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Re-Examining High-Fat Diets for Sports Performance: Did We Call the 'Nail in the Coffin' Too Soon?

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During the period 1985-2005, studies examined the proposal that adaptation to a low-carbohydrate (<25 % energy), high-fat (>60 % energy) diet (LCHF) to increase muscle fat utilization during exercise could enhance performance in trained individuals by reducing reliance on muscle glycogen. As little as 5 days of training with LCHF retools the muscle to enhance fat-burning capacity with robust changes that persist despite acute strategies to restore carbohydrate availability (e.g., glycogen supercompensation, carbohydrate intake during exercise). Furthermore, a 2- to 3-week exposure to minimal carbohydrate (<20 g/day) intake achieves adaptation to high blood ketone concentrations. However, the failure to detect clear performance benefits during endurance/ultra-endurance protocols, combined with evidence of impaired performance of high-intensity exercise via a down-regulation of carbohydrate metabolism led this author to dismiss the use of such fat-adaptation strategies by competitive athletes in conventional sports. Recent re-emergence of interest in LCHF diets, coupled with anecdotes of improved performance by sportspeople who follow them, has created a need to re-examine the potential benefits of this eating style. Unfortunately, the absence of new data prevents a different conclusion from being made. Notwithstanding the outcomes of future research, there is a need for better recognition of current sports nutrition guidelines that promote an individualized and periodized approach to fuel availability during training, allowing the athlete to prepare for competition performance with metabolic flexibility and optimal utilization of all muscle substrates. Nevertheless, there may be a few scenarios where LCHF diets are of benefit, or at least are not detrimental, for sports performance.
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REVIEW ARTICLE
Re-Examining High-Fat Diets for Sports Performance: Did We
Call the ‘Nail in the Coffin’ Too Soon?
Louise M. Burke
1,2
Published online: 9 November 2015
The Author(s) 2015. This article is published with open access at Springerlink.com
Abstract During the period 1985–2005, studies examined
the proposal that adaptation to a low-carbohydrate (\25 %
energy), high-fat ([60 % energy) diet (LCHF) to increase
muscle fat utilization during exercise could enhance perfor-
mance in trained individuals by reducing reliance on muscle
glycogen. As little as 5 days of training with LCHF retools the
muscle to enhance fat-burning capacity with robust changes
that persist despite acute strategies to restore carbohydrate
availability (e.g., glycogen supercompensation, carbohydrate
intake during exercise). Furthermore, a 2- to 3-week exposure
to minimal carbohydrate (\20 g/day) intake achieves adap-
tation to high blood ketone concentrations. However, the
failure to detect clear performance benefits during endurance/
ultra-endurance protocols, combined with evidence of
impaired performance of high-intensity exercise via a down-
regulation of carbohydrate metabolism led this author to dis-
miss the use of such fat-adaptation strategies by competitive
athletes in conventional sports. Recent re-emergence of
interest in LCHF diets, coupled with anecdotes of improved
performance by sportspeople who follow them, has created a
need to re-examine the potential benefits of this eating style.
Unfortunately, the absence of new data prevents a different
conclusion from being made. Notwithstanding the outcomes
of future research, there is a need for better recognition of
current sports nutrition guidelines that promote an individu-
alized and periodized approach to fuel availability during
training, allowing the athlete to prepare for competition
performance with metabolic flexibility and optimal utilization
of all muscle substrates. Nevertheless, there may be a few
scenarios where LCHF diets are of benefit, or at least are not
detrimental, for sports performance.
Key Points
The current interest in low carbohydrate high fat
(LCHF) diets for sports performance is based on
enthusiastic claims and testimonials rather than a
strong evidence base. Although adaptation to a
LCHF (whether ketogenic or not) increases the
muscle’s capacity to utilize fat as an exercise
substrate, there is no proof that this leads to a clear
performance advantage. In fact, there is a risk of
impairing the capacity for high intensity exercise.
The current guidelines for carbohydrate intake in the
athlete’s training diet appear to be poorly
understood. Sports nutrition experts do not promote a
‘high carbohydrate diet’’ for all athletes. Rather, the
evolving model is that athletes should follow an
individualized approach, whereby carbohydrate
intake is periodized throughout the training cycle
according to the fuel needs of each workout, the
importance of performing well in the session and/or
the potential to amplify the adaptive response to
exercise via exposure to low carbohydrate
availability. There is a need for ongoing research and
practice to identify a range of approaches to optimal
training and competition diets according to the
specific requirements of an event and the experience
of the individual athlete.
&Louise M. Burke
louise.burke@ausport.gov.au
1
Sports Nutrition, Australian Institute of Sport, Canberra,
ACT, Australia
2
Mary MacKillop Institute for Health Research, Australian
Catholic University, Melbourne, VIC, Australia
123
Sports Med (2015) 45 (Suppl 1):S33–S49
DOI 10.1007/s40279-015-0393-9
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1 Introduction
In 2006, after *15 years of failed attempts to harness
adaptations to a high-fat diet as an ergogenic strategy for
sports performance in well-trained competitors, this author
and a colleague were invited to contribute a commentary
on the publication of a new study from the University of
Cape Town [1]. After careful inspection of the paper, we
speculated on its role as ‘the nail in the coffin’ of fat
adaptation for athletic performance [2]. We wrote about
what is now known as low-carbohydrate, high-fat (LCHF)
diets, ‘it seems that we are near to closing the door on
one application of this dietary protocol. Scientists may
remain interested in the body’s response to different dietary
stimuli, and may hunt for the mechanisms that underpin the
observed changes in metabolism and function. However,
those at the coal face of sports nutrition can delete ‘fat
loading’ and high-fat diets from their list of genuine
ergogenic aids for endurance and ultra-endurance sports—
at least for the conventional events within these categories’
[2].
A decade later, theories and claims that fat adaptation
can enhance sports performance have strongly re-emerged
from several sources via peer-reviewed literature [36], lay
publications [7], and a highly developed information net-
work that did not exist during the previous incarnation of
this dietary theory: social media [8,9]. Because of the
number and fervor of the discussions and the rapidity/reach
of the information spread among both scientific and athletic
circles, there is a need to re-examine the proposal that an
LCHF diet enhances sports performance in competitive
athletes. This review summarizes the theory and the evi-
dence to support LCHF diets for athletic performance. It
reviews experimental data that informed the conclusions
made by this author in 2006 and the context of competitive
sport to which they were applied. It then frames the current
claims made for the LCHF diet and athletic performance
against the current sports nutrition guidelines and any
additional evidence against which they should be judged.
Finally, it provides a judgement about whether there is
justification to recommend the LCHF diet for athletic
performance, overall or in specific scenarios, and the
research that should be undertaken to continue to evolve
the guidelines for the optimal training/competition diet. To
provide objectivity in discussing the current promotion of
the LCHF diet for enhanced sports performance, quotes
from key proponents taken from both peer-reviewed liter-
ature and less formal sources are presented. While the
inclusion of the latter sources in a scientific review may be
considered unconventional, it is now recognized that many
scientists actively use social media to promote their views
[10] and even conduct research [11], albeit involving non-
traditional methodologies. Therefore, it provides an
important source of information for constructing the theo-
ries that need to be examined. In addition, although the
examination of current evidence is primarily based on peer-
reviewed literature involving well-controlled scientific tri-
als in trained individuals [12], consideration will be given
to anecdotal accounts provided via lay sources to guide
future research efforts or identify scenarios in which LCHF
diets appear to have utility.
2 Sports Performance: A Brief Overview of Fuel
Systems
Although it is beyond the scope of this review to ade-
quately summarize the determinants of effective training
and optimal competition performances, several general
comments related to fueling strategies for training and
competition are provided to add context to discussions in
this review. Sporting events last from seconds (e.g., jumps,
throws) to weeks (e.g., Tour de France cycling stage race),
with success being determined by a complex and often
changing range of characteristics, including power,
strength, endurance, agility, skill, and decision making.
The role of training is to accumulate adaptations in the
muscle and other body organs/systems to achieve specific
characteristics that underpin success in the athlete’s event
via a series of systematic and periodized stimuli involving
the interaction of nutrition and exercise [13]. Fueling
strategies during this period should also be periodized [14]
according to the demands of the session and the relative
priorities of training with high intensity/quality, practicing
competition nutrition and promoting the adaptive response
to the training stimulus (see Table 1). In the competition
phase, the key role for nutrition is to address the specific
limiting factors that would otherwise cause fatigue or a
decrement in performance [15]. In many sporting events,
the capacity of body fuel stores to support optimal function
of the muscle and central nervous system (CNS) is one
such factor.
In the muscle, exercise is fueled by an intricate system
that integrates the production of adenosine triphosphate
(ATP) from a combination of intra- and extra-cellular
substrates via pathways that are oxygen dependent (oxi-
dation of fat and carbohydrate) and independent (phos-
phocreatine system and anaerobic glycolysis). The relative
contribution of various substrates to the fuel mix depends
on various factors, including the mode, intensity, and
duration of exercise, the athlete’s training status, and both
recent and longer-term dietary intake [16]. For optimal
competition performance, the athlete needs a combination
of adequate fuel stores in relation to the demands of his or
S34 L. M. Burke
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Table 1 Summary of current knowledge and guidelines for optimizing fuel needs for training and competition nutrition
Issue Current knowledge and guidelines
CHO intake in the training
diet
Previous focus on ‘high-CHO diets’ should be replaced by consideration of ‘CHO availability’, in which the daily amount and timing of CHO intake is compared
with muscle fuel cost of training: ‘high CHO availability’ =intake providing adequate fuel for training needs, while ‘low CHO availability’ =intake is likely to
be associated with CHO depletion [53]
Daily CHO intake should not be static but should be periodized across training microcycles and macrocycles according to fuel cost of training load and the
importance of training with high CHO availability [53]
When workouts involve high-intensity/volume/quality/technique, the day’s eating patterns should provide high CHO availability [53]
When workouts involve exercise of lower intensity/quality, it is less important to follow patterns that achieve high CHO availability [53]
Deliberately manipulating diet/training to exercise with low CHO availability can enhance the adaptive response to the training stimulus, and may be periodized
into the training program according to individual goals and experience [14,59]
Issue Strategy Targeted event(s) Current knowledge and guidelines
Optimizing
competition
performance by
increasing fuel
availability
(especially to
addressing the
scenario of limited
fuel availability)
Increasing muscle phosphocreatine stores
to enhance recovery during period
between repeated high-intensity intervals:
creatine loading
Stop and go sports: e.g., team sports, racket sports Likely to be effective in sports/positions in which gradual depletion
of phosphocreatine stores is limiting to movement patterns [62]
Recommended protocol [63]:
Rapid loading: 5 days @ 20 g/day creatine in split doses
Slow loading: 30 days @ 3 g/day
Maintenance: 3 g/day
Increasing muscle glycogen stores in
day(s) prior to event: CHO loading
Prolonged sustained or intermittent sports
(usually [90 min) in which muscle glycogen
stores become depleted: e.g., marathon, cycling
road races, mid-field positions in some team games
Likely to be effective if event would otherwise deplete muscle
glycogen stores, leading to reduction in speed and distance
covered [64]
Recommended protocol [53]: 36–48 h @ 10–12 g/kg/day
CHO ?taper
Increase in muscle/liver glycogen in hours
prior to event: pre-event meal
Prolonged sustained or intermittent sports
(usually [45 min), especially where pre-exercise
muscle/liver glycogen are not optimized by other
strategies
Likely to be effective if intake increases CHO availability (increase
in liver/muscle glycogen [increase in rate of CHO oxidation
during exercise) especially in CHO-limited event [53,65]
Recommended protocol [53]: 1–4 g/kg CHO at 1–4 h pre-event
Increase in exogenous supply of CHO:
intake of CHO just prior to and during
event
Not needed for metabolic effects in events
of more than *75 min, but may be useful
for central effects in events greater than
*45 min
Prolonged sustained or intermittent sports
(usually [75 min) in which additional fuel source
can replace/spare otherwise limited muscle
glycogen stores: e.g., marathon, cycling road
races, triathlons, team and racket sports
Likely to be effective if intake provides a readily available CHO
supply to the muscle, particularly if muscle glycogen becomes
depleted. May also address CNS impairment in events or
individuals in which reductions in blood glucose concentrations
occur [24,66]
Recommended protocol [53]: 1–2.5 h: 30–60 g/h CHO, [2.5–3 h:
up to 90 g/h CHO
Sustained high-intensity sports (45–75 min) not
typically considered to be limited by muscle
glycogen stores, e.g., cycling time trial, half
marathon
Likely to be effective in enhancing pacing strategy via effect on
‘reward centers’ in brain [61,67]
Recommended protocol [53]: frequent exposure of mouth and oral
cavity to CHO, including mouth rinse
High-Fat Diets and Sports Performance S35
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her event as well as ‘metabolic flexibility’, hereby defined
in the context of sports performance as the ability to rapidly
and efficiently utilize these pathways to maximize ATP
regeneration. Although we lack specific data on the meta-
bolic pathways and substrate use in the majority of com-
petitive sports, technological advances such as the
development of power meters and global positioning sys-
tem units have allowed the collection of information such
as power output, heart rate, and movement patterns that
indirectly capture the metabolic demands of some events.
