International Journal of Sport Nutrition and Exercise Metabolism, 2019, 29, 141-151
https://doi.org/10.1123/ijsnem.2018-0305© 2019 Human Kinetics, Inc.

SCHOLARLY REVIEWA Framework for Periodized Nutrition for Athletics
Trent Stellingwerff
Canadian Sport Institute Paciﬁc, Athletics Canada, and University of Victoria British Columbia

James P. Morton
Liverpool John Moores University

Louise M. Burke
Australian Institute of Sport and Australian Catholic University
Over the last decade, in support of training periodization, there has been an emergence around the concept of nutritional
periodization. Within athletics (track and ﬁeld), the science and art of periodization is a cornerstone concept with recent
commentaries emphasizing the underappreciated complexity associated with predictable performance on demand. Nevertheless,with varying levels of evidence, sport and event speciﬁc sequencing of various training units and sessions (long [macrocycle;
months], medium [mesocycle; weeks], and short [microcycle; days and within-day duration]) is a routine approach to training
periodization. Indeed, implementation of strategic temporal nutrition interventions (macro, meso, and micro) can support andenhance training prescription and adaptation, as well as acute event speciﬁc performance. However, a general framework on
how, why, and when nutritional periodization could be implemented has not yet been established. It is beyond the scope of thisreview to highlight every potential nutritional periodization application. Instead, this review will focus on a generalized
framework, with speciﬁc examples of macro-, meso-, and microperiodization for the macronutrients of carbohydrates, and, byextension, fat. More speciﬁcally, the authors establish the evidence and rationale for situations of acute high carbohydrate
availability, as well as the evidence for more chronic manipulation of carbohydrates coupled with training. The topic ofperiodized nutrition has made considerable gains over the last decade but is ripe for further scientiﬁc progress and ﬁeld
application.
Keywords: performance, track and ﬁeld, nutrient timing, macro, meso, micro
The concept and underpinnings of periodization are deeply
rooted in the history of athletics (track and ﬁeld). Indeed, the seminal
scientists and coaches who developed the principles of periodization
include Dr. Hans Selye with his General Adaptation Syndromemodel (Selye, 1950), followed by Matveyev, Bonderchuck, andBompa (contributions reviewed by Issurin, 2010). Numerous approaches to periodization have emerged from this work, includingclassical, block, polarized, and complex models (Issurin, 2010;
Kiely, 2012). Within this diversity is a central theme: the purposeful
sequencing of different training units (long [macrocycle; months],
medium [mesocycle; weeks], and short [microcycle; days andwithin-day duration]) so that athletes can attain the desired readinessto perform optimally for targeted events on demand (Stone et al.,1981). However, it is now appreciated that the chaos and complexities of the individual, exposed to various stimuli (physical,
emotional, and genetic), are probably much more complicatedthan most periodization purists would want to admit (Kiely,
Stellingwerff is with Canadian Sport Institute Paciﬁc, Victoria, British Columbia,
Canada; Athletics Canada, Ottawa, Ontario, Canada; and the Dept. of Exercise
Science, Physical & Health Education, University of Victoria, Victoria, British
Columbia, Canada. Morton is with the Research Institute for Sport and Exercise
Sciences, Liverpool John Moores University, Liverpool, United Kingdom. Burke iswith the Australian Institute of Sport, Belconnen, Australia; and the Mary MacKillop
Institute for Health Research, Australian Catholic University, Melbourne, Australia.
Stellingwerff (tstellingwerff@csipaciﬁc.ca) is corresponding author.

2018). Furthermore, the impact of nutrition on training adaptationand performance needs to be recognized.
The 2007 International Association of Athletics Federations
Nutrition Consensus presented the ﬁrst formal opportunity toprovide theoretical guidelines for nutrition periodization, withsuggestions of the approximate energetic and macronutrient demands of different training phases within a yearly periodized
training plan (Stellingwerff et al., 2007). Recently, periodized
nutrition has been deﬁned as “the planned, purposeful, and strategic use of speciﬁc nutritional interventions to enhance the adaptations targeted by individual exercise sessions or periodic training
plans, or to obtain other effects that will enhance performance in thelonger term (Jeukendrup, 2017a).” Athletics might be considered
the sport most suited to the application of periodized nutrition,
given the diversity of the bioenergetic and biomechanical demandsof the numerous different events. By extension, given the uniquedemands of all athletic disciplines and events, it is beyond the scopeof this review to highlight every potential nutrition periodization
approach. Instead, we will focus on a general framework highlighting the various considerations in the implementation of periodized
nutrition. This review will then highlight an emerging nutritional
periodization concept around the various approaches to carbohydrate (CHO) and fat periodization; from a macrocycle (weeks tomonths; e.g., chronic low-CHO high-fat [(LCHF]) to mesocycle(several days to weekly; e.g., high dietary to upregulate CHO
oxidation) and microcycle CHO periodization approaches
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Stellingwerff, Morton, and Burke(within day and between training session; e.g., acute CHOmanipulation).

