu15194228
Academic Editor: Antoni Sureda
Received: 1 September 2023
Revised: 23 September 2023
Accepted: 25 September 2023
Published: 30 September 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
nutrients
Review
Exogenous Ketone Supplementation and Ketogenic Diets for
Exercise: Considering the Effect on Skeletal Muscle Metabolism
Hannah Khouri 1,2, John R. Ussher 3and Céline Aguer 1,2,4,*
1Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa,
Ottawa, ON K1N 6N5, Canada; hkhou006@uottawa.ca
2Institut du Savoir Montfort, Hôpital Montfort, Ottawa, ON K1K 0T2, Canada
3Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2H5, Canada;
jussher@ualberta.ca
4Department of Physiology, Faculty of Medicine and Health Sciences, McGill University–Campus Outaouais,
Gatineau, QC J8V 3T4, Canada
*Correspondence: celine.aguer@mcgill.ca
Abstract:
In recent years, ketogenic diets and ketone supplements have increased in popularity,
particularly as a mechanism to improve exercise performance by modifying energetics. Since the
skeletal muscle is a major metabolic and locomotory organ, it is important to take it into consideration
when considering the effect of a dietary intervention, and the impact of physical activity on the
body. The goal of this review is to summarize what is currently known and what still needs to be
investigated concerning the relationship between ketone body metabolism and exercise, specifically
in the skeletal muscle. Overall, it is clear that increased exposure to ketone bodies in combination with
exercise can modify skeletal muscle metabolism, but whether this effect is beneficial or detrimental
remains unclear and needs to be further interrogated before ketogenic diets or exogenous ketone
supplementation can be recommended.
Keywords:
ketone bodies; ketogenic diet; ketone supplements; skeletal muscle; exercise; exercise
performance; metabolism
1. Introduction
Ketone bodies (hereinafter referred to as ketones) are produced by the liver during
periods of fasting or low carbohydrate availability to provide an alternative source of
energy to glucose and fatty acids [
1
,
2
]. Specifically, the ketones
β
-hydroxybutyrate (
β
OHB)
and acetoacetate are synthesized from acetyl-CoA derived from hepatic fatty acid oxidation,
then they are exported to extra-hepatic tissues primarily for oxidation. The brain is a
major consumer of ketones during fasting, but other tissues such as the skeletal muscle
(hereinafter referred to as muscle) can also oxidize ketones for energy. This is advantageous
because it limits muscle proteolysis to generate amino acids, which can feed hepatic
glucose production. Importantly, the rate-limiting enzyme of ketogenesis is HMGCS2 (3-
hydroxymethylglutaryl-CoA synthase 2), and the enzymes BDH (
β
OHB dehydrogenase),
SCOT (succinyl-CoA:3-oxoacid-CoA transferase; gene name Oxct1) and ACAT (acetoacetyl
CoA thiolase) sequentially catalyze the series of steps in ketone body oxidation, where
β
OHB can be reversibly converted to acetoacetate by BDH. Of note,
β
OHB exists as
two different enantiomers, D-
β
OHB and L-
β
OHB [
3
]. The literature suggests that D-
β
OHB is involved in ketogenesis and ketolysis (and is therefore oxidized to produce
adenosine triphosphate (ATP)), whereas the role of L-
β
OHB and how it is produced
remains unclear [4].
In recent years, ketogenic diets (hereinafter referred to as keto diets) have increased
in popularity. The diet consists of very low levels of carbohydrates in combination with
high levels of fat and moderate levels of protein. As a result, the body enters a state of
Nutrients 2023,15, 4228. https://doi.org/10.3390/nu15194228 https://www.mdpi.com/journal/nutrients

Nutrients 2023,15, 4228 2 of 22
ketosis, where it becomes dependent on burning fat and ultimately synthesizing ketones
for energy [
5
]. The levels of ketones in the organism can also be increased exogenously
without the need to limit carbohydrate intake via supplementation with ketone esters.
Ketone esters are typically consumed in a beverage and have been previously proven to
enter the bloodstream to temporarily increase circulating levels of ketones [6].
It has been proposed that a keto diet or exogenous ketone supplementation may be
beneficial with respect to exercise [
7
,
8
]. This hypothesis is based mainly on the presumption
that increased ketolysis could alter muscle fuel selection during exercise by favoring lipid
metabolism over carbohydrate metabolism. Our bodies also have a limited capacity to store
carbohydrates as glycogen, relative to the capacity to generate a lipid reserve. Therefore,
increasing fat utilization may be a mechanism to increase the amount of energy available
during exercise, especially in endurance activities. As such, a variety of studies (which
will be highlighted in this review) have investigated the potential effect of increased
ketolysis on exercise performance and the associated metabolic adaptations (e.g., muscle
glycogen). When considering the impact of a keto diet on metabolism and exercise, the
muscle is an important tissue to study, as it accounts for the majority of post-prandial
glucose uptake [
9
]. The muscle is equally a critical tissue to consider when investigating
factors related to physical activity, since it is required for locomotion [
10
]. Therefore, this
review will summarize what is known to date regarding the relationship between increased
ketolysis and exercise, with an emphasis on their effects on muscle metabolism.
2. Effect of Exercise on Muscle Ketone Body Metabolism
Parameters linked to ketone body metabolism include muscle ketolytic gene expres-
sion, enzyme activity and rates of ketolysis. Existing literature regarding the effect of
exercise and increased exposure to ketone bodies on these factors is outlined below. To
begin, the reported effect of a keto diet and exercise on the muscle expression of enzymes
involved in ketone body metabolism is variable. A 12-week keto diet (88% fat, 11% protein
and 1% carbohydrates) suppressed Oxct1 mRNA expression in the gastrocnemius muscle of
male mice (relative to a standard diet), but the combination of the keto diet and eight weeks
of treadmill exercise had no additional effect on Oxct1 expression [
11
], suggesting that
treadmill training does not counteract the negative effect of a keto diet on Oxct1 expression,
at least in mice. However, the same mice exposed to both a keto diet and exercise showed an
increased expression of Hmgcs2 mRNA in the gastrocnemius muscle. Meanwhile, exercise
alone or the keto diet alone did not alter the expression Hmgcs2. Therefore, the combination
of exercise training and a keto diet seems to have a positive effect on the expression of
enzymes involved in ketogenesis in mice, yet it remains unknown whether the muscle can
support ketogenesis even if Hmgcs2 is expressed. Next, an eight-week keto diet (76.1% fat,
8.9% protein and 3.5% carbohydrates) combined or not with exercise did not alter Oxct1
mRNA expression in the gastrocnemius or soleus muscle of male mice [
8
]. Yet, the mRNA
expression of Bdh was downregulated by the keto diet in the gastrocnemius muscle (mixed
muscle) but upregulated in the soleus (oxidative muscle). Although this effect was not
dependent on exercise, it highlights the potential variability in gene expression in different
muscle types in response to a keto diet or exercise. Further, the shorter-term keto diet may
explain why different results were reported as compared to the 12-week keto diet described
above. Since medium-chain triacylglycerols (TAGs) are believed to be more ketogenic
due to rapid uptake into the liver, a third study further separated an 8-week regimen
into either a keto diet with long-chain or medium-chain TAGs, with regular swimming
exercise. In general, male rats who performed the exercise regimen had higher SCOT
protein expression across all diets [
12
]. Further, SCOT protein expression was increased
in the epitrochlearis muscle with both keto diets relative to a control diet, but to a greater
extent with the medium-chain TAGs. This conclusion suggests that the composition of a
keto diet is an important variable to consider. Other studies took a different approach and
measured the effect of acute exercise on ketolytic gene expression independently of diet.

Nutrients 2023,15, 4228 3 of 22
For example, a single bout of treadmill running did not alter Bdh,Oxct1 or Acat expression
in mouse quadriceps muscle [13].
In addition to their expression, a small selection of studies investigated the impact of
exercise on the activity of enzymes involved in ketolysis. Following a 10-week treadmill
running program, SCOT activity was increased in the gastrocnemius muscle (mixed muscle)
of male rats [
14
]. A comparable study reported the same results, but they also measured
the activity of BDH and ACAT, which were also increased in the gastrocnemius muscle as
a result of the exercise regimen [
15
]. On the other hand, following 15 weeks of treadmill
running in male rats, SCOT activity was increased in the diaphragm (mixed muscle), but
no differences were reported in the intercostal muscle (glycolytic muscle) [
16
]. It should
be noted that these are respiratory muscles, not muscles involved in movement during
exercise. All together, these studies suggest that exercise increases SCOT activity, but
there may be variability between muscle types, potentially with a less important effect
observed in glycolytic muscles. Interestingly, it is also possible that metabolic diseases
impact the effect of exercise on SCOT activity, as a 10-week exercise program in diabetic
rats increased gastrocnemius SCOT activity to a greater extent than in rats without diabetes
(when measured relative to their sedentary counterparts) [
14
]. The greater increase is likely
because sedentary diabetic rats had lower SCOT activity than the rats without diabetes,
but regardless, the observation implies that exercise may protect against decreased muscle
ketolysis induced by diabetes (which may be connected to diabetic hyperketonemia).
Lastly, there have also been reports on the impact of exercise on the rate of ketone body
utilization in the muscle. For example, 12 weeks of treadmill running increased oxidation of
acetoacetate and D,L-
β
OHB in isolated gastrocnemius muscle from male rats [
15
]. Similarly,
the uptake of acetoacetate alone and a combination of acetoacetate and
β
OHB was increased
in perfused hindlimb muscles of trained relative to untrained male rats (although no
effect was reported for the uptake of
β
OHB alone) [
17
]. Contrarily, a single bout of
treadmill running did not alter maximal acetoacetate or
β
OHB supported respiration in
permeabilized fibers from the gastrocnemius of male rats [
18
]. It is possible that a prolonged
exercise program is necessary to induce alterations in ketone body oxidation or ketolytic
gene expression and activity, and the length of a keto diet or exercise program should be
taken into consideration.
Other studies have measured the levels of ketones in the muscle following exercise,
although it is unclear whether increased muscle ketones are indicative of increased ketone
body uptake and oxidation or decreased muscle ketolysis. For example, in male endurance
athletes who consumed a beverage supplemented with ketone esters during an exercise test,
the levels of D-
β
OHB in the muscle were higher 1 h post-exercise (relative to athletes who
consumed a beverage without ketone esters) [
7
]. However, the levels were also higher pre-
exercise, which implies that the D-
β
OHB may have been minimally oxidized by the muscle
during the activity. As another example, in
in vitro
C2C12 mouse muscle cells exposed to
forskolin (a cAMP pathway activator to mimic exercise), levels of
β
OHB were higher in
cell lysates and culture media than in control cells [19]. To the best of our knowledge, this
is the only study that suggests that the muscle may produce
β
OHB. Since the study cited
above concluded that Hmgsc2 is expressed in the gastrocnemius muscle of male mice, it
supports the possibility that the muscle is capable of undergoing ketogenesis, a hypothesis
that should be explored in more depth in the future.
To summarize, it appears that exercise training increases the expression of enzymes
involved in ketone body metabolism, as well as their activity and rates of ketolysis in
the muscle. However, variables such as the length and composition of the keto diet, and
the muscle type in question should be considered. Additionally, it should be noted that
the majority of studies on ketones, exercise and the muscle are conducted exclusively in
male rodents. However, although only measured in the plasma and not the muscle, it was
reported that the levels of serum acetoacetate and
β
OHB were higher in female than male
mice following a bout of endurance exercise [
13
]. This conclusion highlights the need to
introduce biological sex as a variable in experiments similar to the ones described here.