A key understanding from such data is that the fuel
demands of many sports are complex and often misun-
derstood. An example of particular relevance to this review
is that sports such as multi-stage road cycling, triathlons,
and marathons are classified as endurance and ultra-en-
durance events conducted at sub-maximal exercise inten-
sities; in fact, for competitive athletes at least, the terrain,
pacing strategies, and tactical elements in these events
mean that brief but critical parts of the race that often
determine the outcomes (e.g., breakaways, hill climbs,
surges, sprint finishes) are conducted at higher and often
near maximal pace [1719]. In addition, for such athletes,
even the ‘background’ pace from which these brief spurts
are performed in endurance sports such as the marathon
requires high exercise economy and a sustained use of very
high percentage of maximal aerobic intensity [20]. The
fueling of the brain and CNS also needs to be considered,
since motor recruitment, perception of effort, pacing
strategies, and the execution of skills and decision making
are also important in determining performance. Here, the
main substrates are blood glucose and glycogen stored in
the astrocytes [21,22], although under certain conditions
where blood concentrations of ketone bodies are high, they
may provide an additional fuel source [23].
Competition nutrition strategies that can enhance fuel
availability are summarized in Table 1and include strate-
gies that attempt to directly increase the size of a limited
muscle store (e.g., loading with creatine or carbohydrate)
as well as others that attempt to spare the use of the limited
store by providing an alternative substrate. For events
greater than *1 h duration, the focus is on tactics that
increase carbohydrate availability for the muscle and brain,
since low carbohydrate availability is associated with
fatigue via a number of peripheral and central mechanisms
[24]. Body fat stores—comprising intramuscular triglyc-
eride (IMTG), blood lipids, and adipose tissue IMTG—
represent a relatively abundant fuel substrate even in the
leanest of athletes. Although endurance training is known
to enhance an athlete’s capacity for fat oxidation during
exercise [16], a large body of research over the past 3
decades has been dedicated to exploring ways in which this
can be further up-regulated to enhance exercise capacity
and sports performance by reducing the reliance on the
Table 1 continued
Issue Strategy Targeted event(s) Current knowledge and guidelines
Increase in fatty acid availability: fasting or
short-term (1–3 days) high-fat diet
Prolonged sustained or intermittent sports
(usually [75 min) in which additional fuel source
can replace/spare otherwise limited muscle
glycogen stores: e.g., marathon, cycling road
races, triathlon, team and racket sports
Typically unable to increase (and may even impair) exercise
capacity/performance since enhanced fat oxidation is unable to
compensate for low muscle glycogen stores
Protocol: not recommended [25,26]
Increase in fatty
acid availability:
high-fat pre-event
meal (?heparin)
or intralipid
infusion
No clear performance benefit despite
increased fat oxidation. Use of intralipid
infusions and heparin to ensure high fatty
acid availability is not practical
Protocol: not recommended [25,26]
Increase in fatty
acid availability:
feeding of
medium chain
triglycerides
during exercise
Typically unable to increase (and may even
impair) exercise capacity/performance
since the large amounts needed to impact
fuel metabolism cause gut problems [68]
Protocol: not recommended [25,26]
CHO carbohydrate, CNS central nervous system
S36 L. M. Burke
123
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muscle’s limited glycogen stores and/or the need to con-
sume carbohydrate during the event. As summarized in
Table 2and in several reviews [25,26], acute tactics to
increase free fatty availability by increasing fat intake in
the hours or days prior to exercise, or consuming fat during
exercise have proved unsuccessful or impractical. There-
fore, attention has shifted to chronic tactics that could re-
tool the muscle to make better use of fat as an exercise fuel.
3 Chronic Adaptation to High-Fat Diets: Research
from 1980 to 2006
In contrast to short-term exposure to an LCHF diet, which
reduces exercise capacity by depleting liver and muscle
stores of glycogen without producing a compensatory
increase in fat oxidation [27,28], longer-term adherence to
this dietary regimen causes a range of adaptations to
enhance the breakdown, transport, and oxidation of fat in
skeletal muscle [29]. Several different approaches have
been investigated.
3.1 Ketogenic High-Fat Diets
According to recent reviews [5,6], historical observations
of considerable exercise stamina in explorers who followed
traditional Inuit diets almost devoid of carbohydrate (en-
ergy contribution: 85 % fat, 15 % protein) led to a labo-
ratory investigation of this phenomenon in the 1980s [30,
31]. In this study by Dr. Stephen Phinney, carefully con-
ducted in a metabolic ward, five well-trained cyclists were
tested following 1 week of a carbohydrate-rich diet
(*57 % of energy) and again following 28 days of a
severely carbohydrate-restricted (\20 g/day) but isoener-
getic diet with energy contributions of 85 % fat and 15 %
protein (Table 2). This diet was associated with ketosis, as
demonstrated by increased blood concentrations of beta-
hydroxybutyrate from \0.05 to [1 mmol/L after a week,
and this was maintained thereafter. Exercise was monitored
by a time to exhaustion cycling test at *63 % of maximal
aerobic capacity (VO
2
max) under conditions of low car-
bohydrate availability (overnight fast and water intake
during the ride) [30], with the mean result being a main-
tenance of exercise capacity (see Fig. 1). Despite the
negligible intake of carbohydrate, resting muscle glycogen
stores were not depleted but rather reduced to *45 % of
values seen on the high-carbohydrate phase (76 vs.
140 mmol/kg wet weight muscle). Furthermore, in both
trials, at the cessation of exercise, muscle glycogen
depletion was seen in type 1 fibers with a fourfold reduc-
tion in its contribution to fuel use in the LCHF trial. Blood
glucose contribution to fuel use was reduced threefold,
with gluconeogenic contributions from glycerol released
from triglyceride use as well as lactate, pyruvate, and
certain amino acids preventing hypoglycemia during
exercise as well as allowing glycogen storage between
training sessions. Lipid oxidation was increased to make up
the fuel substrate for the exercise task.
The researchers’ insights into the results of their study
were that ‘‘metabolic adaptation to limit CHO [carbohy-
drate] oxidation can facilitate moderate submaximal exer-
cise during ketosis to the point that it becomes comparable
to that observed after a high CHO diet.’’ Furthermore, they
noted that ‘‘because muscle glycogen stores require many
days for repletion, whereas even very lean individuals
maintain appreciable caloric stores as fat, there is potential
benefit in this keto-adapted state for athletes participating
in prolonged endurance exercise over two or more days’’.
However, they also commented on the results of VO
2
max
tests undertaken during each dietary phase with respect to
the ketogenic diet: ‘the price paid for the conservation
of CHO during exercise appears to be a limitation of the
intensity of exercise that can be performed there was a
marked attenuation of respiratory quotient [RQ] value at
VO
2
max suggesting a severe restriction on the ability of
subjects to do anaerobic work’’. Their explanation for this
observation was that ‘‘the controlling factor does not
appear to be the presence or absence of substrate in the
fiber. Rather it is more likely a restriction on substrate
mobilization or fiber recruitment. The result, in any case, is
a throttling of function near VO
2
max’’.
The researchers were clear that their ketogenic diet did
not, as is popularly believed, enhance exercise capacity/
performance, noting that, at best, endurance at sub-maxi-
mal intensities was preserved at the expense of ability to
undertake high-intensity exercise. However, examination
of the design and outcomes call for further caution.
Although excellent dietary control was achieved in this
study, few details were provided of the training protocols
followed by the cyclists. It is curious in light of the order
effect in the study design (all subjects undertook the
ketogenic exercise trial 4 weeks after their carbohydrate
trial), that no benefit to exercise capacity was derived from
an additional training period. Furthermore, it should be
recognized that the exercise task was undertaken under
conditions that should have favored any advantage to being
adapted to low carbohydrate availability (moderate-inten-
sity exercise, overnight fast, no intake of carbohydrate
during exercise). However, and most importantly, the focus
on the mean outcomes of the trial in a small sample size
hides the experiences of the individual cyclists. As shown
in Fig. 1, the published interpretations of the results of this
study are largely skewed by the experience of a single
subject who showed a large enhancement of exercise
capacity after the ketogenic diet (and additional training
period). Indeed, statistical analysis of the same data using a
High-Fat Diets and Sports Performance S37
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Table 2 Summary of studies of adaptation to ketogenic low-carbohydrate, high-fat diet on performance of trained individuals
Athletes and study design LCHF adaptation protocol Performance protocol Nutritional status/
strategies for
performance
Performance advantage with LCHF
Pre 2006
Well-trained cyclists [30]
(n=5M)
Crossover design with order effect
(control diet first)
7 days
HC (57 % CHO) then 28 days LCHF
(fat =85 % E, CHO =\20 g/day)
Cycling; TTE at 60 % VO
2
max Overnight-
fasted ?no CHO
intake during
exercise
No
NS difference in TTE between trials (151
vs. 147 min for LCHF and HC). Group
data skewed by one participant who
increased time to fatigue by 156 % on
LCHF trial (Fig. 1)
Post 2006
Moderately trained off-road
cyclists [49](n=8M)
Crossover design
28 days
HC (CHO =50 % E)
LCHF (fat =70 % E, CHO =15 %)?
truly ketogenic
Cycling; VO
2
max test Not stated No
Mixed results, with small increase in
VO
2
max (56 vs. 59.2 ml/kg/min for HC
and LCHF, p\0.01) but reduction in
maximum workload (350 vs. 362 W,
p=0.037). Small favorable change in
body composition with LCHF (loss
of *1.8 kg with body fat loss from
14.9 to 11.0 % BM, p\0.01)
Elite artistic gymnasts [50]
(n=8M)
Crossover design with order effect
(control diet second)
30 days
HC (CHO =47 % E, 3.9 g/kg) then 30
days LCHF (fat =55 % E,
CHO \25 g/day) (note protein =40 %
E?added supplements)
Strength exercises: squat jump,
countermovement jump, push-ups,
reverse grip chin test, legs closed barrier
maximum test
Not stated No
No change in strength measurements
across either dietary phase—therefore,
no impairment of performance measures
with LCHF diet. Small favorable
change in body composition with LCHF
(loss of *1.5 kg with body fat loss
from 7.6 to 5.4 % BM)
BM body mass, CHO carbohydrate, Eenergy, HC high-carbohydrate diet, LCHF low-carbohydrate high-fat diet, Mmale, NS not significant, TTE time to exhaustion, VO
2
max maximal oxygen
uptake
S38 L. M. Burke
123
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magnitude-based inferences approach [32] reveals an
unclear outcome, with the chances of a substantially pos-
itive, trivial, and substantially negative outcome being 32,
32, and 36 %, respectively (Stellingwerff, personal
communication).