Framework for Periodization of Nutrition

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The godfather of the American ﬁtness industry Jack Lalanne hasoften remarked, “Exercise is King while nutrition is Queen; put
them together and you have a Kingdom!” Of course, nutrition
strategies play a supportive role in enhancing acute training stimuli
into optimal training adaptation. For example, optimizing protein(PRO) intake, PRO quality, and timing achieves only a minor
adaptive hypertrophic response without the potent stimulus ofresistance exercise. However, nutrition serves an important function given that elite athletes have 1400–1800 eating occasions per
year, whereas training 300–800 times. Accordingly, Figure 1 highlights a theoretical framework that is fundamental for the prioritization and optimization of nutrition periodization that practitioners
can apply to a myriad of nutrition interventions. First, the coachand the entire support staff should have a full and comprehensive

understanding of the event-speciﬁc physiological, neuromuscular,
structural, and psychological determinants for success. Second, theperformance gaps of the individual athlete should be quantiﬁed as
best as possible against these performance determinants. From thisconstruct, the coach will strategically develop the various macro(months to years), meso- (weeks to months), and microcycles (daysto within days) aspects of training periodization and its speciﬁc
sessions, using these as to bridge between the goals and the gap.
Indeed, the integration of peer-reviewed evidence from training
studies with the tacit knowledge of elite coaches (Nash & Collins,2006) produces the “Science” and “Art” of elite training prescription and periodization (Kiely, 2012). The periodized training
schedule provides a framework for the sports nutrition professional
to match nutritional strategies to support training outcomes. Table 1
highlights the rationale involved in implementing macro-, meso-,
and microperiodized nutrition recommendations. Conversely,
Figure 1 outlines the process and highlights several periodized
nutrition examples, such as the macronutrient (CHO and PRO),micronutrient (iron), and ergogenic aid (creatine) examples ofmacro-, meso-, and microperiodization, respectively. However,

Figure 1 — A methodological framework required for successful nutrition periodization, including examples of macro- (months), meso- (weeks)
and microcycle (days/within day) nutrition periodization interventions for carbohydrate (CHO), protein (PRO), iron, and creatine. Dec = decreased; Inc =increased; GI = gastrointestinal.
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Table 1

Nutritional Considerations in Relation to Macro-, Meso- and Microcycle Training Periodization

Performance and/or periodization considerations

Nutritional context

Macroperiodization (months to weeks)
What is the speciﬁc load and density of this training phase/block forthis macrocycle (stimulus)?

What are the EA requirements of this macrophase?
In relation to the training phase/block, what are the current and longterm body composition goals? Are changes even necessary?
Are there any macro health considerations? (injury/illness proﬁle)Mesoperiodization (weeks to days)
What is the speciﬁc load and density of this training phase/block forthis mesocycle (stimulus)?

What are EA requirements of this mesophase?
If a competition block (many competitions over several days toweeks), what are the chronic to acute recovery requirements?

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What environmental training interventions are being implemented inthis phase?
Microperiodization (days to within day)What is the speciﬁc load and density of this training phase/block forthis microcycle (stimulus)?

What are the EA requirements of various different types of training
days?
What is the typical training day schedule? (within this speciﬁc training
block/phase)
What are the acute recovery requirements from a unique/speciﬁcsingle training session?
What are the acute recovery requirements from a single competition?

What are the training or competition speciﬁc interventions to optimize
performance? (from tapering to warm-up to sport psychology)

Estimation of required endogenous/exogenous substrates required
during this block should guide nutrition advice. Assessment of any
nutrition ergogenic aids that synergistically match themacroperiodization.
Ensure adequate EI for optimal EA. If required, assess RED-S statusindicators as outlined by Mountjoy et al. (2018).
Strategic team discussions around risk and reward to optimize bodycomposition targets, and develop an individual proﬁle.
Target potential nutrition interventions to individual athlete healthissues.
Estimation of required endogenous/exogenous substrates required due tothe speciﬁc training stimuli during this block should guide nutrition
advice. Consideration of any nutrition ergogenic aids that synergisticallymatch the mesoperiodization.
Ensure adequate EI for optimal EA. If required, assess RED-S statusindicators as outlined by Mountjoy et al. (2018).
During heavy competition phases, extensive logistical planning andpractice is required for general, competition, and recovery nutritioninterventions.
Environments (heat, cold, and altitude) dictate implementation ofvarious periodized nutrition interventions (e.g., hydration, iron, etc.).
Assessment of required endogenous/exogenous substrates required dueto the speciﬁc training stimuli during this block should guide nutrition
advice. Consideration of any nutrition ergogenic aids that synergisticallymatch the microperiodization.
Ensure adequate EI for optimal EA, appreciating that there may be
day-to-day EEE and EI variability.
Understanding the individual athletes daily and weekly schedule informs
micro (within hour) nutrition and supplement recommendations.
Estimation of exogenous/endogenous substrates required during individual training sessions, coupled with the training goals and phase, will
inform the pre-, during, and posttraining nutrition interventions.
Generally, all recovery interventions are optimized during rounds of acompetition, or throughout a competition, block to maximize subsequent
performance.
Competition phase tends to offer unique nutrition periodization challenges, such as body comp optimization during tapering, optimizing
recovery protocols, to acute competition speciﬁc ergogenic aids
(e.g., caffeine, sodium bicarbonate, etc.).

