Sports Foods and Dietary Supplements for Optimal Function
and Performance Enhancement in Track-and-Field Athletes
Peter Peeling
The University of Western Australia and Western Australian Institute of Sport
Linda M. Castell
University of Oxford
Wim Derave
Ghent University
Olivier de Hon
Anti-Doping Authority Netherlands
Louise M. Burke
Australian Institute of Sport and Australian Catholic University
Athletes are exposed to numerous nutritional products, attractively marketed with claims of optimizing health, function, and
performance. However, there is limited evidence to support many of these claims, and the efficacy and safety of many products is
questionable. The variety of nutritional aids considered for use by track-and-field athletes includes sports foods, performance
supplements, and therapeutic nutritional aids. Support for sports foods and five evidence-based performance supplements
(caffeine, creatine, nitrate/beetroot juice, β-alanine, and bicarbonate) varies according to the event, the specific scenario of use,
and the individual athlete’s goals and responsiveness. Specific challenges include developing protocols to manage repeated use of
performance supplements in multievent or heat-final competitions or the interaction between several products which are used
concurrently. Potential disadvantages of supplement use include expense, false expectancy, and the risk of ingesting banned
substances sometimes present as contaminants. However, a pragmatic approach to the decision-making process for supplement
use is recommended. The authors conclude that it is pertinent for sports foods and nutritional supplements to be considered only
where a strong evidence base supports their use as safe, legal, and effective and that such supplements are trialed thoroughly by
the individual before committing to use in a competition setting.
Keywords: ergogenic aids, performance nutrition, high performance, athletics
Numerous nutritional products are marketed with claims of
optimizing athlete health and function and/or enhancing performance.
Products that fall under the banner of “Sports Foods” or “Dietary
Supplements,” may be used to support performance during training
and competition or for enhancing aspects of training adaptation,
recovery, immune function, and/or overall athlete health. Effective
marketing campaigns and athlete endorsements may convince us that
certain sports foods and supplements are fundamental in allowing
athletes to reach their sporting goals. However, this approach is naive
in understanding the true foundations of athlete success, such as the
inherent genetic predisposition for athletic characteristics, the many
hours of well-structured/periodized training, appropriate underlying
nutrition, adequate sleep and recovery, and of course, good overall
physical and mental health. Nevertheless, if these variables are all
accounted for, there may be a role for sports foods and dietary
supplements in an athlete’s training and competition routine, particularly
within elite sport where marginal performance gains are pursued.
The following review presents general considerations for track-andfield
athletes using sports foods and dietary supplements to enhance
performance, in addition to exploring the potential therapeutic/
prophylactic use of these nutritional aids.
Definition of a Dietary Supplement
Maughan et al. (2018a) recently defined a dietary supplement as:
A food, food component, nutrient, or non-food compound that
is purposefully ingested in addition to the habitually consumed
diet with the aim of achieving a specific health and/or performance
benefit.
Prevalence
A recent systematic review and meta-analysis of 159 unique studies
in athlete populations (Knapik et al., 2016) investigated the
prevalence of dietary supplement use (defined using the Federal
Drug Administration’s Dietary Supplement Health and Education
Act of 1994; e.g., sports foods, iron, vitamins, etc.) by sport, sex,
and athlete status (i.e., elite vs. nonelite). High variability in
supplement use among various sporting groups was reported,
Peeling is with School of Human Sciences (Exercise and Sport Science), The University
of Western Australia, Crawley, Western Australia, Australia; and the Western Australian
Institute of Sport, Mt Claremont, Western Australia, Australia. Castell is with Green
Templeton College, University of Oxford, Oxford, United Kingdom. Derave is with the
Dept. of Movement and Sports Sciences, Ghent University, Ghent, Belgium. de Hon is
with the Anti-Doping Authority Netherlands, Capelle aan den IJssel, The Netherlands.
Burke is with the Australian Institute of Sport, Bruce, Australian Capital Territory,
Australia; and the Mary MacKillop Institute for Health Research, Australian Catholic
University, Melbourne, Victoria, Australia. Address author correspondence to Peter
Peeling at peter.peeling@uwa.edu.au.
198
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https://doi.org/10.1123/ijsnem.2018-0271
© 2019 Human Kinetics, Inc. SCHOLARLY REVIEW
with the combined group summary prevalence estimate (SPE)
ranging from 4 to 62% across various supplement types. When
differentiated by athlete status, results showed that elite athlete
cohorts (SPE male: ∼69% and SPE female: ∼71%) presented with
greater rates of supplement use than their nonelite counterparts
(SPE male: ∼48% and SPE female: ∼42%). Furthermore, sex
differences were apparent, with greater use of supplemental iron
reported by female athletes, whereas males used products such as
protein, creatine, and vitamin E more often. Although specific
supplement use among athlete groups is hard to quantify, these
outcomes suggest that service providers (i.e., dietitians, physiologists,
sports physicians) working with athlete cohorts should
be aware of differences in the incidence and type of supplement
use within a given group of athletes, with caliber and sex being
discriminating characteristics. For further insights into the prevalence
and rationale for use of supplements and sports foods, the
reader is directed to recent comprehensive review of the topic
(Garthe & Maughan, 2018).