3.2 Non-Ketogenic High-Fat Diets
A number of studies have been undertaken in trained
individuals involving exposure for C7 days to a diet high
in fat and restricted in carbohydrate content without
achieving ketosis [3337]; much of this work was driven
by Dr. Vicki Lambert and Professor Tim Noakes from the
University of Cape Town. Two studies in which carbohy-
drate and fat intake was manipulated in trained populations
have not been included in this summary since the dietary
changes were not sufficient to meet the criteria of [60 %
fat intake or \25 % carbohydrate intake [38,39]. The
summarized literature (Table 3) includes one study that
focused on titrating the carbohydrate content of the diet in
modestly trained female cyclists [33] and four studies that
specifically set out to adapt their subjects to a high-fat diet
[3437], although in one case, the smaller degree of car-
bohydrate restriction resulted in a failure to create clear
differences in muscle glycogen content between treatments
[37]. Again, the diets provided within studies were isoen-
ergetic and aimed at maintaining energy balance.
In the case of studies specifically focused on adapting
athletes to a high fat intake, the rationale of increasing
dietary fat involved increasing IMTG stores [37], restrict-
ing carbohydrate to reduce muscle glycogen content [34
36] and allowing sufficient exposure for adaptations to
occur to retool the muscle to alter fuel utilization patterns
during exercise to compensate for altered fuel availability
[3437]. The avoidance of ketosis was chosen to remove its
confounding effect on the relationship between respiratory
exchange ratio and substrate utilization during exercise,
thereby preventing a true measurement of changes in car-
bohydrate and fat oxidation during exercise [34]. A range
of adaptive responses to the LCHF diet was observed or
confirmed in the trained individuals.
As summarized in Table 3, the effect of exposure to the
LCHF diets on exercise capacity/performance was tested
under a range of different exercise scenarios and feeding
strategies. This includes a series of exercise protocols
undertaken sequentially [34] or within a single exercise
task [36], as well as dietary strategies that would either
further increase fat availability [33,36,37], increase car-
bohydrate availability [3537], or deliberately decrease
carbohydrate availability against current guidelines or
common practices [34]. In some cases, different dietary
strategies were implemented before and during the exercise
protocols for the high carbohydrate and LCHF trials,
making it difficult to isolate the effects of the fat adaptation
per se [36,37]. This variability in study design makes it
difficult to make a single and all-encompassing assessment
of the effect of LCHF on exercise, as is popularly desired.
Theoretically, however, it offers the opportunity to identify
conditions under which adaptation to a high-fat diet may be
of benefit or harm to sports performance. Unfortunately,
the small number of studies and the small sample sizes in
the available literature do not allow this opportunity to be
fully exploited. The learnings from these studies have been
incorporated into the summary at the end of this section. In
the meantime, attention is drawn to two important obser-
vations from this body of literature:
1. Evidence of reduced utilization of muscle glycogen as
an exercise fuel following adaptation to LCHF cannot
be considered true glycogen ‘sparing’ since the
observations are confounded by lower resting glyco-
gen concentrations, which are known to reduce
glycogen use per se [40]. Only scenarios in which
muscle glycogen concentrations are matched prior to
exercise can allow the specific effect of fat adaptation
on muscle glycogen utilization as an exercise fuel to be
measured.
2. The period required for adaptation to the non-keto-
genic LCHF is shorter than previously considered.
According to the time course study of Goedecke et al.
[35], whereby muscle fuel utilization was tracked after
5, 10, and 15 days of exposure to the LCHF diet, a
substantial shift to increase fat oxidation and reduce
carbohydrate utilization was achieved by 5 days
| | | | | | | | | | |
40 80 120 160 200
Time (min)
High CHO
Low CHO High Fat
147 + 13
151 + 25
Fig. 1 Exercise capacity (time to exhaustion at 62–64 % maximal
aerobic capacity, equivalent to *185 W after 7 days of high-
carbohydrate diet followed by 28 days of low-carbohydrate high-fat
diet. Data represent mean ±standard error of the mean from five
well-trained cyclists (not significantly different), with individual data
points represented by O. Redrawn from Phinney et al. [30]CHO
carbohydrate
High-Fat Diets and Sports Performance S39
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Table 3 Effect of up to 28 days of adaptation to high-fat low carbohydrate diet on performance of trained individuals
Athletes LCHF adaptation protocol Performance protocol Nutritional status/strategies for
performance
Performance advantage with LCHF
Moderately trained cyclists
[33](n=7F)
Crossover design
7 days
LCHF (fat =59 % E,
CHO =1.2 g/kg BM)
HC (CHO =6.4 g/kg BM)
Cycling
TTE at 80 % VO
2
max
3–4 h after meal, no CHO intake
during exercise
No
In fact, performance deteriorated with LCHF.
Time to exhaustion reduced by 47 % on
LCHF trial
Well-trained cyclists [34]
(n=5M)
Crossover design
14 days
LCHF (fat =67 % E,
CHO =17 % E
a
)
HC (CHO =74 % E
a
)
Cycling
30 s Wingate test ?TTE at 90 %
VO
2
max ?TTE at 60 % VO
2
max
Overnight-fasted ?no CHO intake
during exercise
No: two higher intensity tests
Yes: Submaximal cycling
Time to exhaustion increased by 87 % on
LCHF trial commenced with lower
glycogen stores due to preceding exercise
Well-trained cyclists [35]
(n=16 M)
Parallel-group design
15 days
LCHF (fat =69 %E,
CHO =2.2 g/kg BM)
HC (CHO =5.5 g/kg BM)
Cycling
150 min at 70 % VO
2
max ?40 km TT
Performance measured at t=0, 5, 10, and
15 days
MCT intake 1.5 h before event
(*14 g)
MCT (0.3 g/kg/h) and CHO (0.8 g/
kg/h) during exercise
No
TT performance increased over time in both
groups as a result of training protocol.
Significant improvements seen in both
groups by day 10, but no difference in mean
improvement between groups. Important
finding of study: adaptations achieved after
only 5 days of high-fat diet
Well-trained cyclists [36]
(n=7M)
Crossover design
14 days
LCHF (fat =66 % E,
CHO =*2.4 g/kg)
HC (CHO =*8.6 g/kg,
70 % CHO)
Cycling
5 h including 15 min TT ?100 km TT
LCHF =high-fat pre-event meal
HC =high CHO pre-event meal
Both: 0.8 g/kg/h CHO during ride
Yes: submaximal intensity exercise
No: higher-intensity exercise
Relative to baseline: HC showed small NS
decreases in performance of both 15 min
TT and 100 km TT
LCHF showed larger but NS decrease in
performance of 15 min TT but small NS
improvement in 100 km TT
Well-trained duathletes
[37](n=11 M)
Crossover design
5 weeks
LCHF (fat =53 % E,
CHO =*3.6 g/kg)
HC (CHO =*6.9 g/kg,
68 % CHO)
Cycling
40 min incremental protocol ?20 min TT
@*89 % VO
2
max
Running (separate day)
Outdoor 21 km TT
LCHF =high-fat pre-event meal
HC =high CHO pre-event meal
Intake pre and during half marathon
not stated
No
Self-selected work output similar for cycling
TT in both dietary treatments (298 ±6 vs.
297 ±7 W, NS) for LCHF and HC,
respectively. Half marathon time not
different between trials (80 min
12 s ±86 s vs. 80 min 24 s ±82 s, NS)
BM body mass, CHO carbohydrate, Eenergy Ffemale, HC high-carbohydrate diet, LCHF low-carbohydrate high-fat diet, Mmale, MCT medium chain triglyceride, NS not significant, TT time
trial, TTE time to exhaustion, VO
2
max maximal oxygen uptake
a
g/kg intakes unavailable
S40 L. M. Burke
123
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without further enhancement thereafter. Of course, it
should be noted that a shift in respiratory exchange
ratio during exercise, marking shifts in substrate
utilization can reflect the prevailing availability of
substrate rather than a true adaptation in the muscle.
However, other studies have confirmed the presence of a
robust change in the muscle’s substrate use via observa-
tions of alterations in the concentrations or activity of
proteins or metabolites that regulate fatty acid availability,
as well as the persistence of increased fat oxidation in the
face of abundant carbohydrate supplies. Such evidence is
discussed later.
Importantly, the observation from this series of stud-
ies—that retooling of already trained muscle to optimize
muscle utilization of fat as an exercise fuel can be achieved
in a conveniently short period—led in part to the next
phase of investigation, in which attempts were made to
enhance sports performance by separately optimizing the
muscle’s capacity for lipid and carbohydrate utilization.
3.3 Fat Adaptation and Carbohydrate Restoration
In the absence of finding clear benefits from adapting to a
high-fat diet on exercise performance, attention was drawn
to a tactic of dietary periodization in which a short-term
adaptation to an LCHF diet might be followed by glycogen
restoration (‘carbohydrate loading’) with 1–3 days of a
carbohydrate-rich diet with [1,36,4144] or without [45]
additional carbohydrate intake pre- and during subsequent
exercise. Such strategies were aimed at promoting simul-
taneous increases in fat and carbohydrate availability and
utilization during exercise. Indeed, studies that directly
compared fuel utilization during submaximal exercise
under controlled conditions after the fat adaptation protocol
and then again after carbohydrate restoration practices [41,
42,45] showed that the muscle re-tooling was robust
enough to maintain an increase in fat utilization during
exercise in the face of the practices that supported plentiful
carbohydrate availability (Fig. 2).
As discussed in the previous section, a range of per-
mutation and combinations of dietary strategies and exer-
cise protocols can be investigated in combination with the
fat adaptation and carbohydrate restoration strategies to test
the effect of such dietary periodization on exercise
capacity/performance. The available literature is summa-
rized in Table 4and includes multiple studies from the
author’s own laboratory as well as from the University of
Cape Town. However, within this group of investigations,
only one fully published study [1] attempted to investigate
an exercise test that bears any real resemblance to a
sporting competition; its characteristics include a sole
focus on performance rather than a hybrid of metabolism
and performance, self-pacing, and a protocol interspersing
passages of high-intensity exercise against a background of
moderate-intensity work to reflect the stochastic profile of
many real-life events. This study [1], which prompted the
2006 editorial about which this review revolves, merits
special reflection before a general summary of the literature
is provided.
Havemann et al. [1] had well-trained cyclists undertake
either a 6-day LCHF diet followed by a 1-day high-
0
10
20
30
40
50
60
70
Day
1
Day
6
20 40 60 80 100 120
Day 7
0
50
100
150
200
250
300
350
HCHO + CHO FAT-adapt + CHO
HCHO - CHO FAT-adapt - CHO
CHO oxidation (umol/kg/min) Fat oxidation (umol/kg/min)
a
b
Fig. 2 Effect of 5 days of adaptation to a low-carbohydrate high-fat
diet and 1 day of a high-carbohydrate diet to restore muscle glycogen
(FAT-adapt) on rate of carbohydrate oxidation (a) and rate of fat
oxidation (b) during cycling at 70 % maximal aerobic capacity
compared with control trial (6 days of a high-carbohydrate diet). Data
are taken from two studies in which no additional carbohydrate was
consumed on the day of a 120-min cycling bout at this same workload
(-carbohydrate) [45] or where carbohydrate was consumed before
and throughout the 120-min cycling task (?carbohydrate) [41].
Values are mean ±SEM for eight well-trained cyclists at day 1
(baseline), day 6 (after 5 days of low-carbohydrate high-fat diet or
5 days of high-carbohydrate diet) and during 120 min of steady-state
cycling on day 7 (following 1 day of high-carbohydrate diet). The
adaptation to 5 days of high-fat diet increased fat utilization and
reduced carbohydrate utilization during submaximal exercise, per-
sisting despite the restoration of muscle glycogen on day 6 or the
intake of additional carbohydrate before/during exercise on day 7.