Note. EA = EI – EEE/fat-free mass. CHO = carbohydrate; EA = energy availability; EI = energy intake; EEE = exercise energy expenditure; RED-S = Relative Energy
Deﬁciency in Sport.

the narrative of this review will exclusively focus on energy and
CHO periodization.

Periodization of Energy Intake
Energy intake (EI) is a primary nutritional characteristic as it(a) establishes the baseline from which intakes of the macronutrients (including muscle substrates) are derived, (b) inﬂuences thecapacity of the diet to achieve micronutrient targets within nutrientdensity constraints, and (c) allows the manipulation of physique via
the interaction of training and energy balance. Given that theenergy cost of training is often the major determinant of an athlete’s

energy expenditure, and that the training load varies markedly
across micro-, meso-, and macrocycles of the training plan, EI
should also vary between days, weeks, and training phases.
In addition, some athletes may desire to manipulate their EIin attempts to alter physical and structural characteristics(e.g., reduce body fat or body mass and/or gain muscle mass),
but must appreciate the risks versus rewards of such manipulations.
Accordingly, energy manipulations should be strategically integrated into the annual plan to minimize the effects on training
quality or competition performance, and strategies should aim to
maintain sufﬁcient energy availability (EA) to reduce the acute andchronic issues associated with the development of Relative Energy

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Deﬁciency in Sport [RED-S; (Mountjoy et al., 2018)]. For a
speciﬁc review of low EA and RED-S in track and ﬁeld athletes,
the reader is referred to review by Melin et al. (2019) in the current
series.
To undertake periodization of EI, the nutrition professionaland coach need to undertake a full audit of step #3 (within Figure 1)of our framework through a nutrition lens. This assessment should
include estimations of total caloric and substrate utilization foreach unique type of workout, which then inﬂuences the ﬂuctuations or manipulations of energy and macronutrient intake thatneeds to be integrated into daily eating patterns, as well as anappreciation of these elements over a given training meso andmacrocycle. Many indirect protocols can be implemented toprovide information on energy expenditure of exercise (EEE)and fuel use; these include indirect calorimetry to estimate fuelutilization linked to internal load (e.g., heart rate) and/or externalload (e.g., running speed) and various technologies that canestimate caloric expenditures. It should be stressed, however,that accurate measurements of EI (Larson-Meyer et al., 2018)
and the EEE and activities of daily living (Murakami et al., 2016)
are extremely difﬁcult to make; indeed, daily mismatches of as
little as 300 kcal (1200 kJ; Torstveit et al., 2018), which are within
the typical errors of measurement of both EI and energy expenditure, can have profound effects on EA over the long term. In lightof current caution around the measurement or prescription of“optimal EA,” it is both unwise and impractical to suggest that
athletes should chronically “micromanage” the monitoring andmanipulation of EA or EI within training or competition environments. However, having an understanding of general needs andhow they ﬂuctuate can allow the athlete to develop behavioral
practices that allow EI to track with EEE (e.g., to consume
recovery snacks, or within session EI, on days or during periodsof higher EEE), and perhaps, to focus on energy goals during
targeted periods of body composition manipulation. The emerging
concept of periodization of body composition allows characteristics to be manipulated within an individualized range acrossdifferent phases of the annual plan according to short- and longterm issues of training adaptation, health, and performance(Heydenreich et al., 2017; Stellingwerff, 2018). A case study of a
9-year history of body composition management of an elite female
middle-distance runner (Stellingwerff, 2018) illustrates the gradual progression to optimal physique over the athlete’s career aswell as the manipulation within a season.