Nutrients 2023,15, 4228 4 of 22
Further, almost all of the studies presented in this section were performed in rodents or
rodent cell lines. As such, no conclusions can be drawn regarding the effect of ketone
bodies on ketolytic gene expression and enzyme activity in human muscle, a limitation that
should be investigated in future experiments.
3. Muscle PDK4 Activation Following a Keto Diet and Exercise
Pyruvate dehydrogenase (PDH) is a mitochondrial enzyme complex that converts
pyruvate into acetyl-CoA, thereby controlling the entry of glucose into the Krebs cycle. In
the muscle, PDH is inhibited by phosphorylation via pyruvate dehydrogenase kinase 4
(PDK4). Of relevance, PDK4 expression has been shown to be enhanced in response to
an acute bout of exercise, as well as in response to fasting in order to spare glucose when
muscle glycogen levels are low [
20
]. Since keto diets are low in carbohydrates, they may
result in a lack of glucose available to build muscle glycogen, which could activate PDK4.
PDK4 expression may be also increased as a result of the high-fat nature of a keto diet,
which can activate PPAR (peroxisome proliferator-activated receptor)
α
and induce the
transcription of PDK4 [
21
]. It is unknown whether ketones (which are derived from fatty
acids) can exert the same effect. In any case, several studies have reported that PDK4
expression was increased in the muscle in response to a keto diet or endurance exercise.
Namely, in the gastrocnemius muscle collected from male mice following a four-week keto
diet (with an unspecified composition) and both a single exhaustive treadmill running and
weight-bearing swimming test, the mRNA expression of Pdk4 was upregulated relative to
a control diet [
22
]. Pdk4 gene expression was also increased in the quadriceps muscle of
male mice on a six-week high-fat keto diet (83.9% fat, 16.1% protein and 0% carbohydrates)
relative to a control diet (although there was no additional effect of a three-week treadmill
running regimen, nor was there any differences in PDH activity or pyruvate oxidation) [
23
].
PDK4 protein expression was increased with both diet and swimming exercise in
male rats on the long-chain TAG keto diet described above (relative to the medium-chain
TAG or control diet) [
12
]. However, no effect was observed with the medium-chain TAGs
in the epitrochlearis muscle. As such, the authors proposed that a medium-chain TAG
keto diet may avoid inhibiting the glycolytic pathway. Based on this proposition, it is
possible that PDK4 is only activated in response to low glycogen levels, rather than a keto
diet or exercise themselves. Since medium-chain TAGs are more rapidly oxidized by the
liver, muscle glycogen could be somewhat spared due to quicker energy derivation from
fatty acid oxidation and ketogenesis, which could explain why the diet did not alter PDK4
activity (relative to long-chain TAGs). The results showing increased PDK4 activity were
maintained in a clinical study, which found that a 10-day keto diet (80% fat, 15% protein
and 5% carbohydrates) increased PDK4 protein content in the vastus lateralis muscle
of participants who perform at least 6 h of endurance exercise per week (relative to a
control diet) [
24
]. However, interestingly, 10 days of exogenous D-
β
OHB supplementation
did not increase PDK4 expression in a similar group of participants, which raises the
possibility that the exogenous effect of ketones does not parallel the endogenous effects. It
should be noted that the participants consumed a control (i.e., not keto) diet while taking
the supplements, providing them access to carbohydrates. This supports the hypothesis
outlined above that PDK4 is increased in response to depleted muscle glycogen and not a
keto diet or supplementation. Consistent with this hypothesis is a study that concluded that
incubating muscle with ketones does not allow for PDH activation. In isolated epitrochlearis
muscle from male mice following a single bout of swimming, there was no impact of a 2 h
incubation with 4 mM D,L-
β
OHB on the phosphorylation of PDH at Ser293 (an indicator
of an activated state) [
25
]. A final study reported no change in PDK4 in response to ketones
and exercise. Specifically, Pdk4 mRNA expression was not altered in the mitochondria
isolated from the gastrocnemius muscle of male mice on a six-week keto diet (69.5% fat,
20.2% protein, 10.3% carbohydrates) combined with a resistance running wheel exercise
regimen [
26
]. This study differs from those presented above with respect to the type of
exercise (resistance rather than endurance), which may indicate that endurance exercise is

Nutrients 2023,15, 4228 5 of 22
also linked to changes in PDK4 expression. It is also important to note that the diet in this
study was higher in carbohydrates (10% vs. 0–5% in studies discussed above), which could
theoretically result in a lower muscle glycogen depletion in response to exercise and thus,
no effect in PDK4 expression.
Overall, studies that report no change in PDK4 expression involve either resistance
exercise or ketone supplementation. Meanwhile, endurance exercise is consistently impli-
cated in studies reporting increases in PDK4 expression in subjects or rodents on a keto
diet. Therefore, parameters such as the type of exercise or the composition of the diet
may influence PDK4 expression. In any case, it remains unclear whether increased PDK4
expression connected to a keto diet or exercise leads to an impact on PDH activity or glu-
cose metabolism, a question that could be investigated in future studies. Further, whether
decreased muscle glycogen is in fact the mechanism for increases in PDK4 expression in
response to a keto diet and/or an exercise training regimen should be clarified.
4. Muscle Glycogen Stores Following Exercise and Exogenous or Endogenous
Ketone Supplementation
Muscle glycogen is a primary energy source during high-intensity exercise and is
typically depleted following an intense exercise bout or a very long endurance exercise [
27
].
Comparably, prolonged periods of decreased carbohydrate availability due to fasting are
known to decrease muscle glycogen levels [
28
]. To begin, it has generally been concluded
that endurance exercise training protects against the loss of muscle glycogen due to a
keto diet. For example, after four weeks on a keto diet (88% fat, 11% protein and 1%
carbohydrates), glycogen in the quadriceps of male mice was decreased relative to a
control diet [
11
]. However, when the diets were extended by an additional eight weeks in
combination with regular treadmill running (5 times per week, 30 min each time), there
were no differences in muscle glycogen in mice on the keto diet and exercise program
versus the control diet and exercise program (measured at least 24 h after the last bout
of exercise). Therefore, it appears that the endurance program protected against muscle
glycogen loss due to the keto diet. Consistently, in a comparable study using a six-week
keto diet (83.9% fat, 16.1% protein and 0% carbohydrates) with a three-week treadmill
running program during the second half of the diet (5 times per week, 1 h each time),
training increased quadriceps glycogen levels in both diets but there was no difference
between diets [
23
]. Similarly, in male endurance runners consuming a low carbohydrate
diet for at least six months (>60% fat, <20% carbohydrates), there were no differences
in muscle glycogen at rest, following a 180 min endurance running test (64% VO
2
max),
nor following a subsequent 2 h recovery period relative to participants who had been
consuming a high carbohydrate diet [
29
]. Overall, this group of studies suggests that
increased ketolysis in combination with endurance training does not alter muscle glycogen
levels relative to a control diet and the same training program. To the same point, in the
muscle of the male rats given the keto diets with medium or long-chain TAGs described in
previous sections, glycogen in the epitrochlearis muscle was lower with both keto diets
relative to a control diet [
12
]. However, with swimming exercise, only the long-chain TAG
diet decreased muscle glycogen relative to a control diet and exercise (measured at least
20 h following the last bout of exercise). This finding is consistent with the conclusions
outlined above, since endurance exercise protects against muscle glycogen loss due to a
medium-chain TAG diet. However, the fact that the same conclusion was not reported
with the long-chain TAG diet supports the hypothesis outlined in the previous section that
medium-chain TAGs spare muscle glycogen, and therefore, did not alter PDK4 expression.
On the other hand, a 12-week keto diet (with an unspecified composition) in combi-
nation with a 2-week training program (high-intensity interval training and periodized
resistance and power exercises, plus endurance training once a week) resulted in decreased
muscle glycogen in a group of military personnel, but stable levels in individuals who
consumed a control diet with the exercise regimen [
30
]. The exercise program involved
mainly resistance activities, which may explain why the conclusion differs from the effect