Reproduced from Burke et al. [41] with permission. CHO carbohy-
drate, HCHO high carbohydrate
High-Fat Diets and Sports Performance S41
123
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Table 4 Effect of adaptation (5–10 days) to high-fat low-carbohydrate diet followed by carbohydrate restoration in trained individuals
Participant
characteristics
LCHF adaptation protocol CHO restoration Performance protocol Nutritional status/strategies for
performance
Performance advantage with LCHF
adaptation ?CHO restoration
Well-trained
cyclists/triathletes
[45](n=8M)
Crossover design
5 days
LCHF-adapt (fat =68 % E;
CHO =18 % E, 2.5 g/kg BM) or
HC (CHO =74 % E, 9.6 g/kg BM
CHO)
1 day
rest ?high
CHO
(CHO =75 %
E, 10 g/kg
BM)
Cycling
120 min at 70 %
VO
2
max ?*30 min
TT (time to complete
7 J/kg BM)
Fasted ?no CHO intake during
exercise
Perhaps for individuals
Two participants performed badly on HC
trial, probably because of
hypoglycemia. Plasma glucose better
maintained on LCHF-adapt trial. TT not
significantly different between trials:
30.73 ±1.12 vs. 34.17 ±2.62 min for
LCHF and HC trial. However, mean
difference in TT =8 % enhancement
with LCHF trial (p=0.21, NS; 95 %
CI –6 to 21).
Well-trained
cyclists and
triathletes [41]
(n=8M)
Crossover design
5 days
LCHF-adapt (fat =68 % E;
CHO =18 % E, 2.5 g/kg BM) or
HC (CHO =70 % E, 9.3 g/kg BM
CHO)
1 day
rest ?high
CHO
(CHO =75 %
E, 10 g/kg
BM)
Cycling
120 min at 70 %
VO
2
max ?*30 min
TT (time to complete
7 J/kg BM)
CHO intake 2 h before exercise
(2 g/kg BM) and during exercise
(0.8 g/kg/h)
No
Plasma glucose maintained in both trials
due to CHO intake during exercise.
Difference in TT between trials was
trivial: LCHF-
adapt =25.53 ±0.67 min;
HC =25.45 ±0.96 min (p=0.86,
NS). Mean difference in TT =0.7 %
impairment with LCHF-adapt trial
(95 % CI –1.7 to 0.4)
Highly-trained
cyclists and
triathletes [42]
(n=7M)
Crossover design
6 days
LCHF-adapt (fat =69 % E
CHO =16 % E, 2.5 g/kg BM) or
HC (CHO =75 % E, 11 g/kg BM)
1 day
rest ?high
CHO
(CHO =75 %
E, 11 g/kg
BM)
Cycling
240 min at 65 %
VO
2
max ?60 min TT
(distance in 1 h)
CHO intake before exercise (3 g/
kg BM) and during exercise
(1.3 g/kg/h)
No or perhaps for individuals
TT performance NS between trials:
44.25 ±0.9 vs. 42.1 ±1.2 km for
LCHF-adapt and HC trial. However,
mean difference in TT
performance =4 % enhancement with
LCHF-adapt (p=0.11, NS) (95 % CI –
3 to 11)
Highly-trained
cyclists and
triathletes [43]
(n=7M)
Crossover design
5 days
LCHF-adapt (fat =69 % E
CHO =16 % E, 2.5 g/kg BM) or
HC (CHO =75 % E, 11 g/kg BM)
1 day
rest ?high
CHO
(CHO =75 %
E, 11 g/kg
BM)
Cycling
240 min at 65 %
VO
2
max ?60 min TT
(distance in 1 h)
CHO intake before exercise (3 g/
kg BM) and during exercise
(1.3 g/kg/h)
No
Additional six subjects undertaken to test
for Type 1 error in previous study [42].
TT performance NS between trials:
42.92 ±1.46 vs. 42.94 ±1.41 km for
LCHF-adapt and HC trial (p=0.98).
Performance difference =0.02 km or
0.1 %
S42 L. M. Burke
123
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Table 4 continued
Participant
characteristics
LCHF adaptation protocol CHO restoration Performance protocol Nutritional status/strategies for
performance
Performance advantage with LCHF
adaptation ?CHO restoration
Trained cyclists and
triathletes [44]
(n=5M)
Crossover design
10 days
LCHF-adapt (fat =65 % E,
CHO =15 % E, 1.6 g/kg BM) or
HC (CHO =53 % E, 5.8 g/kg BM)
3 days high
CHO
(CHO =65 %
E, 7 g/kg
BM) ?1 day
rest
Cycling
150-min cycling at 70 %
VO
2
max ?20-km
(*30 min) TT
MCT intake 1 h before event
(*14 g); MCT (0.3 g/kg/h) and
CHO (0.8 g/kg/h) during
exercise
Yes
Difference in TT performance =4%
enhancement with LCHF-adapt:
29.35 ±1.25 vs. 30.68 ±1.55 min for
LCHF-adapt and HC (p\0.05)
Well-trained
cyclists [36]
(n=7M)
Crossover design
11.5 days
LCHF-adapt (*2.4 g/kg, 15 % CHO;
66 % fat) or HC (CHO =*8.6 g/
kg, 70 % E)
2.5 days high
CHO (6.8 g/
kg BM)
Cycling
5-h protocol including
15-min TT ?100-km
TT
HC: High-CHO pre-event meal
Both: 0.8 g/kg/h CHO during
exercise
Perhaps—submaximal intensity exercise
No—higher-intensity exercise
Relative to baseline testing: HC trial
showed small NS decrease in
performance of both 15-min TT and
100-km TT. LCHF-adapt showed no
change in 15-min TT but small NS
enhancement of 100-km TT
Well-trained
cyclists [1]
(n=8M)
Crossover design
6 days
LCHF-adapt (fat =68 % E
CHO =17 % E, 1.8 g/kg BM) or
HC (CHO =68 % E, 7.5 g/kg BM)
1 day
rest ?high
CHO (8–10 g/
kg)
Cycling
100 km TT, including
494-km
sprints ?591-km
sprints
CHO consumed during ride No—in fact, performance enhancement of
1-km sprints
Differences between 100-km TT
performances: NS (156 min 54 s vs.
153 min 10 s for LCHF-adapt vs. HC).
Difference between power output
during 4-km sprints: NS. However,
power during 1-km sprints (undertaken
at [90 % PPO) was significantly
reduced in LCHF-adapt trial
All values are mean ±standard error of the mean
BM body mass, CHO carbohydrate, CI confidence interval, Eenergy, HC high carbohydrate, LCHF low-carbohydrate high-fat diet, Mmale, MCT medium-chain triglyceride, NS not
significantly different, PPO peak power output, TT time trial, VO2max maximal oxygen uptake
High-Fat Diets and Sports Performance S43
123
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carbohydrate diet or 7 days of high-carbohydrate diet before
undertaking a laboratory-based cycling protocol designed to
test some of the features of endurance sporting events.
Specifically, cyclists were required to undertake a series of
sprints throughout the self-paced 100-km trial: 4-km sprints
undertaken at *78–84 % peak power output and 1-km
sprints undertaken at[90 % peak power output (see Fig. 3).
Overall, differences in the performance times for the 100-km
time trial (TT) were not statistically significant, although the
mean performance on the high-carbohydrate trial was 3 min
44 s or *2.5 % faster (153 min, 10 s for high-carbohydrate
trial and 156 min, 53 s for LCHF adapted, p=0.23). While
there was no difference between trials with regard to the
4-km sprint times, performance of the 1-km sprints was
significantly impaired in the LCHF-adapted trial in all sub-
jects, including the three subjects whose overall 100-km TT
performance was faster than in their high-carbohydrate trial.
The authors stated that although adaptation to the LCHF diet
followed by carbohydrate restoration increased fat oxidation
during exercise, ‘‘it reduced high-intensity sprint power
performance, which was associated with increased muscle
recruitment, effort perception and heart rate’’.
Although the mechanisms associated with the compro-
mised performance in this study were unclear, speculations
by the authors included ‘‘increased sympathetic activation,
or altered contractile function and/or the inability to oxi-
dize the available carbohydrate during the high intensity
sprints’’. Indeed, evidence for this latter suggestion was
provided by data from this author’s own laboratory col-
lected contemporaneously. In an investigation of possible
mechanisms to explain the performance outcomes
associated with the LCHF-adaptation and carbohydrate-
restoration model, we examined muscle metabolism at rest,
during sub-maximal exercise, and after an all-out 1-min
sprint following the usual dietary treatment (Fig. 4)[46].
In comparison with the control trial (high-carbohydrate
diet), we found that adaptation to the LCHF diet and
subsequent restoration of muscle glycogen was associated
with a reduction in glycogenolysis during exercise, and a
reduction in the active form of pyruvate dehydrogenase
(PDHa) at rest, during submaximal cycling, and during
sprint cycling. Explanations for the down-regulated activ-
ity of this enzyme complex responsible for linking the
glycolytic pathway with the citric acid cycle included the
observed post-sprint decrease in concentrations of free
adenosine monophosphate (AMP) and adenosine diphos-
phate (ADP) and potentially an up-regulation of PDH
kinase (PDK) activity, which has previously been observed
in association with a high-fat diet [47]. This study provided
evidence of glycogen ‘impairing’ rather than ‘sparing’ in
response to adaptation to an LCHF diet and a robust
explanation for the impairment of key aspects of exercise
performance as a result of this dietary treatment.
3.4 Summary of Learnings from the Literature:
1999–2006
Key interpretations by this author from the literature on
adaptation to an LCHF conducted up until 2006 are sum-
marized below:
Power (W)
500 -
450 -
400 -
350 -
300 -
250 -
200 -
10 20 32 40 52 60 72 80 99 km
*
# #
1 km HCHO
1 km FAT-adapt
4 km HCHO
4 km FAT-adapt
1 km and 4 km sprints at designated distances within 100 km time trial
Fig. 3 Power outputs during 1- and 4-km sprints undertaken within a
100-km self-paced cycling time trial after a 6-day high-carbohydrate
diet and 5 days of a low-carbohydrate high-fat diet followed by 1 day
of a high-carbohydrate diet (fat-adapt) [1]. 100-km total time: 153:10
vs. 156:54 min for carbohydrate vs. FAT-adapt, not significant.
Values are means ±standard deviation for eight well-trained cyclists.
Power outputs decreased over time in both trials with 4-km sprints
(
#
p\0.05), but did not differ between trials. However, with the 1-km
sprints, mean power was significantly lower after the fat-adaptation
treatment (Fat-adapt) compared with the high-carbohydrate diet
(*p\0.05). Reproduced from Havemann et al. [1] with permission.
HCHO high carbohydrate
20 min @ 70% VO2max
4-
3-
2-
1-
1 min @ 150% PPO
0 1 20 min
PDH activity (mmol/kg ww/min)
HCHO
FAT-adapt
*
*
*
*
Fig. 4 Pyruvate dehydrogenase activity in the active form at rest,
during 20 min of cycling at *70 % maximal aerobic capacity
followed by a 1-min sprint at 150 % of peak power output after either
a 5-day adaptation to a low-carbohydrate high-fat diet followed by a
1-day high-carbohydrate diet (FAT-adapt) or 6 days of a high-
carbohydrate diet. Values are means ±standard error of the mean for
seven well-trained cyclists. *Different from 0 min,
à
trial effect:
HCHO trial [FAT-adapt trial;
time point: HCHO trial [FAT-
adapt where significance is set at p\0.05. Reproduced from
Stellingwerff et al. [46] with permission. HCHO high carbohydrate,
PDH pyruvate dehydrogenase, PPO peak power output, VO
2
max
maximal aerobic capacity
S44 L. M. Burke
123
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1. Exposure to an LCHF diet in the absence of ketosis
causes key adaptations in the muscle in as little as
5 days to retool its ability to oxidize fat as an exercise
substrate. Adaptations include, but are not limited to,
an increase in IMTG stores, increased activity of the
hormone-sensitive lipase (HSL) enzyme, which mobi-
lizes triglycerides in muscle and adipose tissue,
increases in key fat-transport proteins such as fatty
acid translocase [FAT-CD36] and carnitine-palmitoyl
transferase (CPT) (for extended review, see Yeo et al.