Carbohydrate and Fat Periodization
A key goal of training is to enhance the various metabolic pathways
to improve the capacity and/or rate of adenosine triphosphate(ATP) production, particularly to reduce or delay the onset offactors that may make these pathways limiting for competition
performance. Some of the principles by which these metabolic
pathways can be enhanced include increasing the size of the storage
and availability of endogenous fuels (capacity) and enhancing the
body’s ability to make use of exogenous fuels consumed just prior
to and during exercise (power). Further metabolic enhancement canalso occur by improving the delivery of nutrients and oxygen to theworking muscle, reducing the accumulation of by-products thatmight disturb cellular homeostasis or metabolic regulation, or
improving the efﬁciency (economy) of these pathways to produce
ATP across a range of absolute and relative exercise intensities.
Carefully organized dietary interventions to enhance the exercisenutrient interactions can augment the role that training alone alreadyprovides. The availability of modern laboratory technologies toinvestigate cellular signaling events over the past decade has
expanded insights into the role of nutritional support in promoting
adaptations to exercise. It is now known that many substrates, andin particular muscle glycogen and plasma free fatty acids, act not
only as fuels for the exercise bout being undertaken, but also as
regulators of the cellular and whole body adaptation to exercise,and speciﬁcally endurance exercise (Hansen et al., 2005; Hulston
et al., 2010; Morton et al., 2009; Yeo et al., 2008). In relation tothis, the reader is directed to a recent review in which a rangeof acute and chronically applied strategies to manipulate fat andCHO availability are deﬁned and explained, at least in relation toendurance events, to address some confusion over terminology,
application, and theoretical basis (Burke et al., 2018). This bodyof work was initially termed the “train-low (smart): competehigh” paradigm and involved the integration of reduced CHO
availability for carefully chosen training sessions to enhancemarkers of training adaptation, while approaching competition
with high CHO availability to maximize performance and recovery(Burke, 2010). More recently, the concept of periodization of CHO
availability has been explained using the theoretical model of“fueling for the work required” whereby CHO availability is
adjusted in accordance with the demands and goals of the speciﬁctraining session to be completed (Impey et al., 2018). With thisapproach, total daily CHO intake and its distribution over the day
can be modiﬁed day-by-day and meal-by-meal (i.e., within the
microcycle) to manipulate CHO availability for each exercise
occasion.

Strategies to Promote CHO Utilization During
Exercise
Carbohydrate, from muscle glycogen stores and plasma glucose,provides an effective and dominant fuel source for performanceacross a wide variety of events in athletics (Hawley & Leckey,2015). Indeed, it has been known for nearly a century that 100%
CHO produces ∼5.5% more ATP per liter of oxygen consumed
than compared with 100% fat oxidation (Krogh & Lindhard, 1920).
Therefore, the achievement of high CHO availability (deﬁned as
CHO stores available to provide the substrate needs of an event or
training session) is a key goal of competition nutrition and thereader is directed to reviews of the individualized competitionneeds across events in track and ﬁeld (Burke et al., 2019; Costa
et al., 2019; Slater et al., 2019; Stellingwerff et al., 2019; Sygoet al., 2019). In addition to promoting training quality, undertaking
sessions with high CHO availability can enhance the pathwaysof oxygen-independent glycolysis and CHO oxidation (Coxet al., 2010).

Promoting Training Adaptation via Low CHO
Availability
The rationale for deliberately promoting low CHO availability inrelation to a training session is that commencing and/or recoveringfrom a proportion of training sessions with reduced CHO availability activates acute cell signaling pathways that increase many of
the hallmark muscle adaptations to endurance training such as
mitochondrial biogenesis, angiogenesis and increased lipid oxidation (Figure 2). The landmark studies in the ﬁeld have typicallymanipulated preexercise muscle glycogen availability (Hansen
et al., 2005; Hulston et al., 2010; Morton et al., 2009; Yeo et al.,2008), given the rationale that glycogen concentration is a potent

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Figure 2 — Schematic overview of the potential cell signaling pathways regulating the enhanced mitochondrial adaptations associated with training
with low CHO availability. (1) Reduced muscle glycogen enhances both AMPK and p38MAPK phosphorylation that results in (2) activation andtranslocation of PGC-1α and p53 to the mitochondria and nucleus. (3) Upon entry into the nucleus, PGC-1α coactivates additional transcription factors(i.e., nuclear respiratory factor 1/2) to increase the expression of COX subunits and Tfam as well as autoregulating its own expression. In the mitochondria,
PGC-1α coactivates Tfam to coordinate regulation of mitochondrial DNA and induces expression of key mitochondrial proteins of the electron transport
chain, for example, COX subunits. Similar to PGC-1α, p53 also translocates to the mitochondria to modulate Tfam activity and mitochondrial DNA
expression and to the nucleus where it functions to increase expression of proteins involved in mitochondrial ﬁssion and fusion (Drp-1 and Mfn-2) andelectron transport chain protein proteins. (4) Exercising in conditions of reduced CHO availability increases adipose tissue and intramuscular lipolysis via
increased circulating adrenaline concentrations. (5) The resulting elevation in FFA activates the nuclear transcription factor, PPARδ to increase expressionof proteins involved in lipid metabolism such as CPT-1, PDK4, CD36, and HSL. (6) However, consuming preexercise meals rich in CHO and/or CHO
during exercise increases insulin, which can downregulate lipolysis thereby negating FFA mediated signaling. (7) In addition, CHO intake before or
during exercise can also reduce both AMPK and p38MAPK activity thus having negative implications for downstream regulators. AMPK = AMPactivated protein kinase; CHO = carbohydrate; COX = cytochrome c oxidase; CPT1 = carnitine palmitoyltransferase 1; Drp1 = dynamin-related protein 1;
FA = fatty acid; FFA = free fatty acid; FABP = fatty acid binding protein; Glu = glucose; HSL = hormone sensitive lipase; IMTG = intramusculartriglycerides; Mfn2 = mitofusion-2; p38MAPK = mitogen-activated protein kinase; PDK4 = pyruvate dehydrogenase kinase 4; PGC-1α = peroxisome
proliferator-activated receptor gamma coactivator 1-alpha; PPARδ = peroxisome proliferator-activated receptor; Tfam = mitochondrial transcription factor A.