Sports Foods
The term “Sports Foods” generally refers to specifically formulated
food products that are commercially developed for use by athletes.
The various categories of such foods are outlined in Table 1, with a
specific function to target nutritional goals that underpin training
adaptation, recovery, and competition performance (Burke & Cato,
2015). Although they often contain nutrients in similar amounts to
those found in whole foods and manufactured products in the
general food supply (hereafter, called “everyday foods”), sports
foods may offer the practical advantage of combining all the
nutrients needed for a specific goal in a single source. In addition,
the use of novel food and packaging technology can make sports
foods easy to transport, store hygienically, prepare, and consume,
particularly in situations before, during, or after/between competition
events and training sessions. However, although some sports
foods resemble “everyday food,” they also differ in that they may
consist of only a few nutrients compared with the many hundreds of
nutrients and phytochemicals found in the former. For that reason,
sports foods should not be used as a dietary replacement for
athletes, but rather as a supplementary strategy on occasions where
a specific combination of key nutrients is required.
The ergogenic properties of sports foods, in general, can be
ascribed to four main physiological goals, which they help to
support:
a. Hydration: Fluid ingestion for maintaining or restoring hydration
status.
b. Fuelling: Carbohydrate provision before, during, and following/
between exercise.
c. Anabolism: Protein ingestion to promote amino acid delivery
for optimal training adaptation and event recovery.
d. Osmolality: Electrolyte ingestion to replenish loss in sweat.
These goals are generally accepted by the broad sport nutrition
scientific community as being determinants of sports performance
and training response. Of note, the risk of dehydration and fuel/
electrolyte depletion is predominately an issue during longer athletic
events, such as distance running and race walking; furthermore, there
is ample evidence of the benefits of hydration, carbohydrate fueling,
and electrolyte replacements during these events (Burke, 2010;
Hoffman et al., 2018). Alternatively, athletic sprint events require
a high level of muscle power, and their training-induced muscle
hypertrophy relies on adequate protein and amino acids provision
around training sessions (Reidy & Rasmussen, 2016). Each sports
foods category will contribute to one or more of these physiological
goals, yet each in a variable degree. The link between the sports
foods categories and their respective goals is summarized in Table 1.
Table 1 Summary of the Roles and Ingredients in Sports Foods
Active ingredient Water Carbohydrates Protein Electrolytes
Product Physiological goal Hydration Fueling Anabolism Osmolality
Isotonic sports drink ✓✓ ✓ ✓
High-energy sports drink ✓ ✓✓ ✓
Electrolyte supplement (drink form) ✓ ✓✓
Sports gel ✓✓
Protein supplement (drink form) ✓ ✓ ✓✓ ✓
Sports bars ✓ ✓ ✓
Sports confectionary ✓✓
Liquid meal supplements ✓ ✓✓ ✓ ✓
Advantages of sports foods • Sports foods can contain only those ingredients that are actually needed during exercise.
Foods in the general food supply, particularly whole foods, will usually contain other
nutrients, such as fat and fibers, which are not needed during a race, and may cause
gastrointestinal discomfort.
• Sports foods may be manufactured to optimize serving size, convenience, digestibility,
storage, and transport.
Concerns about sports foods • Sports foods are more expensive than “everyday foods” and may drain an unnecessarily
large share of the athlete’s budget. It should be noted that many sports nutrition goals can
easily be met with the use of everyday foods. A typical example is the protein-rich recovery
drinks that can be adequately replaced by the much cheaper dairy products (e.g., skim milk or
yogurt).
• An overreliance on sports foods as energy sources may lead to poor nutrient intake and
limited dietary variety.
✓ Can contribute to this goal. ✓✓ Is an important contributor to this goal.
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Of course, manufacturers want to claim additional benefits of
their specific products and proprietary blends, which usually lack
any scientific substantiation, beyond the benefits of each compound
in isolation. Of note, some manufacturers add performance supplements
or other ingredients to sports foods. For instance, protein
shakes can contain creatine, sport drinks or sports bars can contain
caffeine, and vitamins can be found in the most unexpected places
(e.g., in the so-called “sports/fitness waters” that provide a pleasant
tasting drink rather than addressing any unique athlete need). This
makes the distinction between sports foods and sports supplements
more diffuse, and it also greatly complicates the work of sport
nutritionists to keep track of the total daily doses of supplements
and micronutrients to which athletes are exposed. To track the total
ingestion of such ingredients and to reduce concerns around
product contamination via raw ingredients that may be considered
at higher risk of this problem, athletes are guided to choose brands
of sports foods with the simplest formulations to meet the specific
goals for which they are designed; in general, they should focus
their use of performance supplements to separate protocols, using
separate products, which have preferably been third-party batch
tested or are manufactured by large (reputable) food companies.