Nutrients 2023,15, 4228 6 of 22
of endurance exercise and a keto diet on muscle glycogen levels outlined above. Of note, in
the previous section, it was postulated that PDK4 expression was increased with endurance
exercise, and in response to low glycogen levels. This is contradictory to the general conclu-
sion in this section that endurance exercise may spare muscle glycogen. Therefore, muscle
glycogen levels and PDH should be investigated in the same studies or subjects going
forward to better understand the effect of ketones on glucose metabolism.
For comparison, a second set of studies investigated the impact of endogenous ketone
supplementation and exercise on muscle glycogen levels. For example, the addition of
ketones to a carbohydrate-rich beverage consumed before and during a 2 h bicycle exercise
at 45% VO
2
max, allowed male endurance athletes to have a smaller decrease in their muscle
glycogen reserves [
7
]. Similarly, the consumption of a drink with D-
β
OHB allowed male
athletes to replenish their muscle glycogen levels faster following an overnight fast and an
interval cycling exercise [
31
]. Likewise, the regular consumption of a ketone ester drink in
physically active males who followed a three-week endurance and high-intensity interval
training allowed for maintenance of their muscle glycogen levels following a 30 min time
trial while muscle glycogen was decreased in participants who did not receive the ketone
ester drink [
32
]. In contrast to the studies with a keto diet detailed above, this group of
studies suggests that exogenous ketone supplementation can spare muscle glycogen loss
due to either one exercise bout or exercise training. With that being said, a pair of studies
indicate that ketone ester supplementation had no effect on muscle glycogen. One study
subjected physically active males to a glycogen-depleting exercise involving the leg, then
provided them with a ketone ester drink and found that this did not alter muscle glycogen
levels at the end of a 5 h recovery period [
33
]. The same conclusion was made at the end of
a 3 h stimulated cycling race by male cyclists, who received D-
β
OHB before and during the
activity [
34
]. To determine the direct effect of ketones on muscle glycogen levels, isolated
epitrochlearis muscles from male mice following a single 60 min swimming exercise were
exposed to 1, 2 and 4 mM of D,L-
β
OHB for 2 h. Only 4 mM of D,L-
β
OHB increased
glycogen levels [
25
]. Therefore, it is possible that a higher concentration of ketones in the
muscle is needed to influence muscle glycogen levels, whereas lower concentrations do not
exert the same effect.
In conclusion, the effect of ketones and exercise on muscle glycogen levels are variable
and appear to depend particularly on whether ketone body levels are being increased
exogenously or endogenously. Additionally, it is possible that ketones have a signaling
effect during exercise, possibly to increase the storage of glycogen during the recovery
phase or decrease the use of muscle glycogen during the activity, therefore reducing the loss
of glycogen. This hypothesis would also support the postulation outlined in the previous
section that PDK4 is activated in response to low muscle glycogen levels.
5. Increased Ketolysis as a Potential Mechanism to Alter Exercise Performance
There have been several investigations into the effect of keto diets or exogenous
ketone supplementation on exercise performance, with mixed results. To begin, studies
implicating human participants and endurance exercise tests have reported a decrease
in exercise performance following a keto diet. Namely, a three-day keto diet (50% fat,
45% protein and 5% carbohydrates) decreased mean power output during two 30 s tests on
an exercise bike in male participants [
35
] and a 4-week keto diet (77% fat, 19% protein and
4% carbohydrates) decreased time to exhaustion on an incremental cycling test (an increase
of 30 W every 4 min until 120 W) in female participants [
36
]. These results were maintained
in physically active participants following a 10-day keto diet (80% fat, 15% protein and
5% carbohydrates): performance on an incremental cycling test (90 min at 70% VO
2
max,
followed by incremental increases to fatigue) was decreased relative to a control diet [
24
].
On the other hand, an eight-week keto diet (approximately 68% fat, 25% protein and
5% carbohydrates) did not change performance on bench press and squat tests in male
bodybuilders [
37
]. Since this study measured the effect of the keto diet on resistance
exercise performance, this could explain why the conclusion differs from the endurance-

Nutrients 2023,15, 4228 7 of 22
type studies outlined above. Next, in human participants, an eight-week cyclical keto
diet (keto diet on weekdays, high carbohydrate diet on weekends) combined with regular
strength and aerobic workouts increased performance on certain strength exercises (relative
to baseline) [
38
]. The improvement associated with the cyclical keto diet may be due to
the workout program administered to the participants rather than the diet itself, but the
cyclical design could warrant further investigation in comparison to a continuous keto diet
with respect to exercise performance.
Secondly, studies using rodents have shown that a period of increased ketolysis had
no impact on endurance exercise performance. As an example, a four-week keto diet (with
an unspecified composition) in male mice did not change running distance or time on an
exhaustive treadmill running test, nor swimming time on an endurance swimming test [
22
].
Similarly, while male rats consumed a six-week keto diet (69.5% fat, 20.2% protein and
10.3% carbohydrates) and had access to a voluntary running wheel, there was no difference
in cumulative running distance relative to mice on a control diet [
39
]. The same conclusion
was also drawn in female mice following an 8 h fast to induce ketosis: exercise duration
in an endurance treadmill running test was unchanged relative to mice who had not
fasted [
40
]. To finish summarizing the reported effect of a keto diet on exercise performance,
one report was made that a keto diet may contribute to improved exercise performance.
Specifically, an eight-week keto diet (76.1% fat, 8.9% protein and 3.5% carbohydrates) led to
a longer running time in male rats during an exhaustive running test (relative to a control
diet) [
41
]. The keto diet lasted longer than the regimens described above, which may
indicate that longer-term keto diets are needed to influence endurance capacity in rodents.
For comparison, a selection of studies also measured the effect of endogenous ketone
supplementation on exercise performance. In the study cited above that reported a decrease
in exercise capacity in active participants on a 10-day keto diet, supplementation of a
regular diet with D-
β
OHB for 10 days had no effect on performance in the cycling test [
24
].
Similarly, consumption of D-
β
OHB by male cyclists did not affect power output during
a subsequent 3 h stimulated race [
34
], a conclusion that was replicated in another group
of male cyclists administered a ketone ester drink during the race [
42
]. Together, these
studies suggest that ketone supplementation does not affect endurance performance in
human participants. Contrarily, in physically active males, three weeks of endurance
and high-intensity interval training in combination with a ketone ester drink resulted in
increased power output in the final 30 min of a 2 h endurance activity [
32
]. Likewise,
two weeks of D,L-
β
OHB supplementation in male mice resulted in increased distance,
time to exhaustion and maximal speed on a weekly treadmill test [
43
]. Yet, this increase
was not maintained after a total of six weeks. Two hypotheses can be drawn from this
conclusion: the effect of supplementation with D-
β
OHB differs from that of D,L-
β
OHB and
that ketone supplementation may only have a short-term influence on exercise performance.
An investigation using male endurance athletes also found that consuming a beverage with
40% of calories coming from ketone esters (relative to 100% carbohydrates) led to increased
distance covered in a time trial that was preceded by a 60 min cycle [
7
]. Although the
increase was minor (2%), the increased carbohydrate composition of the beverage may be
what allowed for the positive impact on endurance exercise performance.
Interestingly, one study took a thoughtful approach and measured exercise capacity
in male mice with a muscle-specific SCOT knockout. In this case, the knockout mice ran
for the same time and distance during a time-to-exhaustion treadmill test as wild-type
mice, implying that preventing muscle ketone body oxidation did not impact exercise
capacity [
44
]. Ketones have also been found to exert signaling in addition to metabolic
effects [
45
]; therefore, using muscle SCOT knockout mice would be an interesting addition
to future investigations on the relationship between ketones and exercise, as it could assist
in concluding whether ketone body oxidation is necessary for potential metabolic effects
induced by exercise.

Nutrients 2023,15, 4228 8 of 22
6. Alterations in AMPK and PCG1αActivation Following an Exercise and Keto Regimen
It is well known that AMP-activated protein kinase (AMPK) is an energy-sensing
enzyme, that is activated by phosphorylation in most tissues, including the muscle, to gen-
erally stimulate energy-replenishing processes. Exercise is a prominent activator of AMPK,
as are high levels of AMP relative to ATP during fasting [
46
]. Yet of relevance to this review,
whether increased muscle ketolysis induces alterations in AMPK activation or activity has
not been elucidated. However, some studies have investigated the relationship between
AMPK, ketones and exercise in the muscle. To begin, one study found that a six-week
high-fat, no-carbohydrate diet (83.9% fat, 16.1% protein and 0% carbohydrates) combined
with a three-week treadmill running exercise regimen increased levels of phosphorylated
AMPK in the quadriceps muscle of male mice relative to mice subjected to the same exercise
regimen, but with a control diet [
23
]. In contrast, a single resistance exercise test following a
six-week keto diet (69.5% fat, 20.2% protein and 10.3% carbohydrates) in male rats did not
alter the levels of phosphorylated AMPK in the gastrocnemius muscle [
39
]. The variable
length (three weeks versus a single bout) and type (endurance versus resistance) of the exer-
cise, but also the difference in the diet composition (more carbohydrates in the second study)
could explain the different conclusions between these studies in rodents. Furthermore, a
clinical investigation of male volunteers involved in regular physical activity provided
mixed results. The participants consumed a ketone ester drink during the recovery period
following a glycogen-depleting exercise protocol in the leg, then muscle biopsies were
taken to measure AMPK phosphorylation. AMPK phosphorylation was decreased 90 min
post-exercise, but there was no difference 5 h post-exercise relative to participants who did
not consume the ketone ester drink [
33
]. This result may be different than the increased
phospho-AMPK levels observed in the rodent studies described above since the study used
human participants, and they were administered a single ketone supplement following
the bout of exercise (rather than a longer term keto diet which preceded muscle collection).
Comparably, the epitrochlearis muscle was harvested from male mice following a 60 min
swimming exercise, then subjected to 4 mM of D,L-
β
OHB ex vivo. Exposure to D,L-
β
OHB
for 15 min decreased the phosphorylation of AMPK and ACC (acetyl-CoA carboxylase, a
downstream target of AMPK), but not after 2 h [
25
]. As such, it is possible that increased
exposure to ketones following exercise results in only a brief decrease in muscle AMPK
activity, but as the ketone supply dwindles, AMPK activation begins to increase.
Comparably to AMPK, peroxisome proliferator-activated receptor-
γ
coactivator
1-alpha
(PGC1
α
) is a transcriptional coactivator that regulates energy metabolism, and its expres-
sion is enhanced by exercise in the muscle [
47
]. Although the results are limited, the effect
of a keto diet and exercise on muscle PGC1
α
has been investigated, with consistent results.
Pgc1
α
gene expression was enhanced in the gastrocnemius and soleus muscle of male mice
following an eight-week exercise program, but there was no additional effect of a keto diet
(76.1% fat, 8.9% protein and 3.5% carbohydrates) combined with the exercise [
8
]. The same
conclusion was drawn by a similar study that also used the gastrocnemius muscle of male
mice following six weeks on a keto diet (69.5% fat, 20.2% protein and 10.3% carbohydrates)
and an exercise program [
26
]. To a different conclusion, a six-week high-fat diet with no
carbohydrates (83.9% fat, 16.1% protein and 0% carbohydrates) combined with three weeks
of exercise increased Pgc1
α
gene expression in the quadriceps muscle of male mice, but the
same effect was not seen with a control diet [
23
]. Since all three of these studies used male
mice and a similar type of exercise (running on a treadmill or a resistance-loaded wheel),
the variability may be due to the fact that the study which reported an increase in Pgc1
α
expression as a result of the keto diet did not subject the mice to the exercise program for the
whole length of the keto diet (as was the case for the pair of studies reporting no effect of a
keto diet on Pgc1
α
). In spite of these results, in the absence of studies investigating the effect
of ketones themselves on the muscle expression of PGC1
α
(e.g., exogenous supplements or
ex vivo exposure), it is unclear whether PGC1
α
is increased due to the high-fat component
of a keto diet, low muscle glycogen levels or as a direct result of increased ketolysis or
ketone levels.