[29]). Together, these adaptations further increase the
already enhanced capacity of the aerobically trained
muscle to utilize endogenous and exogenous fat stores
to support the fuel cost of exercise of moderate
intensity. Rates of fat oxidation during exercise may be
doubled by fat-adaptation strategies.
2. These muscle-retooling activities stimulated by fat
adaptation are sufficiently robust that they persist in
the face of at least 36 h of aggressive dietary strategies
to increase carbohydrate availability during exercise
(e.g., glycogen supercompensation, pre-exercise car-
bohydrate intake, high rates of carbohydrate intake
during exercise). Although the increased carbohydrate
availability reduces rates of fat oxidation compared
with fat adaptation alone, fat utilization remains
similarly elevated above comparative rates in the
absence of fat adaptation. The time course of the
‘washout’ of retooling is unknown.
3. In addition to up-regulating fat oxidation at rest and
during exercise, exposure to an LCHF diet down-
regulates carbohydrate oxidation during exercise.
Direct [34,42,45] and indirect [45] techniques of
measuring the source of changes in substrate utiliza-
tion show that changes in utilization of muscle
glycogen, rather than blood glucose or exogenous
glucose, account for the change in carbohydrate use.
The reduction in glycogen use persists in the face of
glycogen supercompensation [45] and high-intensity
exercise [46], noting that it is robust and independent
of substrate availability. A down-regulation of PDH
activity explains at least part of the impairment of
glycogen utilization as an exercise fuel [46], repre-
senting a decrease in metabolic flexibility.
4. Despite the enhanced capacity for utilization of a
relatively limitless fuel source as an exercise substrate,
fat-adaptation strategies with or without restoration of
carbohydrate availability do not appear to enhance
exercise capacity or performance per se. Several inter-
related explanations are possible for the failure to
observe benefits:
Type II statistical error: failure to detect small but
important changes in performance due to small
sample sizes [34], individual responses [42,45],
and poor reliability of the performance protocol.
While this explanation often looks attractive [43],
in some cases, further exploration and enhanced
sample size increases confidence in the true
absence of a performance enhancement [43].
Benefits are limited to specific scenarios: charac-
teristics of conditions under which fat-adaptation
strategies appear to be more likely to be beneficial
include protocols of prolonged sub-maximal exer-
cise in which pre-exercise glycogen is depleted
and/or no carbohydrate is consumed during exer-
cise (e.g., low-carbohydrate availability).
Benefits are limited to specific individuals: char-
acteristics of individuals who may respond to fat-
adaptation strategies include carbohydrate-sensi-
tive individuals who are subjected to scenarios in
which carbohydrate cannot be consumed during
exercise.
5. The experience of athletes, at least in the short-term
exposure to LCHF diets, is of a reduction in training
capacity and increase in perceived effort, heart rate,
and other monitoring characteristics, particularly in
relation to high-intensity/quality training, which plays
a core role in a periodized training program [40].
6. Fat-adaptation strategies may actually impair exercise
performance, particularly involving shorter high-inten-
sity events or high-intensity phases during a longer
event, which require power outputs or intensities of
85–90 % maximum level or above. This is likely to be
due to the impairment of the muscle glycogen
utilization needed to support high work rates, even in
scenarios where strategies to achieve high carbohy-
drate availability are employed.
On the basis that conventional competitive sports gen-
erally provide opportunities to achieve adequate carbohy-
drate availability, that fat-adaptation strategies reduce
rather than enhance metabolic flexibility by reducing car-
bohydrate availability and the capacity to use it effectively
as an exercise substrate, and that athletes would be unwise
to sacrifice their ability to undertake high-quality training
or high-intensity efforts during competition that could
determine the outcome of even an ultra-endurance sport,
this author decided to abandon a research and practical
interest in fat-adaptation strategies. A meta-analysis pub-
lished about the same time on the effect of the carbohy-
drate and fat content of athletic diets on endurance
performance [48] summarized that the heterogeneity
around their findings that high-carbohydrate diets (defined
as [50 % of energy from carbohydrate) have a moderate
(effect size 0.6) benefit on exercise capacity compared with
high-fat diets (defined as [30 % of energy from fat)
High-Fat Diets and Sports Performance S45
123
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showed that ‘‘a conclusive endorsement of a high-carbo-
hydrate diet is hard to make’’. However, this heterogeneity
speaks to the limitations of undertaking a meta-analysis
with such a broad and undefined theme as well as the
problem of the ‘black and white’ thinking that is discussed
in the conclusion to this review.
4 Update on Fat Adaptation Literature Since 2006
Given the recent escalation in the promotion of LCHF diets
for sports performance, it could be assumed that the last
decade has seen the publication of a considerable number of
studies with clear evidence of benefits to sports performance
following the implementation of fat-adaptation strategies.
Yet, to the knowledge of this author, only two new investi-
gations of LCHF diets in athletes have appeared in the peer-
reviewed literature since 2006 [49,50]. These studies,
summarized in Table 2, fail to show performance benefits
associated with a ketogenic LCHF diet, although there is
evidence of a small but favorable reduction in body fat levels.
Nevertheless, there are some peculiarities with the design or
methodologies of these studies, including the failure of one
study to achieve the carbohydrate restriction typically
associated with the ketogenic LCHF diet, and they have
failed to become widely cited, even by supporters of the
LCHF movement. Rather, the current interest in chronic
application of LCHF eating by athletes appears to be driven
by enthusiastic discussion in lay and social media by
(mostly) non-elite athletes of sporting success following
experimentation with such diets as well as a range of outputs
from several sports scientists who are researchers and
advocates of this eating style [38]. It is uncertain whether
there is a cause–effect relationship between these sources (or
the direction of any relationship), but the fervor merits
attention. In the absence of compelling new data, the reader
is alerted to several elements in the discussions that are
positive and some that are concerning:
1. Peer-reviewed publications from the key scientific
protagonists of the LCHF movement [3,5,6] generally
show measured and thoughtful insights, based on a re-
examination of previously conducted studies, personal
experiences, anecdotal observations from the sports
world, and the general interest in tackling modern
health problems with the LCHF approach [51,52]. In
these forums, the discussion points include the lack of
evidence and equivocal outcomes of research to
support the performance benefits of LCHF but also
theoretical constructs around potential benefits to
metabolism, muscle, and brain function, inflammatory
and oxidative status, and body composition manage-
ment. Discussion generally targets the potential for
‘some’’ [5] athletes to respond to this different dietary
approach, with this being promoted to ‘‘individuals’’,
‘ultra-endurance athletes’’, and ‘‘athletes involved in
submaximal endurance exercise’’ [6] while being
discouraged for use by athletes involved in ‘‘anaerobic
performance or most conditions of competitive
athletics’’ [6]. While there are some suggestions that a
larger group of athletes might benefit from an LCHF
approach, the general tone is that further investigation
of these theories is required [36].
2. The apparent caution expressed in peer-reviewed publi-
cations is generally not present in other outputs from the
same authors. Laybooks [7], web-based information, and
social media [8,9] enthusiastically promote the LCHF
dietary approach for a larger group of athletes or athletes
in general, with a positive view that this is an evidence-
based strategy: ‘[in regard to endurance events
(60–80 % VO
2
max)]: I don’t think there’s much doubt
that a low-carb high-fat diet is better. That’s because you
have enough fat stores to run for hours and hours and
hours. You don’t have many carbohydrate stores to allow
you to run for very long. Many of the world’s top
endurance athletes have gone low carb, high fat’’ [8]. The
differences between these viewpoints can be confusing,
as is the misrepresentation of the physiological require-
ments of competitive sports (see Sect. 2).
3. The current focus of the LCHF diet movement appears
to lie in ketogenic adaptation, or chronic adaptation to
a carbohydrate-restricted diet (\50 g/day carbohy-
drate) with high fat intakes ([80 % of energy).
Additionally recommended characteristics include
maintenance of moderate protein intake at *15 % of
energy or *1.5 g/kg/day, with the note that intake
should not exceed 25 % of energy intake or ketosis
will be suppressed, and the need to ensure adequate
intake of sodium and potassium at 3–5 and 2–3 g/day,
respectively [6]. Many of the theorized benefits from
the LCHF diet are claimed to come from the adapta-
tion to high circulating levels of ketone bodies, which
provide an additional fuel source for the brain and
muscle as well as achieve other health and functional
benefits [5,6]. The amount of energy that can be
provided by ketones as an exercise substrate has been
neither calculated nor measured, making it impossible
to verify this claim. The time required to achieve
optimal adaptation (and, therefore, the period that
requires investigation in new studies) is claimed to be
at least 2–3 weeks, with at least 1 week required
before the feelings of lethargy and reduced exercise
capacity abate [5,6]. With such chronic keto-adapta-
tion, it is considered unnecessary to consume carbo-
hydrate during exercise, or perhaps to consume it in
small amounts [5,6]. As has been discussed in this
S46 L. M. Burke
123
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
review, the current evidence for these claims is
equivocal and mostly anecdotal. Until or unless further
research is undertaken, we are unlikely to resolve any
of the current questions and claims. The role of non-
ketogenic LCHF diets is not clear.
4. The current literature on LCHF diets is relentless in
promoting misunderstanding or misinformation on the
current guidelines for athletes in relation to carbohy-
drate intake in the training or competition diet. These
guidelines have been provided in Table 1to frame the
current discussions, and contrast strongly with the
information presented by LCHF supporters: ‘‘In stark
contrast to long-standing dogma in sports nutrition
emphasizing the essential need for CHO in all forms of
exercise regardless of duration or intensity ’’ [ 5].
‘Exercise scientists teach that since muscle glycogen
utilization occurs at high rates (during high-intensity
exercise in CHO-adapted athletes), all athletes must be
advised to ingest large amounts of CHO before and
during exercise’’ [3]. As a contributor to the evolution
of the current sports nutrition guidelines, which have
moved away from a universal approach to any aspect
of the athlete’s diet, with particular effort to promote
an individualized and periodized approach to both
carbohydrate intake and carbohydrate availability
during the training phase [53], this author finds such
misrepresentation to be a disappointing thread.
5 Summary and Future Directions
It would benefit sports nutrition for researchers and prac-
titioners to show mutual respect in recognizing the evolu-
tion of new ideas and the replacement of old guidelines
with new recommendations [53]. Indeed, modern sports
nutrition practitioners teach athletes to manipulate their
eating practices to avoid unnecessary and excessive intakes
of carbohydrates per se, to optimize training outcomes via
modification of the timing, amount and type of carbohy-
drate-rich foods and drinks to balance periods of low- and
high-carbohydrate availability and to adopt well-practiced
competition strategies that provide appropriate carbohy-
drate availability according to the needs and opportunities
provided by the event and individual experience [14,54
57]. It is important to consider insights from research and
athlete testimonials to identify different scenarios in which
one approach might offer advantages over another or to
explain divergent outcomes (Table 5), rather than insist on
a single ‘truth’ or solution. Indeed, although there is a
continual cry to rid sports nutrition of ‘dogma’ [4], it would
seem counterproductive if new ideas were as dogmatic as
the old beliefs they seek to replace. This author and others
continue to undertake research to evolve and refine the
understanding of conditions in which low carbohydrate
availability can be tolerated or actually beneficial [58,59].
However, we also recognize that the benefits of carbohy-
drate as a substrate for exercise across the full range of
exercise intensities via separate pathways [16], the better
economy of carbohydrate oxidation versus fat oxidation
(ATP produced per L of oxygen combusted) [60], and the
potential CNS benefits of mouth sensing of carbohydrate
[61] can contribute to optimal sporting performance and
should not be shunned simply because of the lure of the
size of body fat stores. In other words, there should not be a
choice of one fuel source or the other, or ‘black versus
white’, but rather a desire to integrate and individualize the
various dietary factors that can contribute to optimal sports
performance.