The exception to this might be caffeine, which already has a
crossover to the food industry, as it is found in the athlete’s diet
via their intake of “everyday-consumer” products, such as coffee,
tea, iced coffee beverages, and “energy drinks.”.
In summary, sports foods may provide a valuable contribution
to an athlete’s nutrition plan, providing nutrients that support
training adaptation (e.g., protein) and promote performance (e.g.,
carbohydrate and fluid/electrolytes). However, their role should not
be overestimated, as many of those goals can, to a large extent, be
also obtained by carefully selected “everyday” foods.
Performance Supplements
Although countless supplements are marketed with the claims of
directly enhancing athletic performance, only a handful are supported
by an evidence base that warrants consideration for trial use
by athletes (see Figure 1 relevant to the decision-making process).
A recent review of this area categorizes the commonly encountered
performance supplements in terms of their research support and
level of efficacy (Peeling et al., 2018). In addition, the recent
International Olympic Committee consensus statement on supplement
use by high-performance athletes (Maughan et al., 2018a)
proposes that only five performance supplements have an adequate
level of evidence to suggest marginal performance gains may be
possible for elite athletes (a population where such gains are
generally harder to obtain) when added to a bespoke and periodized
training and nutrition plan. These supplements are summarized
with the mechanism of action and the potential application to trackand-field
athletics presented in Tables 2 and 3, respectively.
Caffeine
Caffeine shows well-established benefits for enhancing athletic
performance across both endurance-based events and short-term,
supramaximal tasks. Caffeine dosages of 3–6 mg/kg of body mass
(BM), consumed ∼60 min prior to exercise in the form of anhydrous
caffeine (i.e., pill or powder form), are commonly shown to
result in performance gains (Ganio et al., 2009). However, lower
caffeine doses (<3 mg/kg BM, ∼200 mg), provided both before and
during exercise, have also resulted in an ergogenic benefit (Spriet,
2014). Of note, recent research has suggested that the ergogenic
effects of caffeine are influenced by the athlete’s variant of a
number of genes, including the CYP1A2 gene involved in the
liver metabolism of caffeine (Guest et al., 2018). This explains the
well-known variability in individual responses to the “social” use
of caffeine, confirming the need for athletes both to trial their
intended performance uses of caffeine prior to implementation in
competition and to take into account their personal history of
reactions to caffeine intake in “everyday life” (e.g., effects on
heart rate, jitteriness, or sleep quality). Interestingly, larger caffeine
doses (≥9 mg/kg BM) do not appear to increase the performance
effect (Bruce et al., 2000), and are more likely to increase the risk
of negative side effects such as nausea, anxiousness, insomnia,
and restlessness (Burke, 2008). Caffeine habituation seems to have
limited impact on the performance effects of this stimulant
(Goldstein et al., 2010); high-habitual daily caffeine users tend
to encounter similar performance benefits as those with low and
moderate intakes (Gonçalves et al., 2017). Furthermore, studies
have shown that athletes need not undertake “caffeine withdrawal”
over the days prior to competition use to achieve a performance
improvement (Irwin et al., 2011). Earlier studies that suggested a
larger performance improvement when caffeine supplementation
was preceded by a dehabituation period may have been measuring
the reversal of the negative effects of caffeine withdrawal
(i.e., headache, fatigue, demotivation; Irwin et al., 2011) on top
of the normal performance effect rather than a unique benefit.
The caffeine supplementation literature shows strong evidence
of improved performance when it is consumed before events
varying in duration from 5 to 150 min (Ganio et al., 2009).
Furthermore, low–moderate doses of caffeine (100–300 mg) consumed
during endurance exercise (after 15–80 min of activity)
have also been shown to enhance endurance performance by a
range of 3–7% (Paton et al., 2015; Talanian & Spriet, 2016). When
considering short-term, supramaximal tasks, the ingestion of
3–6 mg/kg BM of caffeine taken 50–60 min preexercise relates
to performance gains of >3% for anaerobic activities of 1–2 min in
duration (Wiles et al., 2006). Therefore, there is support for highperformance
track-and-field athletes in the longer sprints, middle
distance, and endurance/ultraendurance events to consider competition
use of caffeine. Furthermore, shifting the “social” intake of
caffeine to target its effects to training sessions may help to
improve the quality of some workouts, particularly if rehearsing
competition practices or undertaking sessions in a fuel-depleted
state (Lane et al., 2013).