regular of key cell signaling kinases (e.g., AMPK, p38), transcription factors (e.g., p53, PPAR) and transcriptional coactivators, forexample, PGC-1α (Bartlett et al., 2013; Hearris et al., 2018;
Psilander et al., 2013; Yeo et al., 2010). However, it is now
recognized that practical models of CHO periodization must extend
beyond just manipulating preexercise muscle glycogen availability. Accordingly, CHO availability is deﬁned as the sum of thecurrent individual endogenous (i.e., muscle and liver glycogen) andexogenous CHO (i.e., CHO consumed before and/or during exercise) that is available to sustain the required training or racing

intensity and duration (Impey et al., 2018). According to thisdeﬁnition, it is possible to have insufﬁcient CHO availability(even if exercise is commenced with high preexercise muscle
glycogen stores) if an inadequate dose of exogenous CHO is
consumed during prolonged exercise to sustain the desired intensity (Coyle et al., 1986). Alternatively, it is possible to commence
exercise with reduced muscle glycogen, but can still be considered
to have sufﬁcient CHO availability if the exogenous CHO consumed during exercise permits the completion of the desired
training intensity and duration (Widrick et al., 1993).

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Table 2 Overview of Practical Approaches to Manipulate Endogenous and Exogenous CHO Availability Within
CHO Periodization Strategies.
Practical approach

Practical implementation/theoretical rationale

Supporting references

Train low (glycogen)session• Both muscle and liver glycogen are reduced during an initial morning

Hulston et al. (2010); Morton et al.
(2009); Yeo et al. (2010, 2008)

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Train low (fasted)sessionRecovery low/sleep low
strategy

Train high (glycogen +exogenous CHO)
sessionAmalgamation of targeted CHO availability
training and recovery
approaches

training session. CHO intake is then withheld in recovery or suboptimal
intakes occur such that a second session is completed in the afternoon or
early evening with reduced preexercise CHO availability. Depending on
the timing of both sessions, the total time considered in a state of low CHO
availability could range from 3 to 8 hr.
• Commencing exercise with low muscle glycogen stores and/or sustaining
exercise intensity and/or duration to a speciﬁc level of absolute glycogendepletion is associated with the activation of key cell signaling proteins(e.g., AMPK, p38, PPAR, PGC-1α), which achieve a coordinated upregulation of the nuclear and mitochondrial genomes. Over a chronic training
period, this may increase oxidative enzyme protein content/activity,
upregulate whole body and intramuscular lipid metabolism, with potential
improvements in exercise performance and capacity.
• Breakfast is consumed after training and no form of CHO is consumed
during exercise resulting in signiﬁcant elevated FFAs. This approach
would predominantly target reduced liver glycogen (associated withfasting in the overnight period) though depending on the CHO intake
consumed in the recovery period after the last training session, pretraining
muscle glycogen may also be considered low.
• Exercise undertaken in fasted conditions leads to increased metabolic stressfor the muscle, central nervous system, and/or liver gluconeogenesis andleads to upregulation of AMPK and signaling pathways that increase
expression of proteins regulating substrate transport (e.g., GLUT4 andCD36, FABPm, respectively) and substrate utilization (e.g., PDK4, HK,CS, β-HAD).
• Both muscle and liver glycogen are reduced during an evening training
session. CHO intake is then withheld in recovery or suboptimal intakes
occur such that a second session is completed on the subsequent morningwith reduced preexercise CHO availability. Depending on the timing ofboth sessions, the total time considered in a state of low CHO availability
could range from 8 to 14 hr.
• Restricting CHO intake in the postexercise period, therefore, maintains
postexercise muscle and liver glycogen at reduced levels as well as
prolongs the duration of postexercise elevations in circulating FFA
availability. The interactive effects of changes in substrate availability may
sustain the postexercise upregulation of cell signaling (e.g., AMPK, p53,
PGC-1α) pathways thus leading to increases in the adaptive response to thesession. The sleep-low train low model has been associated with improved
exercise performance in trained triathletes.
• Training sessions deliberately commenced with high muscle and liver
glycogen following optimal pretraining (e.g., CHO “loading” of 6–12 g/kg
body mass, pretraining meal of 1–3 g/kg body mass) and in-training
fueling (e.g., CHO consumed during exercise at a rate of 30–90 g per hour).
• In this approach, promotion of high training intensity, duration, training of
the gut, and practicing in competition fueling are the goals.
• The above approaches are deliberately amalgamated over a 24- to 48-hr
period. In this model, an initial train high session may be completed topromote training intensity and duration followed by a second train low
session that is performed 24–48 hr later with reduced CHO availability.
The second session may have arisen as a result of a combination of sleeplow, recover low, and a low daily absolute CHO intake.
• Using this model, CHO availability can be adjusted, before, during, and/or
after each training session in an attempt to take advantage of the cellularsignaling responses that may occur with CHO restriction at each of thesetime periods.