Nutrients 2023,15, 4228 9 of 22
Overall, it is clear that ketones and exercise can act on regulators of energy-sensing
pathways (AMPK and PGC1
α
). However, it is not clear whether there is an additional
effect when they are considered in combination, and factors such as the type and length of
exercise, whether ketones are increased pre- or post-exercise, and the length of time post
ketone supplementation should be taken into consideration in future studies.
7. Influence of Increased Exposure to Ketones on Glucose Metabolism
In a post-prandial period (when blood glucose is high), insulin signals through insulin
receptors in the muscle, which leads to the phosphorylation and activation of a group of
proteins including IRS1 (insulin receptor substrate) and AS160 (Akt substrate of 160 kDa) [
9
].
This enables translocation of GLUT4 (glucose transporter type 4) to the membrane, and
glucose uptake into muscle cells. Given the shift away from glucose metabolism that is
essential to a keto diet, it is important to consider the impact on enzymes connected to
glucose oxidation. One study found that a 10-day keto diet (80% fat, 15% protein and
5% carbohydrates) in combination with at least 6 h of physical activity per week resulted in
increased plasma glucose and insulin levels following a glucose tolerance test. Although
not specific to the muscle, it raises the possibility that keto diets may have a negative
impact on insulin sensitivity. In contrast, exogenous supplementation of a normal diet with
ketones did not produce the same effect [
24
]. It is thus possible that the negative effect of
the keto diet on glycemia was due to the increased lipid content of the diet, rather than the
ketones themselves, and that the effect of exogenous ketones differs from that of a keto diet.
To begin, a collection of studies investigated the effect of keto diets on factors linked to
glucose metabolism. Namely, in trained male cyclists who had been on low carbohydrate,
high fat diets (with variable compositions) for at least six months: relative to participants
on a control diet, GLUT4 and IRS1 protein content was decreased in the muscle [
48
]. On
the other hand, another study found that ketones and exercise had no effect on muscle
glucose metabolism. In particular, a 6-week keto diet in male mice found that regular
running exercise increased GLUT4 gene expression in the gastrocnemius muscle, but that
there was no additional effect of the keto diet relative to a control diet [
26
]. The shorter
time frame for the keto diet could explain the difference in results: it is possible that keto
diets are more detrimental to the muscle in the long term. Interestingly, exercise may
protect against keto diet-related decreases in GLUT4 expression, as a 12-week keto diet
(88% fat, 11% protein and 1% carbohydrates) without exercise resulted in decreased gene
expression of GLUT4 and pyruvate kinase (which catalyzes the last step in glycolysis) in
the quadriceps muscle of male mice, but this effect was counteracted by combining the diet
with eight weeks of treadmill running [
11
]. Taken together, these studies indicate that keto
diets may be negatively impacting factors related to muscle glucose metabolism. However,
the persistence of this observation in the long term or following the cessation of the keto
diet is not known, nor is whether exercise can counteract these potential negative effects.
Further, it is well understood that high-fat diets can induce muscle insulin resistance,
which is a cause for concern due to the fact that keto diets are high in fat, and therefore,
a potential mechanism for any negative effects of a keto diet on glucose metabolism [
49
].
Another potential mechanism for these observations is that the low carbohydrate content
of keto diets can influence GLUT4 protein levels or other parameters linked to glucose
metabolism. In support of this postulation, previous studies have shown that while a
high-fat diet decreased muscle GLUT4 expression, a high-calorie carbohydrate diet did not
exert the same effect in mice [
50
]. Similarly, a four-week high carbohydrate, fat-restricted
diet in combination with daily swimming exercise led to decreased PDK4 expression and
increased muscle glycogen utilization in male rats during exercise relative to a control
diet [51].
Next, the effect of ketone bodies themselves may differ from the effect of keto diets
on muscle glucose metabolism. Namely, it was previously shown that administering a
ketone ester to mice with obesity leads to improved glucose tolerance [
52
]. Although not
connected to exercise, these results are interesting because the same conclusion was drawn

Nutrients 2023,15, 4228 10 of 22
in mice with obesity and a muscle-specific SCOT knockout. This suggests that ketone esters
could exert a beneficial signaling effect on glucose metabolism, which contrasts with the
potential negative effect of keto diets described above. These results were also maintained
in individuals without obesity, where the administration of a ketone supplement prior
to a meal decreased post-prandial glucose levels, which further highlights the potential
signaling effect of exogenous ketones [
53
]. At the same time, ketone intake did not alter
plasma insulin levels or gastric emptying, which suggests that the ketones positively
impacted peripheral glucose uptake. Whether ketones improved peripheral insulin action
or insulin-independent glucose uptake in peripheral tissues requires further investigation.
However, other studies have reported that when exercise is introduced into the study
design, ketone bodies themselves can have a negative effect on glycolysis and insulin
signaling in the muscle. A study that provided male endurance athletes with a beverage
supplemented with an increased number of calories from ketone esters during a bicycle test
found that intramuscular glucose levels were increased at the end of the exercise (relative
to when the participants consumed a beverage higher in carbohydrates) [
7
]. The authors
propose that a state of ketosis leads to decreased muscle glycolysis, which was supported
by decreased levels of fructose-1,6-bisphosphate and 1,3-bisphosphoglycerate (glycolytic
intermediates) in the muscle as a result of the ketone-supplemented beverage (relative
to the carbohydrate beverage). Comparably, in the epitrochlearis muscle of male mice
following a 60 min swimming exercise, ex vivo exposure to 4 mM of D,L-
β
OHB resulted
in increased AS160 phosphorylation after 15 min, but decreased AS160 phosphorylation
after 2 h [
25
], suggesting that short exposure to D,L-
β
OHB increases GLUT4 translocation
but longer exposure decreases it. Further investigations are warranted to determine how a
potential positive effect of exogenous ketones can be exploited. Overall, before providing
recommendations regarding keto diets or supplements for athletes, their impact on glucose
metabolism should be investigated further.
8. Secretion of IL-6 Following a Keto Diet and Exercise Regimen
The muscle can act as an endocrine organ, by producing and releasing small peptides
termed myokines. Myokines can be spontaneously released while at rest, but exercise
(whether acute or chronic) regulates myokine secretion [
54
]. As an example, interleukin
(IL)-6 is a myokine known to be dramatically increased in the circulation in response to
exercise and has also been linked to glucose metabolism in the muscle during exercise [
55
].
Specifically, it was found that IL-6 was increased in response to low glycogen levels in hu-
man muscle [
56
], which led to a postulation that it acts as an energy sensor during exercise
(and by extension, this potential effect may be applicable to a general state of carbohydrate
deprivation) [
55
]. With this in mind, a pair of studies suggest that ketones and exercise may
alter IL-6 levels. In male bodybuilders, an eight-week keto diet (approximately 68% fat,
25% protein and 5% carbohydrates) decreased plasma IL-6, in contrast to a control diet
which increased plasma IL-6. However, plasma levels do not necessarily reflect the quantity
of IL-6 secreted from the muscle since other tissues also secrete this cytokine [
37
]. A second
study measured IL-6 levels specifically in the soleus muscle of male mice administered a
keto diet for eight weeks (76.1% fat, 8.9% protein and 3.5% carbohydrates), with or without
regular exercise, and found that IL-6 mRNA was significantly increased as a result of
exercise, an effect that was enhanced with the keto diet [
8
]. Interestingly, this effect was not
maintained in the gastrocnemius muscle of the same mice, suggesting that the effect of the
keto diet on IL-6 expression may be specific to oxidative muscles. Also, the plasma levels
of IL-6 did not parallel the levels in the muscle: although plasma IL-6 was also increased
with exercise, a control diet enhanced this effect. Overall, the potential connection of IL-6 to
a keto diet in combination with exercise warrants further clarification. Similarly, alterations
in the secretion of other contraction-induced myokines in response to a keto diet should
also be investigated. When doing so, it should be taken into consideration that the high-fat
requirement of keto diets may induce inflammation, which could be the mechanism for
increased production of IL-6 or other myokines tied to an inflammatory response.

Nutrients 2023,15, 4228 11 of 22
9. Muscle TAG Levels Following Exercise and a Keto Diet or Ketone Supplementation
The muscle has lipid droplets which store TAGs, which can be metabolized to generate
fatty acids and ultimately ATP through fatty acid oxidation. These muscle TAG stores
are typically reduced following exercise [
57
], but very few studies have investigated the
impact of ketones and exercise on muscle TAGs, and those that have present conflicting
results. In a group of male cyclists and triathletes who received D-
β
OHB prior to a
stimulated cycling race, intramuscular TAGs were unchanged in a muscle biopsy following
the test [
34
]. However, in male endurance athletes, consuming a beverage with more
calories from ketone esters resulted in a greater decrease in intramuscular lipids following
a fixed-intensity bicycle exercise (relative to consuming a drink higher in carbohydrates) [
7
].
Lastly, in military personnel on a 12-week keto diet (with an unspecified composition)
combined with two weeks of exercise training, intramuscular TAGs increased at the end of
the program, whereas the levels decreased in individuals on a control diet [
30
]. The type
of exercise in this study differs from the others outlined in this section, as the participants
were mainly subjected to regular high-intensity interval training and periodized resistance
and power exercises, rather than an endurance cycling test. Similarly, the participants
followed a keto diet rather than taking ketone supplements. It is thus possible that the
higher muscle TAG content with the keto diet was the result of an increased consumption
of fat rather than increased muscle ketolysis or a signaling effect of the ketones themselves.
Going forward, the possible effect of a keto diet on muscle TAG levels should be taken into
consideration, as a surplus of muscle TAGs has been linked to conditions such as insulin
resistance when the individuals are inactive [58,59].
10. Impact of Ketones on Muscle Health Following Exercise
Finally, a variety of studies have investigated the impact of ketones in combination
with exercise on parameters related to overall muscle health in response to exercise. To
begin with recovery following exercise, a study in male mice found that an eight-week keto
diet (76.1% fat, 8.9% protein and 3.5% carbohydrates) led to an accelerated recovery phase
following a treadmill endurance test (measured by the amount of movement 24 h following
the test) [
60
]. However, another study had a group of recreational athletes perform a series
of eccentric knee extensors following an overnight fast. The participants drank a D-
β
OHB
beverage over the course of the day of the activity and for the two days following it. Muscle
soreness (evaluated subjectively) and muscle function (evaluated by repeating the test)
were not affected by the ketone ester supplementation during the recovery period [
61
].
Similarly, a six-week keto diet (69.5% fat, 20.2% protein and 10.3% carbohydrates) in male
rats leading up to a bout of running on a resistance-loaded running wheel had no effect
on post-exercise muscle protein synthesis [
39
]. Although there are only three studies
investigating the potential impact of ketones on muscle recovery and they had variable
designs and methods for quantifying recovery, it is possible that the type of exercise has an
effect, since no impact on muscle recovery was reported with activities with an increased
eccentric demand (i.e., the knee extensors and resistance running described above).
Some investigations were also made into the effect of a keto diet and exercise on
markers of muscle damage, particularly plasma levels of lactate dehydrogenase (LDH)
and creatine kinase (CK). For example, an eight-week keto diet (76.1% fat, 8.9% protein
and 3.5% carbohydrates) did not protect against increased plasma levels of LDH and CK
72 h following an endurance running test in male mice [
41
], nor did the consumption of
tablets containing
β
OHB prior to a 30 min bout of downhill running in male volunteers [
62
].
Contrarily, in male cyclists who consumed a keto diet (55% fat, 35% protein and 10% carbo-
hydrates) for approximately one week, then a ketone-supplemented tablet prior to a cycling
session, plasma CK and LDH were not increased 120 min post-exercise, as was observed
in the control group [
63
]. It is possible that the difference in the plasma collection time
post-exercise explains the variable results between these studies. Additionally, the type
of exercise may play a role in the effect of a keto diet on muscle damage, as for example,