Creatine Monohydrate
Creatine monohydrate (CM) supplementation increases muscle
creatine and phosphocreatine stores, sustaining exercise that is
otherwise limited by the inability of phosphocreatine resynthesis to
keep pace with exercise fuel demands, for example, single and
repeated bouts of high-intensity exercise (<150 s duration), with the
most pronounced effects evident during tasks <30 s (Branch, 2003;
Lanhers et al., 2017). Indeed, creatine supplementation received
widespread attention in 1992 when the first report on successful
loading protocols (Harris et al., 1992) was published at the same
time as anecdotes emerged from the Barcelona Olympic Games
regarding its use by gold-medal winning British track-and-field
sprinters. In addition, chronic training adaptations, such as lean
mass gains and improvements to muscular strength and power,
have also been noted with both direct and indirect mechanisms
proposed (Table 2). Less commonly, performance advantages for
endurance athletes have also been suggested, including such
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Figure 1 — A pragmatic approach to making decisions about supplement use to optimize function and performance in athletes. Adapted from “IOC
consensus statement: Dietary supplements and the high-performance athlete,” by R. J. Maughan, L. M. Burke, J. Dvorak, D. E. Larson-Meyer, P. Peeling,
S. M. Phillips, : : : L. Engebretsen, 2018a, International Journal of Sport Nutrition and Exercise Metabolism, 28(2), pp. 104–125.
IJSNEM Vol. 29, No. 2, 2019 201
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benefits as enhanced glycogen storage and thermoregulation secondary
to the changes in the cellular environment associated with
the additional storage of creatine and water (Cooper et al., 2012;
Kreider et al., 2017); however, the potential negative influence of
minor weight gain from such mechanisms should be considered in
the context of event-specific performance requirements (see Table 2).
Effective supplementation protocols generally encompass a
“loading phase” of ∼20 g/day (divided into 4 equal 5 g doses/day),
for 5–7 days, followed by a “maintenance phase,” typically
involving a single daily CM dose of 3–5 g for the duration of
the supplementation period (Hultman et al., 1996). Alternative
approaches propose lower doses of CM (2–5 g/day), consumed for
approximately 4 weeks (Rawson et al., 2011), based on the concept
that low doses of CM provided over an adequate time period can
increase muscle creatine levels (Hultman et al., 1996). Of note,
consuming CM concurrently with a mixed protein/carbohydrate
source (∼50 g of protein and carbohydrate) may enhance muscle
creatine uptake via insulin stimulation (Steenge et al., 2000), while
it takes ∼4–6 weeks following the cessation of supplementation for
muscle stores to return to baseline levels.
No negative health effects have been noted with the long-term
use of CM (up to 4 years) when appropriate loading protocols are
followed (Schilling et al., 2001), and in some instances, potential
anti-inflammatory effects are proposed (Deminice et al., 2013).
Therefore, creatine supplementation consumed according to the
previously mentioned protocols shows strong efficacy for both
Table 2 Roles and Challenges of Evidence-Based Performance Supplements
Supplement Mechanism of action
Challenges around use in track-and-field events
(Burke, 2017)
Caffeine Caffeine acts as an adenosine receptor antagonist, with many
effects on different organs and systems. Actions include increases
in epinephrine release, improvements in neuromuscular function,
vigilance and alertness, and a masking of pain and perception of
effort during exercise (Burke, 2008; Spriet, 2014).
• High degree of individual variability includes potential for negative
response, minimal response, positive response, and super response;
thorough practice is needed.
• Repeated use for events within the same day (e.g., heptathlon and
decathlon) requires careful planning of the timing and amount of
doses, including whether a top up dose is even needed.
• Use on successive days (e.g., heats and finals of many events in
major meets) requires consideration of the effect on sleep and
overall recovery, especially when the first event has a late-night
schedule.
• Interactions with the efficacy or side effects of other supplements
used concurrently needs careful consideration and experimentation;
this is a likely scenario in many events (see Table 3).
Creatine
monohydrate
Supplementation with creatine monohydrate increases muscle
creatine stores and augments the rate of PCr resynthesis,
thereby enhancing short-term, high-intensity exercise capacity
(Buford et al., 2007) and the ability to perform repeat highintensity
bouts. Chronic effects of increased muscle size and
strength might be explained by indirect benefits (allowing the
athlete to train harder) as well as the direct benefits of
upregulation of cellular signaling and protein synthesis due to
changes in cellular osmolality (Safdar et al., 2008). Benefits of
additional muscle storage of glycogen and water might be of
interest to endurance events (Twycross-Lewis et al., 2016).