Table 5 Scenarios or explanations for testimonials/observations of enhanced performance following change to a low-carbohydrate high-fat diet
Scenarios favoring adaptation to LCHF diet Other explanations for anecdotal reports of performance benefits from
switching to LCHF diet
Individuals or events involving prolonged sub-maximal effort where
there is no benefit or requirement for higher-intensity pieces
Individuals or events in which it is difficult to consume adequate CHO
to meet goals for optimal CHO availability (e.g., gastrointestinal
upsets, logistical difficulties with accessing supplies during the event)
Individuals who are carbohydrate sensitive and likely to be exposed to
low CHO availability
Switch to LCHF has been associated with loss of body fat and increase
in power-to-mass ratio
Previous diet and training were sub-optimal, and switch has been
associated with greater training and diet discipline
Order effect: natural progress in training and maturation in age and
sporting experience
Previous program did not include accurate measurement of
performance: awareness of performance metrics just commenced
Placebo effect/excitement about being part of new idea/culture
Athlete is not actually adhering to LCHF diet, due to misunderstanding
of its true composition or own ‘tweaking’ activities, such that eating
patterns include sufficient CHO around key training sessions and
competition to promote high CHO availability
CHO carbohydrate, LCHF low-carbohydrate high-fat diet
High-Fat Diets and Sports Performance S47
123
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
The science and practice of these strategies is still
evolving, and indeed, a final comment by this author on the
current literature on LCHF diets for sports performance is
that another reason for considering it incomplete is that the
optimal ‘control’ (or additional intervention) diet has not
yet been included in comparisons with fat-adaptation
techniques. Future studies should investigate various
LCHF strategies in comparison with the evolving model of
the ‘carbohydrate-periodized’ training diet, rather than (or
as well as) a diet chronically high in carbohydrate avail-
ability, to determine the best approaches for different
individuals, different goals, and preparation for different
sporting events. Considering that athletes might best ben-
efit from a range of options in the dietary tool box is likely
to be a better model for optimal sports nutrition than
insisting on a single, one-size-fits-all solution.
Acknowledgments This article was published in a supplement
supported by the Gatorade Sports Science Institute (GSSI). The
supplement was guest edited by Lawrence L. Spriet, who attended a
meeting of the GSSI expert panel (XP) in March 2014 and received
honoraria from the GSSI for his participation in the meeting. He
received no honoraria for guest editing the supplement. Dr. Spriet
selected peer reviewers for each paper and managed the process.
Louise Burke attended a meeting of GSSI XP in February 2014, and
her workplace (Australian Institute of Sport) received an honorarium
from the GSSI, a division of PepsiCo, Inc., for her meeting partici-
pation and the writing of this manuscript. The views expressed in this
manuscript are those of the author and do not necessarily reflect the
position or policy of PepsiCo, Inc. Research undertaken by this author
in relation to fat-adaptation strategies was funded by grants from the
Australian Institute of Sport, Kellogg’s Australia, and Nestle
Australia.
Open Access This article is distributed under the terms of the Crea-
tive Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a link
to the Creative Commons license, and indicate if changes were made.
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... Within the last three decades, several studies have indicated an improved fat metabolism under resting and submaximal exercise conditions following longterm (! 2 weeks) high fat diets (Phinney et al. 1983;Lambert et al. 1994;Rowlands and Hopkins 2002;Zajac et al. 2014;Volek et al. 2016;Burke et al. 2017). However, in most studies with prolonged high fat diets, there was only a small positive (or even negative) effect on performance during competitioneven with a prior carbohydrate restoration phase to prevent low pre-competition glycogen storages (Burke 2015). ...
... Hence, performance at a higher intensity level is impaired to the reduced ability to metabolise carbohydrates. Furthermore, high fat diets are accompanied by side effects since fatigue or poor concentration due to an insufficient provision of micronutrients and glycogen during training sessions play a crucial role in the preparation of competition (Burke 2015;Tiller et al. 2019). ...
... Some studies confirmed, that a high fat diet has a positive impact on performance at submaximal intensities (Phinney et al. 1983;Lambert et al. 1994;Rowlands and Hopkins 2002). Despite an improved fat metabolism under resting conditions and during submaximal exercise, there is a growing body of evidence that these metabolic changes induced by ketogenic or nonketogenic high fat diets are not associated with an improved endurance performance e.g. during competition (Burke 2015;Burke et al. 2017;Zinn et al. 2017;Durkalec-Michalski et al. 2021). Although endurance competitions are predominantly characterised by submaximal intensities, high intensities (e.g. ...
Article
Full-text available
The present study investigated the effect of a 4-week high fat low carbohydrate (HFLC-G) versus high carbohydrate low glycaemic (LGI-G) or high glycaemic (HGI-G) diet on power output at lactate thresholds, peak oxygen uptake and peak performance during an incremental cycle test in 28 male endurance athletes. All participants showed improved levels of power output at the lactate thresholds with a more pronounced effect in the HFLC-G and LGI-G. In the HFLC-G peak performance (-11.6 ± 16.3 W) decreased, while in the LGI-G (9.20 ± 13.8 W) and HGI-G (9.89 ± 12.8 W) peak performance increased (p = 0.009). In summary, the LGI-G showed comparable training adaptations as the HFLC-G at submaximal intensities without limiting the ability to perform at high intensities. Compared to a HFLC and HGI diet, the LGI diet in this study seemed to be advantageous during submaximal and high intensities resulting from an improved metabolic flexibility.
... The concept of a high-fat (>60% of daily energy intake) and low-carbohydrate (<25% of daily energy intake) diet has been discussed since 1985. The current state of evidence suggests a diet with less than 50 g of carbohydrates per day (9). A metabolic adaptation toward increased fat oxidation is usually achieved following a 2-to 4-week dietary intervention (9,10). ...
... The current state of evidence suggests a diet with less than 50 g of carbohydrates per day (9). A metabolic adaptation toward increased fat oxidation is usually achieved following a 2-to 4-week dietary intervention (9,10). However, high fat diets are associated with an impaired carbohydrate utilization during higher intensities (11)(12)(13)(14) and, consequently, with small positive effects on endurance performance even with a carbohydrate restoration phase prior to competitions (9). ...
... A metabolic adaptation toward increased fat oxidation is usually achieved following a 2-to 4-week dietary intervention (9,10). However, high fat diets are associated with an impaired carbohydrate utilization during higher intensities (11)(12)(13)(14) and, consequently, with small positive effects on endurance performance even with a carbohydrate restoration phase prior to competitions (9). This altered metabolic flexibility can be explained by a reduced enzyme activity in the carbohydrate metabolism due to a reduced training effect within the carbohydrate metabolism following reduced carbohydrate availability or reduced signaling at low glycogen concentrations (2,3). ...
Article
Full-text available
Consuming low glycemic carbohydrates leads to an increased muscle fat utilization and preservation of intramuscular glycogen, which is associated with improved flexibility to metabolize either carbohydrates or fats during endurance exercise. The purpose of this trial was to investigate the effect of a 4-week high fat low carbohydrate (HFLC-G: ≥65% high glycemic carbohydrates per day; n = 9) vs. high carbohydrate low glycemic (LGI-G: ≥65% low glycemic carbohydrates daily; n = 10) or high glycemic (HGI-G: ≥65% fat, ≤ 50 g carbohydrates daily; n = 9) diet on fat and carbohydrate metabolism at rest and during exercise in 28 male athletes. Changes in metabolic parameters under resting conditions and during cycle ergometry (submaximal and with incremental workload) from pre- to post-intervention were determined by lactate diagnostics and measurements of the respiratory exchange ratio (RER). Additionally, body composition and perceptual responses to the diets [visual analog scale (VAS)] were measured. A significance level of α = 0.05 was considered. HFLC-G was associated with markedly decreased lactate concentrations during the submaximal (−0.553 ± 0.783 mmol/l, p = 0.067) and incremental cycle test [−5.00 ± 5.71 (mmol/l) × min; p = 0.030] and reduced RER values at rest (−0.058 ± 0.108; p = 0.146) during the submaximal (−0.078 ± 0.046; p = 0.001) and incremental cycle test (−1.64 ± 0.700 RER × minutes; p < 0.001). In the HFLC-G, fat mass (p < 0.001) decreased. In LGI-G lactate, concentrations decreased in the incremental cycle test [−6.56 ± 6.65 (mmol/l) × min; p = 0.012]. In the LGI-G, fat mass (p < 0.01) and VAS values decreased, indicating improved levels of gastrointestinal conditions and perception of effort during training. The main findings in the HGI-G were increased RER (0.047 ± 0.076; p = 0.117) and lactate concentrations (0.170 ± 0.206 mmol/l, p = 0.038) at rest. Although the impact on fat oxidation in the LGI-G was not as pronounced as following the HFLC diet, the adaptations in the LGI-G were consistent with an improved metabolic flexibility and additional benefits regarding exercise performance in male athletes.
... Even so, the evidence base for this dietary intervention and its potential effects is still unclear and conflicting. Additionally, the evidence against or in favor of KD on physical performance and body composition has been reported mainly by narrative (Noakes, Volek, and Phinney 2014;Burke 2015Burke , 2021Paoli, Bianco, andGrimaldi 2015, Paoli et al. 2019;Volek, Noakes, and Phinney 2015;Tinsley and Willoughby 2016;Chang, Borer, and Lin 2017;Ashtary-Larky, Bagheri, Bavi, et al. 2021;Valenzuela et al. 2021) or systematized reviews Coleman, Carrigan, and Margolis 2021;Murphy, Carrigan, and Margolis 2021). Given this lack of robust knowledge, this review aimed to assess the studies published via a systematic review and perform a meta-analysis and, when appropriate, a meta-regression under the Bayesian framework about the effects of KD compared to rich CHO diets on physical performance and body composition on adult athletes and trained individuals. ...
... This review is no longer lasting word on KD against CHO-rich diets. However, the results are an additional hammer in the coffin nail (c.f., (Burke and Kiens 2006;Burke 2015)) for KD interventions for up to 12 weeks in well-trained athletes of moderate-to high-intensity endurance events performance. Additionally, KD effects differed depending on the motor pattern of exercise and subjects' sex, being more impaired in relation to CHO-rich diets during running than cycling and in women than men. ...
Article
This systematic review with meta-analysis aimed to determine the effects of the ketogenic diet (KD) against carbohydrate (CHO)-rich diets on physical performance and body composition in trained individuals. The MEDLINE, EMBASE, CINAHL, SPORTDiscus, and The Cochrane Library were searched. Randomized and non-randomized controlled trials in athletes/trained adults were included. Meta-analytic models were carried out using Bayesian multilevel models. Eighteen studies were included providing estimates on cyclic exercise modes and strength one-maximum repetition (1-RM) performances and for total, fat, and free-fat masses. There were more favorable effects for CHO-rich than KD on time-trial performance (mode [95% credible interval]; −3.3% [−8.5%, 1.7%]), 1-RM (−5.7% [−14.9%, 2.6%]), and free-fat mass (−0.8 [−3.4, 1.9] kg); effects were more favorable to KD on total (−2.4 [−6.2, 1.8] kg) and fat mass losses (−2.4 [−5.4, 0.2] kg). Likely modifying effects on cyclic performance were the subject’s sex and VO2max, intervention and performance durations, and mode of exercise. The intervention duration and subjects’ sex were likely to modify effects on total body mass. KD can be a useful strategy for total and fat body losses, but a small negative effect on free-fat mass was observed. KD was not suitable for enhancing strength 1-RM or high-intensity cyclic performances.