Akerstrom et al. (2006); De Bock et al.
(2008); Van Proeyen et al. (2011)

Bartlett et al. (2013); Marquet et al.
(2016); Pilegaard et al. (2005)

Costa et al. (2017); Cox et al. (2010)

Impey et al. (2018); Stellingwerff(2012)

Note. For a summary of the terminology and rationale of different strategies of periodized fuel support for training and competition, see Burke et al. (2018) while theprinciples underpinning skeletal muscle adaptations, training, and performance outcomes are detailed in the review of Impey et al. (2018). AMPK = AMP-activated protein
kinase; B-HAD = beta hydroxyacyl-Coenzyme A dehydrogenase; CD 36 = cluster of differentiation fatty acid transporter; CHO = carbohydrate; CS = citrate synthase;
FABPm = muscle fatty acid binding protein; FFA = free fatty acids; GLUT4 = glucose transporter 4; HK = hexokinase; PGC = peroxisome proliferator-activated receptor
gamma coactivator; PPARδ = peroxisome proliferator-activated receptor; PDK4 = pyruvate dehydrogenase kinase 4; p38 = mitogen-activated protein kinases.

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Figure 3 — Supplement individualization and piloting framework, including potential data collection variables to help inform protocol and efﬁcacy.
GI = gastrointestinal; RPE = ratings of perceived exertion.

The various main approaches to manipulating CHO availability in relation to training are presented in Table 2. Essentially, it is
now recognized that manipulation of both endogenous and exogenous CHO availability before (Hansen et al., 2005; Yeo et al.,2008), during (Akerstrom et al., 2006; Morton et al., 2009), andafter training sessions (Marquet et al., 2016; Pilegaard et al., 2005)
may lead to an augmented training response; at least in terms ofacute (e.g., cell signaling) and chronic (e.g., changes in enzyme
protein content and activity) skeletal muscle metabolic adaptations(Figure 2). Despite the theoretical rationale for incorporating aperiodization of CHO availability into an elite athlete’s training
program, balancing the risk versus reward can be challenging for anumber of reasons. First, the majority of studies to date have been
conducted using cycling-based or knee extensor exercise models(78% of 27 studies; Impey et al., 2018). These modalities may morenaturally lend themselves to train-low sessions given the nonweight-bearing activity and lower eccentric loading compared withrunning. Second, the CHO requirements of the typical training
sessions undertaken by elite track and ﬁeld athletes are not wellknown and practitioners must use theoretical knowledge of glycogen utilization from relevant laboratory and ﬁeld-based studies toorganize appropriate manipulation of training and diet. A recent
meta-analysis which provides more information in this regard
clearly highlights the impact of intensity and duration on glycogenuse (Areta & Hopkins, 2018), but practitioners need to consider theuse of the internal and external training load metrics outlined in
Figure 3, to make best estimates. Of particular note to track andﬁeld athletes are the negative effects of reduced CHO (and energy)
availability on markers of bone turnover (Sale et al., 2015), which
contrast with the beneﬁts of immediate postexercise feeding of
CHO and PRO (Townsend et al., 2017). Although this needs to be
conﬁrmed in a longitudinal model, prolonged periods of training
with reduced CHO availability may potentially increase the risk forstress fractures, in runners who are already at risk for RED-S andstress fractures (Heikura et al., 2018). Indeed, low CHO availability