• Weight gain of 1–2 kg associated with creatine supplementation
(Buford et al., 2007) may be counterproductive for weight-sensitive
events, such as jumps and distance races. However, a low-dose
approach that avoids the CM “loading phase” may avoid such
issues (Rawson et al., 2011).
• Interactions with the efficacy or side effects of other supplements
used concurrently needs careful consideration and experimentation
(see Table 3). Indeed, there has been lengthy but unclear
speculation that the independently achieved performance benefits
of creatine supplementation might be negated by caffeine
supplementation (Trexler & Smith-Ryan, 2015).
Nitrate Nitrate enhances NO bioavailability via the NO3
−
–nitrite–NO
pathway, which plays an important role in the modulation of
skeletal muscle function (Jones, 2014). This pathway augments
exercise performance via an enhanced function of Type II muscle
fibers (Jones et al., 2016a), a reduced ATP cost of muscle force
production, an increased efficiency of mitochondrial respiration,
increased blood flow to the muscle, and a decrease in blood flow
to VO2 heterogeneities (Bailey et al., 2010).
• As for caffeine, responsiveness to nitrate supplementation is
individual, and protocols for repeated use within the same day need
planning. Furthermore, various research suggests a lack of response
for athletes with a well-developed aerobic capacity (i.e., VO2max
>60 ml/kg; Jones, 2014).
• Interactions with the concurrent use of other performance supplements
require consideration; at present, this has been investigated in relation
to use with caffeine with unclear results (Burke, 2017).
β-Alanine β-Alanine is a rate-limiting precursor to carnosine, an endogenous
intracellular (muscle) pH buffer during exercise (Lancha Junior
et al., 2015). Chronic, daily supplementation increases skeletal
muscle carnosine content (Saunders et al., 2017).
• Concurrent use of β-alanine and sodium bicarbonate
supplementation is logical when maximal buffering capacity is
needed; however, literature support for combined benefits is
premature.
Sodium
bicarbonate
Sodium bicarbonate acts as an extracellular (blood) buffer,
aiding intracellular pH regulation by raising the extracellular
pH and HCO3
−
concentrations (Katz et al., 1984; Lancha
Junior et al., 2015). The resultant pH gradient between the
intracellular and extracellular environments leads to efflux
of H+
and La−
from the exercising muscle (Katz et al., 1984;
Mainwood & Worsley-Brown, 1975).
• Potential for gut disturbances is high risk in running-based events,
likely due to the increased sodium content and large fluid intake
required to consume the supplement.
• Protocols for repeated use within the same day or successive days
need planning.
• Interactions with the concurrent use of other performance
supplements require consideration; concurrent use with caffeine
supplementation has been investigated in other sports and often
seen to counteract the benefits of the former due to gastrointestinal
side effects (Burke, 2017).
Note. PCr = phosphocreatine; CM = creatine monohydrate; NO = nitric oxide; ATP = adenosine triphosphate.
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acute and chronic performance gains, where power, strength, and
short-repeated bouts of high-intensity exercise are encountered.
Nitrate
Nitrate supplementation has been shown to promote improvements
in exercise tasks that predominately stress the aerobic energy
system, such as time to exhaustion (4–25% increased performance)
and sport-specific events (1–3% increased performance) lasting
<40 min (Jones, 2014; McMahon et al., 2017). In addition, nitrate
supplementation is proposed to enhance Type II muscle fiber
function (Bailey et al., 2015) resulting in the improvement (3–5%)
of high-intensity exercise efforts (Thompson et al., 2015; Wylie
et al., 2016). Current evidence is equivocal for such benefit to
exercise tasks lasting <12 min (Reynolds et al., 2016; Thompson
et al., 2016), although more work is needed in this area.
Nitrate-rich foods include leafy green and root vegetables
(i.e., spinach, rocket, celery, beetroot, etc.), although beetroot juice
is the more popular supplement choice for exercise settings
(McMahon et al., 2017). Acute performance benefits are generally
seen within 2–3 hr following a NO3
−
bolus of 5–9 mmol (310–
560 mg) (Hoon et al., 2014; Peeling et al., 2015); however, chronic
periods of NO3
−
intake (>3 days) also appear beneficial to performance
(Thompson et al., 2015, 2016).
There appears to be few side effects or limitations to nitrate
supplementation other than the potential for minor gastrointestinal
upset in some gut-sensitive athletes. In addition, an upper limit to
the benefits of NO3
−
consumption has been shown (i.e., no greater
benefit from 16.8 mmol [1,041 mg] vs. 8.4 mmol [521 mg]; Wylie
et al., 2013), and it might also be considered that performance
gains appear harder to obtain in elite athletes, with limited to no
benefits generally seen in athletes with a maximal oxygen uptake
(VO2max) > 60 ml/kg (Jones, 2014). Therefore, individual trials of
this supplement prior to use in competition are recommended to
ensure its use is effective.