... Ancak, dayanıklılık/ultra-dayanıklılık sporlarında performansa net faydalarının tespit edilememesi, karbonhidrat metabolizmasının bozulması yoluyla yüksek yoğunluklu egzersiz performansında düşüş riskinin görülebilmesi sonucu, sporcular tarafından uygulanmaması gerektiği belirtilmektedir. 10 Substratın diyetteki dağılımı ayrıca egzersiz süresi boyunca hangi substratın kullanılacağını belirlemektedir. Bir sporcu yüksek karbonhidratlı bir diyet tüketiyorsa, egzersiz için yakıt olarak daha fazla glikojen kullanacaktır. ...
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ÖZET Hayvansal ve bitkisel kaynaklı olan yağlar, insan vücuduna alınarak metabolik faaliyetlerin gerçekleştirilmesinde kullanılmaktadır. Uluslararası Spor Beslenmesi Birliği'ne (ISSN) göre; sporcular için diyet yağı alımı, sporcu olmayan bireylere yapılan önerilere benzerdir ve günlük enerji alımlarının yaklaşık %30'u kadar yağ tüketmeleri önerilmektedir. Amerikan Spor Hekimliği Koleji (ACSM), yağ tüketiminin alınan enerjinin %20'sinden az olması durumunda, spor performansını olumsuz etkilediğini belirtmektedir. Ayrıca, yorgunluğun ve yaralanma riskinin artması söz konusudur. Vücut yağ yüzdesi, sporcunun cinsiyetine ve spor dalına bağlı olarak değişmektedir ancak spor dalına göre hangi yağ yüzdesinin uygun olduğu konusunda görüş birliğine varılamamıştır. Diyetleri omega-3 yağ asidinden zengin olan sporcularda, egzersiz sonrası kas ağrısı ve inflamasyonun azaldığı ve toparlanmanın daha hızlı olduğu gösterilmiştir. Yüksek yağlı, düşük karbonhidratlı diyetler, yağ oksidasyonunu artırmakta ancak performans üzerindeki etkilerinin belirlenebilmesi için daha fazla araştırmaya ihtiyaç bulunmaktadır. Anahtar Kelimeler: Diyet yağı; spor performansı; yüksek yağlı diyet ABSTRACT Fats of animal and vegetable origin are taken into the human body and used for the realization of metabolic activities. According to the International Society of Sports Nutrition (ISSN); dietary fat intake for athletes is similar to recommendations for non-athletes and is recommended to consume about 30% of their daily energy intake. The American College of Sports Medicine (ACSM) states that if fat consumption is less than 20% of the energy intake, it affects sports performance negatively. There is also an increased risk of fatigue and injury. The percentage of body fat varies depending on the athlete's sex and sport, but there is no consensus as to which fat percentage is appropriate for the sport. In athletes whose diet is rich in omega-3 fatty acid, muscle pain and inflammation have been shown to decrease after exercise and recovery is faster. High-fat, low-carb diets increase fat oxidation, but further research is needed to determine their impact on performance. Keywords: Dietary fat; sports performance; high fat diet
... Due to limited endogenous carbohydrate availability [20,21] in endurance sports such as road cycling and cross-country skiing, energy requirements for races can exceed the capacity to store carbohydrates by more than 100% [22,23]. Thus, strategies have been proposed to circumvent this issue, such as increasing carbohydrate storage before the start of competition [24]-also known as carbohydrate or glycogen loading, increasing exogenous carbohydrate availability by carbohydrate feeding during exercise [25] and/ or reducing reliance on endogenously stored carbohydrates while increasing the utilization of fatty acids [26]. ...
Article
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The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.
... Conversely, low carbohydrate intakes may lead to glycogen depletion, fatigue, and inadequate recovery between training sessions (6). In fact, low carbohydrate intakes have been identified as a characteristic of people with an increased risk of LEA (22). ...
Article
Monedero, J, Duff, C, and Egan, B. Dietary intakes and the risk of low energy availability in male and female advanced and elite rock climbers. J Strength Cond Res XX(X): 000–000, 2022—There is a culture among rock climbers of striving to maintain low body mass and percentage body fat to enhance performance. Diet practices based on this belief might lead to increased risk of low energy availability (LEA) or eating disorders (EDs). Twenty-five advanced or elite rock climbers (male, n = 14; female, n = 11) had body composition measured, completed 4-day food intake and physical activity diaries while wearing an accelerometer and heart rate monitor, and completed the Eating Attitudes Test (EAT)-26 and the Low Energy Availability in Females Questionnaire (LEAF-Q; n = 11 female subjects only). EAT-26 scores of 3.5 (1.8, 7.0) [median (IQR)] and 9.3 ± 6.4 (mean ± SD) for male and female subjects, respectively, indicated low risk of ED in this cohort, but 4 female subjects were at high risk of LEA according to LEAF-Q scores. Suboptimal (<45 kcal·kg·FFM−1·d−1) and LEA (<30 kcal·kg·FFM−1·d−1) were evident in 88 and 28%, respectively, of climbers. However, only the female climbers had energy intakes (1775 ± 351 kcal·d−1) significantly lower than their calculated energy requirements (2056 ± 254 kcal·d−1; p = 0.006). In all subjects, carbohydrate intakes were lower (male subjects: 3.8 ± 1.2 g·kg−1·d−1, p = 0.002; female subjects: 3.4 ± 0.7 g·kg−1·d−1, p < 0.001), and fat intakes were higher (male subjects: 1.6 ± 0.5 g·kg−1·d−1, p < 0.001; female subjects: 1.4 ± 0.4 g·kg−1·day−1, p < 0.001) than current sports nutrition recommendations, and inadequate intakes of calcium, magnesium, and vitamin D were observed. Female subjects specifically had lower than recommended intakes of protein and iron. These results show that advanced and elite rock climbers have a high prevalence of LEA and have a risk of having nutritional deficiencies as result of their diet.
... Whether a high-fat diet could be a strategy for improving endurance in athletes, via this effect on lipid oxidation, has been largely investigated over the two last decades [185]. In fact, this fat-diet-induced shift in substrate oxidation has been shown to impair endurance exercise metabolism and performance despite enhanced glycogen availability, and thus has little effect on athletes [186]. Furthermore, this aspect has been mostly investigated in athletes, whose metabolism involves important rates of lipid oxidation, and it is clear, on the other hand, that a high-fat diet induces insulin resistance and thus impairs carbohydrate metabolism [187][188][189], whether this fat is saturated or unsaturated [190]. ...
Article
Recent literature shows that exercise is not simply a way to generate a calorie deficit as an add-on to restrictive diets but exerts powerful additional biological effects via its impact on mitochondrial function, the release of chemical messengers induced by muscular activity, and its ability to reverse epigenetic alterations. This review aims to summarize the current literature dealing with the hypothesis that some of these effects of exercise unexplained by an energy deficit are related to the balance of substrates used as fuel by the exercising muscle. This balance of substrates can be measured with reliable techniques, which provide information about metabolic disturbances associated with sedentarity and obesity, as well as adaptations of fuel metabolism in trained individuals. The exercise intensity that elicits maximal oxidation of lipids, termed LIPOXmax, FATOXmax, or FATmax, provides a marker of the mitochondrial ability to oxidize fatty acids and predicts how much fat will be oxidized over 45–60 min of low- to moderate-intensity training performed at the corresponding intensity. LIPOXmax is a reproducible parameter that can be modified by many physiological and lifestyle influences (exercise, diet, gender, age, hormones such as catecholamines, and the growth hormone-Insulin-like growth factor I axis). Individuals told to select an exercise intensity to maintain for 45 min or more spontaneously select a level close to this intensity. There is increasing evidence that training targeted at this level is efficient for reducing fat mass, sparing muscle mass, increasing the ability to oxidize lipids during exercise, lowering blood pressure and low-grade inflammation, improving insulin secretion and insulin sensitivity, reducing blood glucose and HbA1c in type 2 diabetes, and decreasing the circulating cholesterol level. Training protocols based on this concept are easy to implement and accept in very sedentary patients and have shown an unexpected efficacy over the long term. They also represent a useful add-on to bariatric surgery in order to maintain and improve its weight-lowering effect. Additional studies are required to confirm and more precisely analyze the determinants of LIPOXmax and the long-term effects of training at this level on body composition, metabolism, and health.
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Ketogenic diets and orally administered exogenous ketone supplements are strategies to increase serum ketone bodies serving as an alternative energy fuel for high energy demanding tissues, such as the brain, muscles, and the heart. The ketogenic diet is a low-carbohydrate and fat-rich diet, whereas ketone supplements are usually supplied as esters or salts. Nutritional ketosis, defined as serum ketone concentrations of ≥ 0.5 mmol/L, has a fasting-like effect and results in all sorts of metabolic shifts and thereby enhancing the health status. In this review, we thus discuss the different interventions to reach nutritional ketosis, and summarize the effects on heart diseases, epilepsy, mitochondrial diseases, and neurodegenerative disorders. Interest in the proposed therapeutic benefits of nutritional ketosis has been growing the past recent years. The implication of this nutritional intervention is becoming more evident and has shown interesting potential. Mechanistic insights explaining the overall health effects of the ketogenic state, will lead to precision nutrition for the latter diseases.
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Iwayama, K, Tanabe, Y, Yajima, K, Tanji, F, Onishi, T, and Takahashi, H. Preexercise high-fat meal following carbohydrate loading attenuates glycogen utilization during endurance exercise in male recreational runners. J Strength Cond Res XX(X): 000-000, 2022-This study aimed to investigate whether one preexercise high-fat meal can increase glycogen conservation during endurance exercise, as compared with one preexercise high-carbohydrate meal. Ten young male recreational runners (22.0 ± 0.6 years; 171.3 ± 0.9 cm; 58.3 ± 1.9 kg; maximal oxygen uptake [V̇o2max], 62.0 ± 1.6 ml·kg-1·min-1) completed 2 exercise trials after high-carbohydrate loading: eating a high-carbohydrate (CHO; 7% protein, 13% fat, 80% carbohydrate) meal or eating a high-fat (FAT; 7% protein, 42% fat, 52% carbohydrate) meal 3.5 hours before exercise. The order of the 2 trials was randomized, and the interval between trials was at least 1 week. The experimental exercise consisted of running on a treadmill for 60 minutes at 95% of each subject's lactate threshold. Muscle and liver glycogen content were assessed using noninvasive carbon magnetic resonance spectroscopy before the experimental meal as well as before and after exercise; respiratory gases were measured continuously during exercise. The respiratory exchange ratio during exercise was statistically lower in the FAT trial than in the CHO trial (p < 0.01). In addition, muscle (p < 0.05) and liver (p < 0.05) glycogen utilization during exercise was less in the FAT trial than in the CHO trial. Therefore, one high-fat meal following carbohydrate loading reduced muscle and liver glycogen use during the 60-minute exercise. These results suggest that this dietary approach may be applied as a strategy to optimize energy utilization during endurance exercise.
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Introduction: Obesity effects on kidney function. Urinary disorders after exercise are also common, and probably due to transient hemodynamic problems in the glomerular and tubular renal function. The purpose of this research is to investigate the relationship of BMI with proteinuria and hematuria after one session of intense continuous and interval exercise in girls. Methods: In this quasi-experimental research, 45 hostelry high school girl students with a mean age of 15.18 ± 0.39 years were randomly selected and in three groups of 15, they ran 1600 meters in a continuous and interval manner. Urine test collected before, one and 24 hours after activity. The results were analyzed by SPSS version 16 software and one way ANOVA and Pearson correlation coefficient. Results: Increased proteinuria was significant one hour (P = 0.002) and 24 hours after activity (P = 0.001) in the continuous group. In the continuous group, the relationship between fat percentage (P=0.017) and body mass index (P=0.001) with protein excretion 24 hours after activity was positive and significant. One hour after activity, protein excretion with fat percentage and Body mass index (BMI) had no significant relationship. Hematuria was also not significant after activity. Conclusion: Body mass index (BMI) and fat percentage were effective on protein excretion after one session of intense physical activity and had no significant effect on hematuria. Therefore, overweight people were advised to participate in interval exercise to lose weight.