may mediate disturbed reproductive function in its own right(Loucks, 2014), creating another pathway to explain the increasein musculoskeletal injuries seen with low EA (Rauh et al., 2014).
Similarly, reduced CHO availability during training may lead toincreased susceptibility to illness owing to the role of CHO in
modulating postexercise immune responses (Costa et al., 2005).
Finally, evidence that the improved metabolic adaptations associated with the periodization of low CHO availability within an
athlete’s training program actually translates to improved performance outcomes is equivocal. Indeed, Impey et al. (2018) reported
that, although periodically completing endurance-training sessions(e.g., 30–50% of training sessions) with reduced CHO availability
modulates the activation of acute cell signaling pathways (73%of n = 11 studies) and oxidative skeletal muscle adaptations (78%of n = 9), only 37% of studies demonstrate improvements inperformance.
The development of practical approaches to sport-speciﬁc
CHO periodization requires consideration of the individual athlete’s training (e.g., intensity, duration, body composition, altitude,
ambient temperature, etc.) and competitive goals (e.g., timerequired to attain and taper for peak performance) within thespeciﬁc micro-, meso-, and macrocycle. An illustration of theimplementation of periodized CHO availability in the real world
was provided by a 16-week case study of three elite marathon
runners (Stellingwerff, 2012). These athletes undertook a weekly
average of 2.5 sessions involving low CHO availability during
the ﬁrst 12 weeks. However, during the subsequent 4-week period
which focused on competition preparation, nutritional strategies
shifted toward an increased frequency of practicing CHO fueling
during training sessions (2.5 sessions per week), coupled with areduction in low CHO training sessions (Stellingwerff, 2012). In
this study, with regard to training with low CHO availability, fasted
training was reported to be physiologically and psychologically“easier” to integrate than the more strenuous low muscle glycogentraining sessions. Regardless of the speciﬁc approach, it is intuitive

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to avoid chronic periods (>3–5 days), or consecutive performance,of the various “train-low” modalities due to the potential negative
effects of both low CHO and inadequate total EA on training
quality, competitive performance and health outcomes (Burkeet al., 2017; Havemann et al., 2006; Mujika, 2018). Rather, careful
day-to-day periodization is likely to maintain metabolic ﬂexibility
and still allow the completion of high-intensity and prolonged
duration workloads on heavy training days. Intuitively, train-low
may be best left to those training sessions that are not as CHO
dependent and where the intensity and duration is not likely to becompromised by reduced CHO availability (e.g., steady-state typetraining sessions performed at intensities below the lactate threshold); however, signiﬁcant work remains on how to best periodize
CHO with the numerous training permutations (Table 2). As withall nutritional strategies, application of CHO periodization should
only be done in conjunction with appropriately qualiﬁed nutrition
professionals and be continually reﬁned and optimized.

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Fat: a Relatively Unlimited Fuel Source and Driverof Adaptation
Although endurance-trained athletes have an enhanced capacity forfat oxidation compared with untrained, this adaptation is clearly not
maximized from training alone as it can be doubled, or even tripled,by chronic adaptation to a LCHF diet (Burke et al., 2002, 2017;
Carey et al., 2001). Various models have been used to achieve thesehigh fat oxidation rates including nonketogenic CHO-restricteddiet (NK-LCHF; typically 65% energy as fat and <20% energy
from CHO to prevent ketosis while reducing CHO intake to levels
below the fuel costs of daily training) and the more restrictive
ketogenic LCHF diet (K-LCHF: typically <50 g/day CHO and
75–80% fat; Burke et al., 2018). However, studies have shown thatas little as 5 days of exposure to HFLC diets, while continuing toundertake both high volume and intensity of training, achieves arobust retooling of the muscle to increase intramuscular triglycerides stores, and enhance the mobilization, transport, uptake, andoxidation of fats (for review see Burke, 2015).
By itself, however, chronic adaptation to a NK-LCHF does nottranslate into clear improvements in endurance performance,
except in speciﬁc scenarios or individuals (Burke, 2015). Therefore, a microperiodization protocol which (theoretically) could
sequentially enhance the capacity of both fat- and CHO-based
fuel oxidation prior to an endurance event has been proposed; thisinvolves a 5–6 days fat adaptation phase followed by acuterestoration of CHO availability just prior to and during the endurance task (Burke et al., 2002; Carey et al., 2001; Havemann et al.,2006). Investigation of this protocol showed that the muscle
retooling achieved by the fat-adaptation phase is robust in continuing to promote higher rates of fat oxidation in the face of aggressive
strategies to restore high CHO availability during the endurance
task (Burke et al., 2002; Carey et al., 2001). Despite substantiallyreduced rates of muscle glycogen utilization during the early part ofthe exercise task, there was no clear enhancement of a subsequent
time trial in any of these studies. One apparent explanation for thisoutcome is that, rather than sparing glycogen utilization, chronic
exposure to a high-fat diet causes an impairment of CHO oxidation
during exercise due to a reduction on glycogenolysis and a downregulation of the activity of the pyruvate dehydrogenase complex[PDH; (Stellingwerff et al., 2006)]. Data from rodent models
suggests that such inhibition of PDH activity may actually be
due to the effects of reduced muscle glycogen availability. Indeed,
commencing exercise with reduced muscle glycogen augments