β-Alanine
β-Alanine supplementation is associated with the improved tolerance
for maximal exercise in the range of 30 s to 10 min (Saunders
et al., 2017), with small but potentially meaningful performance
benefits (∼0.2–3%) shown during both continuous and intermittent
exercise tasks of this duration (Baguet et al., 2010; Chung et al.,
2012). β-Alanine supplementation increases the muscle content of
carnosine, an intracellular dipeptide with buffering, antioxidant,
and anti-inflammatory properties. Of these effects, enhanced buffering
is believed to explain the main performance benefit.
β-Alanine dosing strategies typically involve the consumption of
3.2–6.4 g/day, ingested via a split-dose regimen (i.e., 0.8–1.6 g every
3–4 hr) over an extended supplement time frame of 4–12 weeks
(Saunders et al., 2017). Regardless, a positive correlation between the
magnitude of muscle carnosine change and performance benefit
remains to be established (Saunders et al., 2017). Of note, the
effectiveness of this supplement has also been shown in well-trained
athletes (Bex et al., 2014; Saunders et al., 2017), although the
performance margins for improvement are evidently smaller
(Bellinger, 2014). A possible negative side effect of skin paresthesia
should be considered, although sustained release tablets are noted to
prevent this outcome and are reported to result in lower urinary loss of
the supplement, possibly resulting in improved whole-body β-alanine
retention (Decombaz et al., 2012). Finally, large interindividual
variations in muscle carnosine synthesis have been reported with
the use of β-alanine (Stautemas et al., 2018), and therefore, an
individualized approach to supplementation must be considered.
Sodium Bicarbonate
Sodium bicarbonate (NaHCO3) supplementation is proposed to
enhance the performance (∼2%) of short-term, high-intensity
sprints lasting ∼60 s in duration, with a reduced efficacy as the
effort duration exceeds 10 min (Carr et al., 2011a). In contrast to
β-alanine supplementation, which achieves a chronic elevation in
intracellular buffering capacity, NaHCO3 ingestion (consumed at a
dose of 0.2–0.4 g/kg BM) achieves an acute increase in extracellular/
blood buffering (Carr et al., 2011a) with peak blood bicarbonate
levels occurring after 75–180 min (when consuming 0.3 g/kg BM
NaHCO3), which appear to decrease by 3-hr postsupplementation
(Jones et al., 2016b). However, split doses (i.e., several smaller
doses) taken over a 30- to 60-min time period (Krustrup et al., 2015)
or serial loading with three to four smaller doses per day for two to
four consecutive days prior to an event (Burke, 2013) has been
proposed as methods to overcome the well-established gastrointestinal
distress associated with this supplement. Further strategies
used to minimize gastrointestinal distress include the coingestion
of NaHCO3 with a small carbohydrate-rich meal (∼1.5 g/kg BM
CHO; Carr et al., 2011b) or the use of the less effective but more
gut-friendly sodium citrate as an alternative (Requena et al., 2005).
In summary, despite the relatively robust evidence base to
support the consideration for use of these five supplements by welltrained
athlete populations, the potential side effects and negative
individual tolerance must be considered, and therefore, any supplement
use should be thoroughly trialed in training before competition.
Notwithstanding, as can be seen in Table 2, there are
potential challenges for the use of these supplements within
Table 3 Performance Supplements That May Achieve a Marginal Performance Gain in Track-and-Field Events
as Part of a Bespoke and Periodized Training and Nutrition Plan
Event Caffeine Creatine Nitrate β-Alanine Bicarbonate
Sprints: 100 m, 100-m hurdles, 110-m hurdles, and 200 m ✓ ✓
Sustained sprints: 400 m and 400-m hurdles ✓ ✓ ✓ ✓
Middle distance: 800 m, 1,500 m, 3,000 m, and steeple chase ✓ ✓ ✓ ✓
Long distance: 5,000 m, 10,000 m, cross-country, 20-km race walk, half
marathon, marathon, 50-km race walk, and mountain/ultra running
✓ ✓
Jumps and throws: high jump, long jump, triple jump, pole vault, discus throw,
hammer throw, javelin throw, and shot put
✓ ✓
Multievents: heptathlon and decathlon ✓ ✓ ✓ ✓ ✓
Readers are referred to Burke et al. (2019), da Costa et al. (2019), Slater et al. (2019); Stellingwerff et al. (2019), and Sygo et al. (2019).
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track-and-field events, including issues of repeated use and the
potential for interaction when several potentially useful supplements
are used together (Burke, 2017). The current literature relevant to
such use is not well understood and requires more research.