Nutrients 2023,15, 4228 12 of 22
downhill running has been shown to induce more muscular damage than flat and uphill
running due to increased eccentric contractions [64].
Next, muscle weight following a keto diet was also measured in one study but should
be investigated in more detail in future experiments given the conclusion. Specifically,
in participants with obesity, an eight-week low carbohydrate diet (<50 g per day) with
or without exercise decreased lean muscle mass relative to a control diet [
65
]. Lastly, the
consumption of a ketone supplement beverage had no effect on muscle tissue oxygenation
in male distance runners following a voluntary hypoventilation protocol [
66
], and only
slightly (3%) increased muscle oxygenation in a group of male cyclists who consumed a
ketone ester drink during a 3 h race [
42
]. However, administration of a ketone ester drink
for three weeks, plus regular endurance training in physically active males did improve
several parameters related to muscle angiogenesis [
67
]. The same protocol had previously
been shown to induce a positive effect on exercise performance, suggesting that increased
muscle angiogenesis may be a mechanism for improved exercise performance due to ketone
supplements [32].
Overall, the effect of ketones and exercise on muscle recovery, damage, weight and
oxygenation have not been studied in enough depth to draw conclusions, but they are
parameters that could be taken into consideration going forward.
11. Summary
As outlined above, there is a multitude of variables to consider when analyzing
the effect of ketones and exercise on the muscle. This includes but is not limited to the
muscle type being investigated (e.g., oxidative versus glycolytic), the type of exercise
(e.g., acute versus chronic, aerobic versus resistance), the length and composition of the
keto diet (e.g., medium versus long-chain TAGs, D versus L-
β
OHB) or the comparative
effect of exogenous ketone supplementation. Given the lack of research conducted in
this area and the variability between studies with respect to these parameters, it is often
difficult to draw clear conclusions based on the current literature regarding the relationship
between ketones and exercise in the muscle. Yet, there is evidence to suggest that exercise
increases parameters related to ketone body metabolism (e.g., ketolytic gene expression),
that PDK4 expression increases in response to low muscle glycogen, rather than as a direct
consequence of a keto diet or exercise, and that endurance exercise may spare muscle
glycogen loss due to increased exposure to ketones. It should be noted, however, that
these are only postulations based on the work conducted to date, so future experiments are
needed in order to validate these hypotheses. The effect of ketones and exercise on other
factors, such as exercise performance, myokine secretion and muscle TAG levels, remain
more ambiguous and should be taken into consideration when designing experiments in
the future. The effect of exercise in combination with either ketone supplements or a keto
diet on all the parameters linked to the muscle discussed in this review is summarized in
Figure 1and Table 1.

Nutrients 2023,15, 4228 13 of 22
Nutrients 2023, 15, x FOR PEER REVIEW 13 of 23
glycogen loss due to increased exposure to ketones. It should be noted, however, that
these are only postulations based on the work conducted to date, so future experiments
are needed in order to validate these hypotheses. The effect of ketones and exercise on
other factors, such as exercise performance, myokine secretion and muscle TAG levels,
remain more ambiguous and should be taken into consideration when designing
experiments in the future. The effect of exercise in combination with either ketone
supplements or a keto diet on all the parameters linked to the muscle discussed in this
review is summarized in Figure 1 and Table 1.
Figure 1. Summary of articles investigating the effect of exercise with either ketone supplements or
a keto diet on various parameters in the muscle. Green ↑ = reported an increase or positive effect
relative to control groups, red ↓ = decrease or negative effect, purple X = no effect. The figure was
generated in part by using Servier Medical Art, which is provided by Servier and licensed under a
Figure 1.
Summary of articles investigating the effect of exercise with either ketone supplements or
a keto diet on various parameters in the muscle. Green
↑
= reported an increase or positive effect
relative to control groups, red
↓
= decrease or negative effect, purple X = no effect. The figure was
generated in part by using Servier Medical Art, which is provided by Servier and licensed under a
Creative Commons Attribution 3.0 unported license, as well as rawpixel, which is licensed under a
Creative Commons 1.0 Universal Public Domain Dedication.

Nutrients 2023,15, 4228 14 of 22
Table 1. Summary of the current literature on the effect of ketone bodies and exercise on muscle metabolism.
Reference Study Population Study Design Key Finding(s)
[7] Male endurance athletes
Consumption of ketone ester beverage
during exercise test (2 h bicycle test at
45% VO2max)
Increased muscle D-βOHB levels pre-exercise and 1 h post-exercise
Reduced exercise-induced decrease in muscle glycogen reserve
Increased distance covered in a time trial after 60 min of cycling
Increased intramuscular glucose levels post-exercise
Greater decrease in intramuscular lipids due to exercise
[8] Male mice

8-week keto diet (76.1% fat, 8.9% protein,
3.5% carbohydrates)
8-week exercise regimen
No effect on soleus or gastrocnemius Oxct1 expression
Keto diet alone increased Bdh expression in soleus and decreased Bdh expression in
gastrocnemius
Exercise increased gastrocnemius and soleus Pgc1αexpression
Combination of diet and exercise increased soleus but not gastrocnemius IL-6 mRNA
[11] Male mice
12-week keto diet (88% fat, 11% protein,
1% carbohydrates)
8 weeks treadmill exercise
Keto diet alone decreased gastrocnemius Oxct1 expression, but no additional effect of exercise
Combination of diet and exercise increased gastrocnemius Hmgcs2 expression
Keto diet decreased muscle glycogen and GLUT4 and pyruvate kinase gene expression, which
were all reversed with the exercise regimen
[12] Male rats
8-week keto diet (comparison of
medium and long-chain TAGs)
8-week swimming exercise
Exercise increased epitrochlearis SCOT expression
SCOT expression increased with medium chain relative to long-chain TAGs
Increased PDK4 expression with long but not medium-chain TAGs
Both diets decreased muscle glycogen, which was reversed with exercise only for the
medium-chain diet
[13] Male and female mice Single bout of treadmill running
No effect on quadriceps Bdh,Oxct1 or Acat expression
Increased plasma ketones in female versus male mice
[14] Male rats 10-week swimming exercise Increased gastrocnemius SCOT activity
[15] Male rats 12-week treadmill running
Increased gastrocnemius SCOT, BDH and ACAT activity; and
Increased uptake of acetoacetate and D,L-βOHB in gastrocnemius
[16] Male rats 15-week treadmill running
Decreased SCOT activity in diaphragm
No effect on SCOT activity in intercostal muscle
[17] Male rats 14–28 weeks treadmill running
Increased uptake of acetoacetate and βOHB together in perfused hindlimb muscle
No effect on uptake of βOHB alone
[18] Male rats Single bout of treadmill running No effect on acetoacetate or βOHB-supported respiration in permeabilized gastrocnemius
[19] C2C12 cells Exposure to forskolin to mimic exercise Increased βOHB in cell lysates and culture media

Nutrients 2023,15, 4228 15 of 22
Table 1. Cont.
Reference Study Population Study Design Key Finding(s)
[22] Male mice
4-week keto diet (unspecified
composition)
Single exhaustive treadmill and weight
bearing swimming test
Increased gastrocnemius Pdk4 expression
No change in running distance or time, or in swimming time
[23] Male mice
6-week high fat keto diet (83.9% fat,
16.1% protein, 0% carbohydrates)
3 weeks treadmill running
Increased quadriceps Pdk4 expression due to keto diet
No additional effect of exercise and no effect on PDH activity or pyruvate oxidation
Training increased glycogen levels independently of exercise
Increased phosphorylation of AMPK in the quadriceps
Increased Pgc1αexpression
[24]
Participants performing >6
weekly hours of endurance
exercise
10-day keto diet (80% fat, 15% protein
and 5% carbohydrates) or D-βOHB
supplementation
Keto diet increased vastus lateralis PDK4 expression
No effect of supplements on PDK4

Keto diet decreased performance on incremental cycling test (90 min at 70% VO
2
max, followed
by incremental increases to fatigue), but supplements had no effect
Keto diet, but not ketone supplements, increased plasma insulin and glucose levels following
glucose tolerance test
[25]Epitrochlearis from male
mice
Muscle harvested after swimming for
60 min
2 h incubation with 4 mM D,L-βOHB
No impact on PDH phosphorylation at Ser293
Increased glycogen levels
Decreased AMPK and ACC phosphorylation after 15 min, but no difference after 2 h
AS160 phosphorylation increased after 15 min, but decreased after 2 h
[26]Gastrocnemius from male
mice
6-week keto diet (69.5% fat, 20.2%
protein and 10.3% carbohydrates)
6 weeks on resistance running wheel
No effect on Pdk4 expression
Increased Pgc1αexpression due to exercise
Exercise increased muscle Glut4 gene expression
[29] Male endurance runners Low carbohydrate diet (>60% fat, <20%
carbohydrates) for >6 months