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Triathlon competitions are performed over markedly different distances and under a variety of technical constraints. In ’standard-distance’ triathlons involving 1.5km swim, 40km cycling and 10km running, a World Cup series as well as a World Championship race is available for ’elite’ competitors. In contrast, ’age-group’ triathletes may compete in 5-year age categories at a World Championship level, but not against the elite competitors. The difference between elite and age-group races is that during the cycle stage elite competitors may ’draft’ or cycle in a sheltered position; age-group athletes complete the cycle stage as an individual time trial. Within triathlons there are a number of specific aspects that make the physiological demands different from the individual sports of swimming, cycling and running. The physiological demands of the cycle stage in elite races may also differ compared with the age-group format. This in turn may influence performance during the cycle leg and subsequent running stage. Wetsuit use and drafting during swimming (in both elite and age-group races) result in improved buoyancy and a reduction in frontal resistance, respectively. Both of these factors will result in improved performance and efficiency relative to normal pool-based swimming efforts. Overall cycling performance after swimming in a triathlon is not typically affected. However, it is possible that during the initial stages of the cycle leg the ability of an athlete to generate the high power outputs necessary for tactical position changes may be impeded. Drafting during cycling results in a reduction in frontal resistance and reduced energy cost at a given submaximal intensity. The reduced energy expenditure during the cycle stage results in an improvement in running, so an athlete may exercise at a higher percentage of maximal oxygen uptake. In elite triathlon races, the cycle courses offer specific physiological demands that may result in different fatigue responses when compared with standard time-trial courses. Furthermore, it is possible that different physical and physiological characteristics may make some athletes more suited to races where the cycle course is either flat or has undulating sections. An athlete’s ability to perform running activity after cycling, during a triathlon, may be influenced by the pedalling frequency and also the physiological demands of the cycle stage. The technical features of elite and age-group triathlons together with the physiological demands of longer distance events should be considered in experimental design, training practice and also performance diagnosis of triathletes.
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In the era of social media there are now many different ways that a scientist can build their public profile; the publication of high-quality scientific papers being just one. While social media is a valuable tool for outreach and the sharing of ideas, there is a danger that this form of communication is gaining too high a value and that we are losing sight of key metrics of scientific value, such as citation indices. To help quantify this, I propose the 'Kardashian Index', a measure of discrepancy between a scientist's social media profile and publication record based on the direct comparison of numbers of citations and Twitter followers.
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Abstract A key element contributing to deteriorating exercise capacity during physically demanding sport appears to be reduced carbohydrate availability coupled with an inability to effectively utilize alternative lipid fuel sources. Paradoxically, cognitive and physical decline associated with glycogen depletion occurs in the presence of an over-abundance of fuel stored as body fat that the athlete is apparently unable to access effectively. Current fuelling tactics that emphasize high-carbohydrate intakes before and during exercise inhibit fat utilization. The most efficient approach to accelerate the body's ability to oxidize fat is to lower dietary carbohydrate intake to a level that results in nutritional ketosis (i.e., circulating ketone levels >0.5 mmol/L) while increasing fat intake for a period of several weeks. The coordinated set of metabolic adaptations that ensures proper interorgan fuel supply in the face of low-carbohydrate availability is referred to as keto-adaptation. Beyond simply providing a stable source of fuel for the brain, the major circulating ketone body, beta-hydroxybutyrate, has recently been shown to act as a signalling molecule capable of altering gene expression, eliciting complementary effects of keto-adaptation that could extend human physical and mental performance beyond current expectation. In this paper, we review these new findings and propose that the shift to fatty acids and ketones as primary fuels when dietary carbohydrate is restricted could be of benefit for some athletes.
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The inability of current recommendations to control the epidemic of diabetes, the specific failure of the prevailing low-fat diets to improve obesity, cardiovascular risk, or general health and the persistent reports of some serious side effects of commonly prescribed diabetic medications, in combination with the continued success of low-carbohydrate diets in the treatment of diabetes and metabolic syndrome without significant side effects, point to the need for a reappraisal of dietary guidelines. The benefits of carbohydrate restriction in diabetes are immediate and well documented. Concerns about the efficacy and safety are long term and conjectural rather than data driven. Dietary carbohydrate restriction reliably reduces high blood glucose, does not require weight loss (although is still best for weight loss), and leads to the reduction or elimination of medication. It has never shown side effects comparable with those seen in many drugs. Here we present 12 points of evidence supporting the use of low-carbohydrate diets as the first approach to treating type 2 diabetes and as the most effective adjunct to pharmacology in type 1. They represent the best-documented, least controversial results. The insistence on long-term randomized controlled trials as the only kind of data that will be accepted is without precedent in science. The seriousness of diabetes requires that we evaluate all of the evidence that is available. The 12 points are sufficiently compelling that we feel that the burden of proof rests with those who are opposed. (C) 2015 The Authors. Published by Elsevier Inc.
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The main objective of this research was to determine the effects of a long-term ketogenic diet, rich in polyunsaturated fatty acids, on aerobic performance and exercise metabolism in off-road cyclists. Additionally, the effects of this diet on body mass and body composition were evaluated, as well as those that occurred in the lipid and lipoprotein profiles due to the dietary intervention. The research material included eight male subjects, aged 28.3 ± 3.9 years, with at least five years of training experience that competed in off-road cycling. Each cyclist performed a continuous exercise protocol on a cycloergometer with varied intensity, after a mixed and ketogenic diet in a crossover design. The ketogenic diet stimulated favorable changes in body mass and body composition, as well as in the lipid and lipoprotein profiles. Important findings of the present study include a significant increase in the relative values of maximal oxygen uptake (VO2max) and oxygen uptake at lactate threshold (VO2 LT) after the ketogenic diet, which can be explained by reductions in body mass and fat mass and/or the greater oxygen uptake necessary to obtain the same energy yield as on a mixed diet, due to increased fat oxidation or by enhanced sympathetic activation. The max work load and the work load at lactate threshold were significantly higher after the mixed diet. The values of the respiratory exchange ratio (RER) were significantly lower at rest and during particular stages of the exercise protocol following the ketogenic diet. The heart rate (HR) and oxygen uptake were significantly higher at rest and during the first three stages of exercise after the ketogenic diet, while the reverse was true during the last stage of the exercise protocol conducted with maximal intensity. Creatine kinase (CK) and lactate dehydrogenase (LDH) activity were significantly lower at rest and during particular stages of the 105-min exercise protocol following the low carbohydrate ketogenic diet. The alterations in insulin and cortisol concentrations due to the dietary intervention confirm the concept that the glucostatic mechanism controls the hormonal and metabolic responses to exercise.
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Abstract Traditional nutritional approaches to endurance training have typically promoted high carbohydrate (CHO) availability before, during and after training sessions to ensure adequate muscle substrate to meet the demands of high daily training intensities and volumes. However, during the past decade, data from our laboratories and others have demonstrated that deliberately training in conditions of reduced CHO availability can promote training-induced adaptations of human skeletal muscle (i.e. increased maximal mitochondrial enzyme activities and/or mitochondrial content, increased rates of lipid oxidation and, in some instances, improved exercise capacity). Such data have led to the concept of 'training low, but competing high' whereby selected training sessions are completed in conditions of reduced CHO availability (so as to promote training adaptation), but CHO reserves are restored immediately prior to an important competition. The augmented training response observed with training-low strategies is likely regulated by enhanced activation of key cell signalling kinases (e.g. AMPK, p38MAPK), transcription factors (e.g. p53, PPARδ) and transcriptional co-activators (e.g. PGC-1α), such that a co-ordinated up-regulation of both the nuclear and mitochondrial genomes occurs. Although the optimal practical strategies to train low are not currently known, consuming additional caffeine, protein, and practising CHO mouth-rinsing before and/or during training may help to rescue the reduced training intensities that typically occur when 'training low', in addition to preventing protein breakdown and maintaining optimal immune function. Finally, athletes should practise 'train-low' workouts in conjunction with sessions undertaken with normal or high CHO availability so that their capacity to oxidise CHO is not blunted on race day.
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Purpose: The purpose of this study was to assess research aimed at measuring performance enhancements that affect success of individual elite athletes in competitive events. Analysis: Simulations show that the smallest worthwhile enhancement of performance for an athlete in an international event is 0.7-0.4 of the typical within-athlete random variation in performance between events. Using change in performance in events as the outcome measure in a crossover study, researchers could delimit such enhancements with a sample of 16-65 athletes, or with 65-260 in a fully controlled study. Sample size for a study using a valid laboratory or field test is proportional to the square of the within-athlete variation in performance in the test relative to the event; estimates of these variations are therefore crucial and should be determined by repeated-measures analysis of data from reliability studies for the test and event. Enhancements in test and event may differ when factors that affect performance differ between test and event; overall effects of these factors can be determined with a validity study that combines reliability data for test and event. A test should be used only if it is valid, more reliable than the event, allows estimation of performance enhancement in the event, and if the subjects replicate their usual training and dietary practices for the study; otherwise the event itself provides the only dependable estimate of performance enhancement. Publication of enhancement as a percent change with confidence limits along with an analysis for individual differences will make the study more applicable to athletes. Outcomes can be generalized only to athletes with abilities and practices represented in the study. Conclusion: estimates of enhancement of performance in laboratory or field tests in most previous studies may not apply to elite athletes in competitive events.
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Laboratory-based studies demonstrate that fueling (carbohydrate; CHO) and fluid strategies can enhance training adaptations and race-day performance in endurance athletes. Thus, the aim of this case study was to characterize several periodized training and nutrition approaches leading to individualized race-day fluid and fueling plans for 3 elite male marathoners. The athletes kept detailed training logs on training volume, pace, and subjective ratings of perceived exertion (RPE) for each training session over 16 wk before race day. Training impulse/load calculations (TRIMP; min x RPE = load [arbitrary units; AU]) and 2 central nutritional techniques were implemented: periodic low-CHO-availability training and individualized CHO- and fluid-intake assessments. Athletes averaged ∼13 training sessions per week for a total average training volume of 182 km/wk and peak volume of 231 km/wk. Weekly TRIMP peaked at 4,437 AU (Wk 9), with a low of 1,887 AU (Wk 16) and an average of 3,082 ± 646 AU. Of the 606 total training sessions, ∼74%, 11%, and 15% were completed at an intensity in Zone 1 (very easy to somewhat hard), Zone 2 (at lactate threshold) and Zone 3 (very hard to maximal), respectively. There were 2.5 ± 2.3 low-CHO-availability training bouts per week. On race day athletes consumed 61 ± 15 g CHO in 604 ± 156 ml/hr (10.1% ± 0.3% CHO solution) in the following format: ∼15 g CHO in ∼150 ml every ∼15 min of racing. Their resultant marathon times were 2:11:23, 2:12:39 (both personal bests), and 2:16:17 (a marathon debut). Taken together, these periodized training and nutrition approaches were successfully applied to elite marathoners in training and competition.
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Abstract The oral-pharyngeal cavity and the gastrointestinal tract are richly endowed with receptors that respond to taste, temperature and to a wide range of specific nutrient and non-nutritive food components. Ingestion of carbohydrate-containing drinks has been shown to enhance endurance exercise performance, and these responses have been attributed to post-absorptive effects. It is increasingly recognised, though, that the response to ingested carbohydrate begins in the mouth via specific carbohydrate receptors and continues in the gut via the release of a range of hormones that influence substrate metabolism. Cold drinks can also enhance performance, especially in conditions of thermal stress, and part of the mechanism underlying this effect may be the response to cold fluids in the mouth. There is also some, albeit not entirely consistent, evidence for effects of caffeine, quinine, menthol and acetic acid on performance or other relevant effects. This review summarises current knowledge of responses to mouth sensing of temperature, carbohydrate and other food components, with the goal of assisting athletes to implement practical strategies that make best use of its effects. It also examines the evidence that oral intake of other nutrients or characteristics associated with food/fluid intake during exercise can enhance performance via communication between the mouth/gut and the brain.