Therapeutic Nutritional Supplements
and Prophylactic Aids
In the context of this review, “therapeutic/prophylactic supplements”
are considered as nutritional aids that can be used either to
(a) correct a deficiency, (b) assist in the possible prevention of
illness and/or injury, or (c) help in the recovery from the stress of
physical workloads via an anti-inflammatory effect. For instance, it
is well known that iron deficiency can impair hematologic adaptation,
which left untreated can negatively impact on athletic performance
(Garvican et al., 2011). However, nutritional correction of
this issue via various intervention strategies has been regularly
shown to have a positive impact on correcting the underlying
deficiency and enhancing athlete performance (Dawson et al.,
2006; Garvican et al., 2011; Woods et al., 2014).
Regarding illness, there is strong evidence to suggest that
immunodepression can occur as a result of strenuous exercise
(Castell et al., 2019; Peake et al., 2017), and a high incidence
of upper respiratory tract illness is frequently reported (Drew et al.,
2018; Nieman, 1994), before and particularly after endurance
events. Low-energy availability has been identified as a key
nutritional factor in such illness (Drew et al., 2018; Heikura
et al., 2018); however, the provision of nutritional supplements
to alleviate exercise-induced immunodepression and to aid more
rapid recovery in athletes has also been well studied. Sometimes
certain supplements initially appear promising, but further intensive
investigation fails to provide sufficient evidence of consistent
beneficial effects on some aspects of exercise-induced immunodepression.
As different nutritional supplements become unfashionable,
whether targeting immunodepression or performance,
others take their place; however, the pros and cons of these
need to be carefully studied. For instance, probiotic supplementation
has been investigated in recent years (as have prebiotics), with
preliminary evidence of positive effects on immune function (Cox
et al., 2010) that might support the consistency of training and
competition. However, the effects of such supplementation are
dependent on appropriate doses of live bacteria of specific strains
(e.g., Lactobacillus, Bifidobacterium), and larger studies are still
needed to provide definitive evidence that probiotics benefit the
immune function of athletes. Glutamine and branched chain amino
acids, which are often marketed to support bodybuilding and
postexercise recovery, also have an unclear role in supporting
immune function in athletes (Bermon et al., 2017). Clearly, immunonutrition
is an emerging and important area for consideration
in the use of dietary supplements for athlete populations, and as
such, the reader is directed to recent reviews in this area (Bermon
et al., 2017; Castell et al., 2019), in addition to the comprehensive
paper on feeding the immune system (Calder, 2013).
With respect to the inflammatory response, there is a growing
body of work that is investigating anti-inflammatory and antioxidant
aspects of various foods and supplements. For instance, food
polyphenols possess strong antioxidant and anti-inflammatory
properties (Tsao, 2010) that may be beneficial to exercise recovery.
Specifically, the high-anthocyanin content of tart Montmorency
cherries is proposed to reduce the inflammatory and oxidative
stress responses to strenuous exercise, such as a marathon
(Dimitriou et al., 2015; Howatson et al., 2010), or consecutive
days of intermittent high-intensity activity (Bell et al., 2014). This
may be particularly relevant to the heavy training loads of many
high-performance athletes, as well as the competition recovery in
multievents in track-and-field athletics or the programs of middledistance
runners with heats and finals across several events at major
competition. Other anti-inflammatory nutrients include flavonoids
such as quercetin and green tea extract, plus fish oil, each of which
may have a beneficial effect on delayed onset muscle soreness
(Ranchordas et al., 2018). Consumption of highly colored vegetables/fruit
is often advised; this advice is appropriate for elite
athletes (previously mentioned), as these flavonoids (including
blueberries, blackcurrants, and cherries) have a beneficial effect
on exercise-induced inflammation, muscle damage, and illness
(Bermon et al., 2017). In addition, it is proposed that some of
these foods may also have the ability to reduce exercise-induced
oxidative stress; however, there is currently some controversy
about whether high-dose antioxidant supplementation (in the
form of pills, powders, and tablets) is advisable to alleviate
exercise-induced generation of reactive oxygen/nitrogen species.
Emerging evidence suggests that antioxidant supplementation
mitigates important exercise-induced adaptations, which may
also extend to the immune system (Bermon et al., 2017).
In summary, there are various roles for nutritional supplements
for what may be considered “therapeutic applications”; however,
much more work is needed in this area to assess the efficacy of
these supplements and to determine their true effect on athletic
performance.
Disadvantages of Sports Foods
and Dietary Supplements
The decision to take a supplement will always involve an attempt to
gain a functional advantage, in most cases being health protection/
improvement, physique management or enhanced recovery, or a
direct performance enhancement. Contrary to these potential benefits,
is the consideration that the supplement inherently possesses certain
risks against its use; such risks can be divided into three categories.