the activation of peroxisome proliferator-activated receptor-δ(PPAR-δ; Philp et al., 2013), a transcription factor that upregulates
pyruvate dehydrogenase kinase 4 (PDK4) that, in turn, phosphorylates and inactivates PDH. In human muscle, however, we haverecently shown that the downregulation of CHO metabolism
appears to be a consequence of the high-fat diet and increased
fat availability rather than CHO restriction alone (Leckey et al.,2018). The consequences of reduced CHO utilization within thetricarboxylic acid cycle are likely to manifest in a reduced capacity
for ATP production at high intensities. For example, in a study inwhich the fat adaptation-CHO restoration model was undertaken
prior to a 100 km cycling time trial, there was a trend toward
impairment of overall performance, but a signiﬁcant reduction inability to complete 1-km and 4-km sprints undertaken at ∼90%
peak power output interspersed within the protocol (Havemannet al., 2006). This reduction in power output matches the ∼30%
reduction in PDH and estimated glycogenolysis during a 1-min
sprint at 150% of peak power output found by Stellingwerff
et al. (2006).
The proposed beneﬁts of chronic adaptation to ketogenic
LCHF diets has also received recent attention in both the lay(Brukner, 2013) and the scientiﬁc press (Noakes et al., 2014; Volek
et al., 2015) due to the proposed beneﬁts of increased fat oxidationand exposure to high levels of circulating ketone bodies. Indeed, anearly study featuring 4 weeks of LCHF adaptation to such CHO
restriction showed the muscle’s plasticity in being able to increase
fat utilization to maintain exercise capacity at modest power outputs (∼60% VO2max; Phinney et al., 1983). However, Phinney
et al. already noted that this feat was achieved in the face ofimpairments of capacity to undertake exercise at higher intensities.
A more recent investigation of 3.5 weeks of exposure to a K-LCHF
diet in elite race walkers demonstrated an apparent rationale forPhinney et al.’s ﬁndings (Burke et al., 2017). In this study, some ofthe highest rates for fat oxidation ever reported in the literature wereachieved following adaptation to the K-LCHF diet, under conditions of either fasting or intake of fat during a prolonged exercise
protocol. However, this was associated with an increase in theoxygen cost (i.e., reduced economy) of walking at a range of speeds
relevant to the competitive events in this discipline (20 and 50 km),and the K-LCHF diet did not improve 10,000 m performancecompared with the CHO-supported dietary groups (Burke et al.,2017).
Taken together, chronic LCHF interventions have been shown
to (a) decrease CHO oxidation (Burke et al., 2002; Carey et al.,
2001; Havemann et al., 2006) via decreased glycogen utilization
and PDH activation (Stellingwerff et al., 2006), (b) result in
decreased exercise economy due to lower ATP production associated with increased fat oxidation (Burke et al., 2017), and(c) probably cause a decrease of the intestinal glucose transport
proteins (SGLT-1) reducing the capacity for intestinal absorption.
This would decrease the effectiveness of CHO feeding strategies,
thus increasing the risk of gut disturbances (Jeukendrup, 2017b).
It is important that coaches and athletes understand the metabolic
demands and limiting factors in their events (Figure 1), andtrial-speciﬁc interventions on an individual level (Figure 3), andrealize that all sustained majority of track and ﬁeld events are
exceptionally CHO dependent. Indeed, there is continued interest
in increasing rather than decreasing CHO dependence to improve
performance of events of sustained high-intensity exercise atintensities around the “lactate threshold” (e.g., the marathon) totake advantage of the greater economy of ATP production from theoxidation of this fuel (Burke et al., 2019).

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Conclusions and Future Directions
The numerous various events in athletics, all with unique bioenergetics, biomechanical, and structural performance determinants,
lend themselves to endless permutations of potential periodized
nutrition interventions. Therefore, this review took a holistic
approach to develop a nutrition periodization framework to guidepractitioners in the ﬁeld across these nutrition periodization options, while grounding them in targeted intervention ﬁrst principles(Figure 1 and Table 1). From this framework, the literature has
been examined regarding macro-, meso-, and microperiodization of
CHO availability, and consequently, fat periodization (Table 2 andFigure 2), with considerations and recommendations to individualize and test in the ﬁeld, as required (Figure 3). Obviously, thispaper just focused on an example of nutrition periodization by
examining the research in the macro-, meso-, and/or micromanipulating of CHO, and by extension. However, Figure 1 highlights
various other nutrition examples of periodization that are beyond
the scope of this review, but we would highlight a few other papers
in this series that also feature periodized nutrition examples forprotein (Witard et al., 2019), supplements (Peeling et al., 2019),
CHO fueling (Burke et al., 2019), and middle-distance athletes(Stellingwerff et al., 2018). With an appreciation of the complexities of training periodization, future directions in this ﬁeld should
include better quantiﬁcation of knowledge and application ofexisting periodized approaches in elite athletes, as well as systematically controlled CHO periodization approaches over prolonged
training blocks in larger cohorts of athletes. Other scientiﬁc areas
for future investigation also include the meso and/or macroperiodization of ergogenic aids in attempts to enhance training adaptations and performance. In summary, the ﬁeld of periodized
nutrition has made considerable gains over the last decade, but
is ripe for further progress.

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