No difference in muscle glycogen following an endurance running test and 2 h recovery period
[30] Military personnel 12-week keto (unspecified composition)
2-week mixed training program
Decreased muscle glycogen
Increased intramuscular TAGs
[31] Male athletes
Overnight fast and interval cycling
exercise
Consumption of D-βOHB beverage
Muscle glycogen was replenished more rapidly
[32] Physically active males
3-week endurance and interval training
Regular consumption of ketone ester
drink
Maintenance of muscle glycogen following 30 min time trial
Increased power output in the final 30 min of a 2 h endurance activity

Nutrients 2023,15, 4228 16 of 22
Table 1. Cont.
Reference Study Population Study Design Key Finding(s)
[33] Physically active males Glycogen depleting exercise in the leg,
then consumption of ketone ester drink
No change in muscle glycogen after 5 h recovery period
Decreased muscle AMPK phosphorylation 90 min post-exercise, but no difference after 5 h
[34] Male cyclists Consumption of D-βOHB before and
during a 3 h race
No change in muscle glycogen after the exercise
No effect in power output during the race
No effect on intramuscular TAGs
[35] Male participants 3-day keto diet (50% fat, 45% protein
and 5% carbohydrates)
Keto diet decreased mean power output in two 30 s exercise bike tests
[36] Female participants 4-week keto diet (77% fat, 19% protein
and 4% carbohydrates)

Keto diet decreased time to exhaustion on ingle incremental cycling test (increase of 30 W every
4 min until 120 W)
[37] Male bodybuilders 
8-week keto diet (approximately 68% fat,
25% protein and 5% carbohydrates)
No effect on performance on bench press and squat tests
Decreased plasma IL-6
[38]Male and female
participants
8-week cyclical keto diet (keto diet on
weekdays, high carbohydrate diet on
weekends) with regular strength and
aerobic workouts
Increased performance on certain strength exercises
[39] Male rats 6-week keto diet (69.5% fat, 20.2%
protein and 10.3% carbohydrates)
No effect on running distance on a voluntary running wheel throughout the 6 weeks
No effect on phosphorylation of AMPK in gastrocnemius
No effect on post-exercise muscle protein synthesis
[40] Female mice 8 h fast to induce ketosis No effect on endurance in treadmill running test
[41] Male rats 
8-week keto diet (76.1% fat, 8.9% protein
and 3.5% carbohydrates)
Longer running time in male rats during an exhaustive running test
Did not protect against increased plasma levels of LDH and CK 72 h post endurance running
[42] Male cyclists Administration of ketone ester drink
during stimulated cycling race
No impact on power output during the race
Increased muscle oxygenation during the race
[43] Male mice 
6 weeks of D,L-
β
OHB supplementation

Increased distance, time to exhaustion and maximal speed on a weekly treadmill test only after
2 weeks
[44] Male SCOT knockout mice Time to exhaustion treadmill test No difference in running time and distance
[48] Male cyclists
Low carbohydrate, high fat diet
(variable compositions) for at least
6 months
Decreased muscle GLUT4 and IRS1
[51] Male rats 
4-week high carbohydrate, fat-restricted
diet and daily swimming exercise
Decreased PDK4 expression and increased muscle glycogen utilization

Nutrients 2023,15, 4228 17 of 22
Table 1. Cont.
Reference Study Population Study Design Key Finding(s)
[60] Male mice 
8-week keto diet (76.1% fat, 8.9% protein
and 3.5% carbohydrates)
Accelerated recovery phase following a treadmill endurance test
[61] Recreational athletes
Participants performed eccentric knee
extensors following overnight fast
Also consumed a D-βOHB beverage on
the day of the activity, and for the 2 days
after
Did not affect muscle soreness and muscle function during the recovery period
[62] Male participants Consumption of βOHB tablets prior to
30 min of downhill running
No effect on plasma LDH and CK post-exercise
[63] Male cyclists
Keto diet (55% fat, 35% protein and 10%
carbohydrates) for 1 week, and ketone
supplemented tablet prior to cycling
session
No effect on plasma LDH or CK 120 min post-exercise
[65] Participants with obesity 8-week low carbohydrate diet (<50 g
per day) with regular exercise
Keto diet decreased lean muscle mass
[66] Male distance runners
Consumption of ketone supplemented
beverage
Voluntary hypoventilation protocol
No effect on muscle tissue oxygenation
[67] Physically active males Ketone ester drink and regular
endurance training for 3 weeks
Improved parameters related to muscle angiogenesis

Nutrients 2023,15, 4228 18 of 22
12. Limitations and Future Direction
A major limitation of this review is the overall lack of research studies that investigate
the connection between muscle, exercise and ketones. Many studies investigate two of these
factors, but few cover all three. This issue is further compounded by the high variability
in the design of studies pertinent to the goal of this review. Additional limitations and
recommendations for future studies are outlined below.
Firstly, it should be noted that the high-fat requirement of a keto diet may lead to
negative consequences in the muscle that are not due to increased ketone exposure in
itself (e.g., inflammatory responses). Future experiments which further investigate the
mechanisms for effects connected to a keto diet would assist in making this distinction. To
this point, continuing to explore the difference between keto diets and exogenous ketone
supplementation may be advantageous, because supplements eliminate the need for high
levels of dietary fat. As mentioned in the section on the effect of keto diets on glucose
metabolism, it is also possible that the low carbohydrate requirement of a keto diet is
negatively impacting GLUT4. Future studies could employ a high carbohydrate diet as a
control group to better elucidate the impact of carbohydrate deprivation on the muscle.
Going forward, separate study groups should be implemented to clearly investigate
the effect of a keto diet or exogenous ketone supplementation alone, exercise alone and a
combination of both variables. This will allow for clearer determinations into their effect
on the muscle, as many studies published to date do not make these distinctions (for
example, they only use participants who are physically active). Hence, clinical studies
should also make use of individuals who are sedentary, as the effect of ketones may be
variable in individuals without a significant background in physical activity. Increasing the
diversity of study designs and the associated participant profiles is necessary to obtain a
more comprehensive understanding of the relationship between ketone bodies and exercise
in the muscle.
Similarly, female participants or animals should be used more frequently, and con-
trasted to male subject groups, as almost all the research presented here used exclusively
male subjects/rodents. It is crucial that research in this area becomes more inclusive, as the
effect of increased ketolysis may be variable between biological sexes, and recommenda-
tions regarding keto diets and supplements may be vastly different for males and females.
In general, before recommendations are made regarding keto diets or exogenous
ketone supplementation, the long-term impact of these regimens on muscle metabolism,
particularly glucose oxidation, should be determined.
13. Conclusions
Overall, as summarized above, there is evidence to suggest that increased exposure
to ketones can influence (whether positively or negatively) muscle metabolism, but a
significant number of important questions pertaining to this area of research remain out-
standing. As the popularity of keto diets and ketone supplements continues to rise, an
increasing number of individuals are augmenting their exposure to ketone bodies through
their diet, athletes may be implementing the regimens into their training programs and
doctors are recommending these interventions to their patients. However, until more work
is conducted on the relationship between ketones, the muscle and exercise, it is uncertain
whether these recommendations and lifestyle alterations are beneficial or detrimental. As
such, future investigations into the connection between exercise and keto diets or exoge-
nous ketone supplementation is strongly encouraged, especially as they relate to skeletal
muscle metabolism.

Nutrients 2023,15, 4228 19 of 22
Author Contributions:
Conceptualization, H.K. and C.A.; Writing—Original Draft Preparation, H.K.;
Writing—Review and Editing, J.R.U. and C.A.; Supervision, C.A.; Funding Acquisition, J.R.U. and
C.A. All authors have read and agreed to the published version of the manuscript.
Funding:
This research was funded by The Canadian Institutes of Health Research (CIHR), Project
Grant number 173515. J.R.U. is a Tier 2 Canada Research Chair (Pharmacotherapy of Energy
Metabolism in Obesity). This project was also supported by a CIHR Canada Graduate Scholar-
ship Doctoral Award (FBD-187636) and a Master’s scholarship provided by the Institut du Savoir
Montfort, both to H.K.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: No new data were created in this review article.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Puchalska, P.; Crawford, P.A. Multi-Dimensional Roles of Ketone Bodies in Fuel Metabolism, Signaling, and Therapeutics. Cell
Metab. 2017,25, 262–284. [CrossRef] [PubMed]
2.
Robinson, A.M.; Williamson, D.H. Physiological Roles of Ketone Bodies as Substrates and Signals in Mammalian Tissues. Physiol.
Rev. 1980,60, 143–187. [CrossRef] [PubMed]
3.
Puchalska, P.; Nelson, A.B.; Stagg, D.B.; Crawford, P.A. Determination of Ketone Bodies in Biological Samples via Rapid
UPLC-MS/MS. Talanta 2021,225, 122048. [CrossRef] [PubMed]
4.
Webber, R.J.; Edmond, J. Utilization of L(+)-3-Hydroxybutyrate, D(-)-3-Hydroxybutyrate, Acetoacetate, and Glucose for Respira-
tion and Lipid Synthesis in the 18-Day-Old Rat. J. Biol. Chem. 1977,252, 5222–5226. [CrossRef] [PubMed]
5.
Batch, J.T.; Lamsal, S.P.; Adkins, M.; Sultan, S.; Ramirez, M.N. Advantages and Disadvantages of the Ketogenic Diet: A Review
Article. Cureus 2020,12, e9639. [CrossRef]
6.
Stubbs, B.J.; Cox, P.J.; Evans, R.D.; Santer, P.; Miller, J.J.; Faull, O.K.; Magor-Elliott, S.; Hiyama, S.; Stirling, M.; Clarke, K. On the
Metabolism of Exogenous Ketones in Humans. Front. Physiol. 2017,8, 848. [CrossRef]
7.
Cox, P.J.; Kirk, T.; Ashmore, T.; Willerton, K.; Evans, R.; Smith, A.; Murray, A.J.; Stubbs, B.; West, J.; McLure, S.W.; et al. Nutritional
Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metab. 2016,24, 256–268. [CrossRef]
8.
Ma, S.; Huang, Q.; Tominaga, T.; Liu, C.; Suzuki, K. An 8-Week Ketogenic Diet Alternated Interleukin-6, Ketolytic and Lipolytic
Gene Expression, and Enhanced Exercise Capacity in Mice. Nutrients 2018,10, 1696. [CrossRef]
9.
DeFronzo, R.A.; Tripathy, D. Skeletal Muscle Insulin Resistance Is the Primary Defect in Type 2 Diabetes. Diabetes Care
2009
,32
(Suppl. 2), S157–S163. [CrossRef]
10.
Frontera, W.R.; Ochala, J. Skeletal Muscle: A Brief Review of Structure and Function. Calcif. Tissue Int.
2015
,96, 183–195.
[CrossRef]
11.
Shimizu, K.; Saito, H.; Sumi, K.; Sakamoto, Y.; Tachi, Y.; Iida, K. Short-Term and Long-Term Ketogenic Diet Therapy and the
Addition of Exercise Have Differential Impacts on Metabolic Gene Expression in the Mouse Energy-Consuming Organs Heart
and Skeletal Muscle. Nutr. Res. 2018,60, 77–86. [CrossRef] [PubMed]
12.
Fukazawa, A.; Koike, A.; Karasawa, T.; Tsutsui, M.; Kondo, S.; Terada, S. Effects of a Ketogenic Diet Containing Medium-Chain
Triglycerides and Endurance Training on Metabolic Enzyme Adaptations in Rat Skeletal Muscle. Nutrients
2020
,12, 1269.
[CrossRef] [PubMed]
13. Holcomb, L.E.; Rowe, P.; O’Neill, C.C.; DeWitt, E.A.; Kolwicz, S.C. Sex Differences in Endurance Exercise Capacity and Skeletal
Muscle Lipid Metabolism in Mice. Physiol. Rep. 2022,10, e15174. [CrossRef] [PubMed]
14.
El Midaoui, A.; Chiasson, J.L.; Tancrède, G.; Nadeau, A. Physical Training Reverses Defect in 3-Ketoacid CoA-Transferase Activity
in Skeletal Muscle of Diabetic Rats. Am. J. Physiol. Endocrinol. Metab. 2005,288, E748–E752. [CrossRef] [PubMed]
15.
Winder, W.W.; Baldwin, K.M.; Holloszy, J.O. Exercise-Induced Increase in the Capacity of Rat Skeletal Muscle to Oxidize Ketones.
Can. J. Physiol. Pharmacol. 1975,53, 86–91. [CrossRef]
16.
Green, H.J.; Reichmann, H. Differential Response of Enzyme Activities in Rat Diaphragm and Intercostal Muscles to Exercise
Training. J. Neurol. Sci. 1988,84, 157–165. [CrossRef]
17.
Ohmori, H.; Kawai, K.; Yamashita, K. Enhanced Ketone Body Uptake by Perfused Skeletal Muscle in Trained Rats. Endocrinol.
Jpn. 1990,37, 421–429. [CrossRef]
18.
Petrick, H.L.; Brunetta, H.S.; Pignanelli, C.; Nunes, E.A.; van Loon, L.J.C.; Burr, J.F.; Holloway, G.P. In Vitro Ketone-Supported
Mitochondrial Respiration Is Minimal When Other Substrates Are Readily Available in Cardiac and Skeletal Muscle. J. Physiol.
2020,598, 4869–4885. [CrossRef]
19.
Kwak, S.E.; Bae, J.H.; Lee, J.H.; Shin, H.E.; Zhang, D.; Cho, S.C.; Song, W. Effects of Exercise-Induced Beta-Hydroxybutyrate on
Muscle Function and Cognitive Function. Physiol. Rep. 2021,9, e14497. [CrossRef]

Nutrients 2023,15, 4228 20 of 22
20.
Pilegaard, H.; Neufer, P.D. Transcriptional Regulation of Pyruvate Dehydrogenase Kinase 4 in Skeletal Muscle during and after
Exercise. Proc. Nutr. Soc. 2004,63, 221–226. [CrossRef]
21.
Boyle, K.E.; Canham, J.P.; Consitt, L.A.; Zheng, D.; Koves, T.R.; Gavin, T.P.; Holbert, D.; Neufer, P.D.; Ilkayeva, O.; Muoio, D.M.; et al.
A High-Fat Diet Elicits Differential Responses in Genes Coordinating Oxidative Metabolism in Skeletal Muscle of Lean and Obese
Individuals. J. Clin. Endocrinol. Metab. 2011,96, 775–781. [CrossRef] [PubMed]
22.
Zhang, J.; Chen, B.; Zou, K. Effect of Ketogenic Diet on Exercise Tolerance and Transcriptome of Gastrocnemius in Mice. Open Life
Sci. 2023,18, 20220570. [CrossRef] [PubMed]
23.
Huang, T.-Y.; Linden, M.A.; Fuller, S.E.; Goldsmith, F.R.; Simon, J.; Batdorf, H.M.; Scott, M.C.; Essajee, N.M.; Brown, J.M.;
Noland, R.C. Combined Effects of a Ketogenic Diet and Exercise Training Alter Mitochondrial and Peroxisomal Substrate
Oxidative Capacity in Skeletal Muscle. Am. J. Physiol. Endocrinol. Metab. 2021,320, E1053–E1067. [CrossRef] [PubMed]
24.
Dearlove, D.J.; Soto Mota, A.; Hauton, D.; Pinnick, K.; Evans, R.; Miller, J.; Fischer, R.; Mccullagh, J.S.O.; Hodson, L.; Clarke, K.; et al.
The Effects of Endogenously- and Exogenously-Induced Hyperketonemia on Exercise Performance and Adaptation. Physiol. Rep.
2022,10, e15309. [CrossRef]
25.
Takahashi, Y.; Terada, S.; Banjo, M.; Seike, K.; Nakano, S.; Hatta, H. Effects of
β
-Hydroxybutyrate Treatment on Glycogen
Repletion and Its Related Signaling Cascades in Epitrochlearis Muscle during 120 Min of Postexercise Recovery. Appl. Physiol.
Nutr. Metab. 2019,44, 1311–1319. [CrossRef]
26.
Hyatt, H.W.; Kephart, W.C.; Holland, A.M.; Mumford, P.; Mobley, C.B.; Lowery, R.P.; Roberts, M.D.; Wilson, J.M.; Kavazis, A.N.
A Ketogenic Diet in Rodents Elicits Improved Mitochondrial Adaptations in Response to Resistance Exercise Training Compared
to an Isocaloric Western Diet. Front. Physiol. 2016,7, 533. [CrossRef]
27.
Vigh-Larsen, J.F.; Ørtenblad, N.; Spriet, L.L.; Overgaard, K.; Mohr, M. Muscle Glycogen Metabolism and High-Intensity Exercise
Performance: A Narrative Review. Sports Med. 2021,51, 1855–1874. [CrossRef]
28.
Browning, J.D.; Baxter, J.; Satapati, S.; Burgess, S.C. The Effect of Short-Term Fasting on Liver and Skeletal Muscle Lipid, Glucose,
and Energy Metabolism in Healthy Women and Men. J. Lipid Res. 2012,53, 577–586. [CrossRef]
29.
Volek, J.S.; Freidenreich, D.J.; Saenz, C.; Kunces, L.J.; Creighton, B.C.; Bartley, J.M.; Davitt, P.M.; Munoz, C.X.;
Anderson, J.M.
;
Maresh, C.M.; et al. Metabolic Characteristics of Keto-Adapted Ultra-Endurance Runners. Metabolism
2016
,65, 100–110. [CrossRef]
30.
Miller, V.J.; LaFountain, R.A.; Barnhart, E.; Sapper, T.S.; Short, J.; Arnold, W.D.; Hyde, P.N.; Crabtree, C.D.; Kackley, M.L.;
Kraemer, W.J.; et al. A Ketogenic Diet Combined with Exercise Alters Mitochondrial Function in Human Skeletal Muscle While
Improving Metabolic Health. Am. J. Physiol. Endocrinol. Metab. 2020,319, E995–E1007. [CrossRef]
31.
Holdsworth, D.A.; Cox, P.J.; Kirk, T.; Stradling, H.; Impey, S.G.; Clarke, K. A Ketone Ester Drink Increases Postexercise Muscle
Glycogen Synthesis in Humans. Med. Sci. Sports Exerc. 2017,49, 1789–1795. [CrossRef] [PubMed]
32.
Poffé, C.; Ramaekers, M.; Van Thienen, R.; Hespel, P. Ketone Ester Supplementation Blunts Overreaching Symptoms during
Endurance Training Overload. J. Physiol. 2019,597, 3009–3027. [CrossRef] [PubMed]
33.
Vandoorne, T.; De Smet, S.; Ramaekers, M.; Van Thienen, R.; De Bock, K.; Clarke, K.; Hespel, P. Intake of a Ketone Ester Drink
during Recovery from Exercise Promotes MTORC1 Signaling but Not Glycogen Resynthesis in Human Muscle. Front. Physiol.
2017,8, 310. [CrossRef] [PubMed]
34.
Poffé, C.; Ramaekers, M.; Bogaerts, S.; Hespel, P. Exogenous Ketosis Impacts Neither Performance nor Muscle Glycogen
Breakdown in Prolonged Endurance Exercise. J. Appl. Physiol. 2020,128, 1643–1653. [CrossRef]
35.
Langfort, J.; Zarzeczny, R.; Pilis, W.; Nazar, K.; Kaciuba-U´scitko, H. The Effect of a Low-Carbohydrate Diet on Performance,
Hormonal and Metabolic Responses to a 30-s Bout of Supramaximal Exercise. Eur. J. Appl. Physiol. Occup. Physiol.
1997
,76,
128–133. [CrossRef]
36.
Sjödin, A.; Hellström, F.; Sehlstedt, E.; Svensson, M.; Burén, J. Effects of a Ketogenic Diet on Muscle Fatigue in Healthy, Young,
Normal-Weight Women: A Randomized Controlled Feeding Trial. Nutrients 2020,12, 955. [CrossRef]
37.
Paoli, A.; Cenci, L.; Pompei, P.; Sahin, N.; Bianco, A.; Neri, M.; Caprio, M.; Moro, T. Effects of Two Months of Very Low
Carbohydrate Ketogenic Diet on Body Composition, Muscle Strength, Muscle Area, and Blood Parameters in Competitive
Natural Body Builders. Nutrients 2021,13, 374. [CrossRef]
38.
Kysel, P.; Haluzíková, D.; Doležalová, R.P.; La ˇnková, I.; Lacinová, Z.; Kasperová, B.J.; Trnovská, J.; Hrádková, V.; Mráz, M.;
Vilikus, Z.; et al. The Influence of Cyclical Ketogenic Reduction Diet vs. Nutritionally Balanced Reduction Diet on Body
Composition, Strength, and Endurance Performance in Healthy Young Males: A Randomized Controlled Trial. Nutrients
2020
,
12, 2832. [CrossRef]
39.
Roberts, M.D.; Holland, A.M.; Kephart, W.C.; Mobley, C.B.; Mumford, P.W.; Lowery, R.P.; Fox, C.D.; McCloskey, A.E.; Shake, J.J.;
Mesquita, P.; et al. A Putative Low-Carbohydrate Ketogenic Diet Elicits Mild Nutritional Ketosis but Does Not Impair the Acute
or Chronic Hypertrophic Responses to Resistance Exercise in Rodents. J. Appl. Physiol. 2016,120, 1173–1185. [CrossRef]
40.
Holcomb, L.E.; O’Neill, C.C.; DeWitt, E.A.; Kolwicz, S.C. The Effects of Fasting or Ketogenic Diet on Endurance Exercise
Performance and Metabolism in Female Mice. Metabolites 2021,11, 397. [CrossRef]
41.
Ma, S.; Huang, Q.; Yada, K.; Liu, C.; Suzuki, K. An 8-Week Ketogenic Low Carbohydrate, High Fat Diet Enhanced Exhaustive
Exercise Capacity in Mice. Nutrients 2018,10, 673. [CrossRef] [PubMed]

Nutrients 2023,15, 4228 21 of 22
42.
Poffé, C.; Robberechts, R.; Podlogar, T.; Kusters, M.; Debevec, T.; Hespel, P. Exogenous Ketosis Increases Blood and Muscle
Oxygenation but Not Performance during Exercise in Hypoxia. Am. J. Physiol. Regul. Integr. Comp. Physiol.
2021
,321, R844–R857.
[CrossRef] [PubMed]
43.
Monsalves-Alvarez, M.; Morales, P.E.; Castro-Sepulveda, M.; Sepulveda, C.; Rodriguez, J.M.; Chiong, M.; Eisner, V.;
Lavandero, S.
;
Troncoso, R.
β
-Hydroxybutyrate Increases Exercise Capacity Associated with Changes in Mitochondrial Function in Skeletal
Muscle. Nutrients 2020,12, 1930. [CrossRef]
44.
Mechchate, H.; Abdualkader, A.M.; Bernacchi, J.B.; Gopal, K.; Tabatabaei Dakhili, S.A.; Yang, K.; Greenwell, A.A.; Kong, X.;
Crawford, P.A.; Al Batran, R. Defective Muscle Ketone Body Oxidation Disrupts BCAA Catabolism by Altering Mitochondrial
Branched-Chain Aminotransferase. Am. J. Physiol. Endocrinol. Metab. 2023,324, E425–E436. [CrossRef]
45.
Xie, Z.; Zhang, D.; Chung, D.; Tang, Z.; Huang, H.; Dai, L.; Qi, S.; Li, J.; Colak, G.; Chen, Y.; et al. Metabolic Regulation of Gene
Expression by Histone Lysine β-Hydroxybutyrylation. Mol. Cell 2016,62, 194–206. [CrossRef]
46.
Richter, E.A.; Ruderman, N.B. AMPK and the Biochemistry of Exercise: Implications for Human Health and Disease. Biochem. J.
2009,418, 261–275. [CrossRef] [PubMed]
47.
Liang, H.; Ward, W.F. PGC-1alpha: A Key Regulator of Energy Metabolism. Adv. Physiol. Educ.
2006
,30, 145–151. [CrossRef]
[PubMed]
48. Webster, C.C.; van Boom, K.M.; Armino, N.; Larmuth, K.; Noakes, T.D.; Smith, J.A.; Kohn, T.A. Reduced Glucose Tolerance and
Skeletal Muscle GLUT4 and IRS1 Content in Cyclists Habituated to a Long-Term Low-Carbohydrate, High-Fat Diet. Int. J. Sport.
Nutr. Exerc. Metab. 2020,30, 210–217. [CrossRef]
49.
Tremblay, F.; Lavigne, C.; Jacques, H.; Marette, A. Defective Insulin-Induced GLUT4 Translocation in Skeletal Muscle of High
Fat-Fed Rats Is Associated with Alterations in both Akt/Protein Kinase B and Atypical Protein Kinase C (Zeta/Lambda) Activities.
Diabetes 2001,50, 1901–1910. [CrossRef]
50.
Kahn, B.B.; Pedersen, O. Suppression of GLUT4 Expression in Skeletal Muscle of Rats That Are Obese from High Fat Feeding but
Not from High Carbohydrate Feeding or Genetic Obesity. Endocrinology 1993,132, 13–22. [CrossRef]
51.
Karasawa, T.; Kondo, S.; Fukazawa, A.; Koike, A.; Tsutsui, M.; Terada, S. Effects of Dietary Fat Restriction on Endurance
Training-Induced Metabolic Adaptations in Rat Skeletal Muscle. J. Oleo Sci. 2021,70, 253–262. [CrossRef] [PubMed]
52.
Tabatabaei Dakhili, S.A.; Yang, K.; Locatelli, C.A.A.; Saed, C.T.; Greenwell, A.A.; Chan, J.S.F.; Chahade, J.J.; Scharff, J.;
Al Imarah, S.
;
Eaton, F.; et al. Ketone Ester Administration Improves Glycemia in Obese Mice. Am. J. Physiol. Cell Physiol.
2023
,325, C750–C757.
[CrossRef] [PubMed]
53.
Greaves, G.; Xiang, R.; Rafiei, H.; Malas, A.; Little, J.P. Prior Ingestion of a Ketone Monoester Supplement Reduces Postprandial
Glycemic Responses in Young Healthy-Weight Individuals. Appl. Physiol. Nutr. Metab. 2021,46, 309–317. [CrossRef] [PubMed]
54.
Garneau, L.; Aguer, C. Role of Myokines in the Development of Skeletal Muscle Insulin Resistance and Related Metabolic Defects
in Type 2 Diabetes. Diabetes Metab. 2019,45, 505–516. [CrossRef]
55.
Docherty, S.; Harley, R.; McAuley, J.J.; Crowe, L.A.N.; Pedret, C.; Kirwan, P.D.; Siebert, S.; Millar, N.L. The Effect of Exercise on
Cytokines: Implications for Musculoskeletal Health: A Narrative Review. BMC Sports Sci. Med. Rehabil. 2022,14, 5. [CrossRef]
56.
Keller, C.; Steensberg, A.; Pilegaard, H.; Osada, T.; Saltin, B.; Pedersen, B.K.; Neufer, P.D. Transcriptional Activation of the IL-6
Gene in Human Contracting Skeletal Muscle: Influence of Muscle Glycogen Content. FASEB J. 2001,15, 2748–2750. [CrossRef]
57.
Watt, M.J.; Cheng, Y. Triglyceride Metabolism in Exercising Muscle. Biochim. Biophys. Acta Mol. Cell Biol. Lipids
2017
,1862,
1250–1259. [CrossRef]
58.
Kelley, D.E.; Goodpaster, B.H. Skeletal Muscle Triglyceride. An Aspect of Regional Adiposity and Insulin Resistance. Diabetes
Care 2001,24, 933–941. [CrossRef] [PubMed]
59.
Goodpaster, B.H.; He, J.; Watkins, S.; Kelley, D.E. Skeletal Muscle Lipid Content and Insulin Resistance: Evidence for a Paradox in
Endurance-Trained Athletes. J. Clin. Endocrinol. Metab. 2001,86, 5755–5761. [CrossRef]
60.
Huang, Q.; Ma, S.; Tominaga, T.; Suzuki, K.; Liu, C. An 8-Week, Low Carbohydrate, High Fat, Ketogenic Diet Enhanced Exhaustive
Exercise Capacity in Mice Part 2: Effect on Fatigue Recovery, Post-Exercise Biomarkers and Anti-Oxidation Capacity. Nutrients
2018,10, 1339. [CrossRef]
61.
Jameson, T.S.O.; Islam, H.; Wall, B.T.; Little, J.P.; Stephens, F.B. Oral Ketone Monoester Supplementation Does Not Accelerate
Recovery of Muscle Force or Modulate Circulating Cytokine Concentrations after Muscle-Damaging Eccentric Exercise in Healthy
Males and Females. Exp. Physiol. 2022,107, 1339–1348. [CrossRef] [PubMed]
62.
Nunan, D.; Howatson, G.; van Someren, K.A. Exercise-Induced Muscle Damage Is Not Attenuated by Beta-Hydroxy-Beta-
Methylbutyrate and Alpha-Ketoisocaproic Acid Supplementation. J. Strength. Cond. Res.
2010
,24, 531–537. [CrossRef] [PubMed]
63.
Lima, R.C.P.; Camerino, S.R.A.S.; França, T.C.L.; Rodrigues, D.S.A.; Gouveia, M.G.S.; Ximenes-da-Silva, A.; Bassini, A.;
Prado, E.S.
;
Cameron, L.C. Keto Analogues and Amino Acids Supplementation Induces a Decrease of White Blood Cell Counts and a
Reduction of Muscle Damage during Intense Exercise under Thermoneutral Conditions. Food Funct.
2017
,8, 1519–1525.
[CrossRef]
64.
Park, K.-S.; Lee, M.-G. Effects of Unaccustomed Downhill Running on Muscle Damage, Oxidative Stress, and Leukocyte
Apoptosis. J. Exerc. Nutrition Biochem. 2015,19, 55–63. [CrossRef]
65.
Perissiou, M.; Borkoles, E.; Kobayashi, K.; Polman, R. The Effect of an 8 Week Prescribed Exercise and Low-Carbohydrate Diet on
Cardiorespiratory Fitness, Body Composition and Cardiometabolic Risk Factors in Obese Individuals: A Randomised Controlled
Trial. Nutrients 2020,12, 482. [CrossRef] [PubMed]

Nutrients 2023,15, 4228 22 of 22
66.
Prins, P.J.; Buxton, J.D.; McClure, T.S.; D’Agostino, D.P.; Ault, D.L.; Welton, G.L.; Jones, D.W.; Atwell, A.D.; Slack, M.A.; Slack, M.L.; et al.
Ketone Bodies Impact on Hypoxic CO2 Retention Protocol During Exercise. Front. Physiol. 2021,12, 780755. [CrossRef]
67.
Poffé, C.; Robberechts, R.; Van Thienen, R.; Hespel, P. Exogenous Ketosis Elevates Circulating Erythropoietin and Stimulates
Muscular Angiogenesis During Endurance Training Overload. J. Physiol. 2023,601, 2345–2358. [CrossRef]
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