Risks of Labeled Content
All supplements worldwide are legally bound to be sold in
packages that contain a listing of the ingredients. Some national
legislations may be stricter than others in setting and enforcing
the list of permitted ingredients in supplements, but any consumer,
and certainly, athletes who consider taking supplements to support
their athletic performance should not consume a product with
ingredients that cannot be recognized in a basic Internet search.
A so-called “proprietary-blend” listing exotic names and claiming
commercial Intellectual property cannot be considered a transparent
listing of ingredients.
Even when supplement contents are clearly listed, they cannot
necessarily all be considered safe. In many countries, the regulations
covering supplements do not require specific testing before going to
market but rely on notification of adverse events to remove unsafe
products from sale. This has led to the inclusion of toxic substances
in highly popular products, for example, the bodybuilding and
weight loss supplement OxyELITE Pro (USPlabs, Hermosa
Beach, CA) was found to be associated with at least one death and
a cluster of serious liver complications, attributed to the ingredient
1,3-dimethylhexanamine (also known as DMAA; Johnston et al.,
2016). This was subsequently removed from the list of ingredients
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204 Peeling et al.
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that may be included in supplements across many countries. Even
where some ingredients might have been considered to be “safe
use,” basic toxicology laws dictate that any substance has the
potential to lead to health-deteriorating effects when used by
some individuals in specific scenarios or doses. For athletes, this
is often preceded by decreased performance.
Risks of Undeclared or Unlabeled Content
Despite existing legislations, some supplements have been found to
contain contaminants or health hazards, such as molds, glass, or
animal feces (Benedict et al., 2016; Katz, 2013). A specific risk for
competitive athletes is the undeclared presence of substances that
are banned under the World Anti-Doping Agency (WADA) antidoping
code. Of course, these substances are sometimes identified
on product labels, but athletes are either unaware that they are
banned or are confused by technical/chemical names. For example,
DMAA is a banned substance and has been included in supplements
under a variety of other names including geranium oil/
extract or geranamine; this no doubt contributed to many publicized
and less well-known cases of anti-doping rule violations.
This risk of inadvertent doping from supplement use has been
known for at least 30 years but is still very much present (de Hon &
Coumans, 2007; Geyer et al., 2004; Martinez-Sanz et al., 2017).
Indeed, the list of prohibited substances that have been detected in
supplements includes stimulants, anabolic agents, selective androgen
receptor modulators, diuretics, anorectics, and β2 agonists
(Martinez-Sanz et al., 2017). When the amounts of banned substances
in supplements are large enough to generate a direct effect
(e.g., stimulant symptoms), this is an obvious sign of potential
contamination to a consumer and sometimes an indicator of intentional
but undeclared manufacturing practices (Geyer et al., 2008;
Parr et al., 2007, 2008). But the risks of unintentional contamination
from adulterated raw ingredients or cross-contamination of machinery,
even by the most careful manufacturers, should not be underestimated
and will never be zero (Judkins et al., 2010; Maughan
et al., 2018b). Because of the ever-improving analytical capabilities
in antidoping laboratories, trace amounts of prohibited substances
can be found in biological samples taken at doping control. As a
result, it cannot be stressed enough that athletes need to be aware
that the WADA rules of strict liability mean that the detection of a
prohibited substance in an athlete’s specimen will be treated as
an anti-doping rule violations, irrespective of the intentions behind
it (Abbott, 2004; Hughes, 2015). Furthermore, it should also be
understood that coaches, support personnel, parents, friends, and
anyone else involved in the life of an athlete can also be implicated
in an anti-doping rule violations, with WADA imposed sanctions
(i.e., suspensions from sport) applicable. Using only products that
have been audited by a third-party testing program and found to be
free of banned substances will help to lower, but not completely
eliminate, this risk. However, the general avoidance of the high-risk
multi-ingredient supplements promoted as preworkouts or weight
loss and bodybuilding products is recommended.
Noncontent-Related Risks
Some final concerns or issues regarding use of supplements and
sports foods need to be considered. First, athletes should realize
that any benefit of legal supplementation is bound to be small.
Expecting too much of an intervention that addresses only the top
end of one aspect of athletic performance may lead to disappointments
and distract from other, more powerful, aspects of elite
athletic training. Second, expense must also be considered,
especially when finite resources could have been used in other
areas of the preparation of an elite athlete’s life. Finally, concerns
have been raised that supplement use may be a stepping stone to
taking other substances, including those prohibited by antidoping
regulations (Backhouse et al., 2013). With this in mind, attention
should be directed toward the ethical challenges of athlete product
marketing and the influence of such approaches on encouraging
undue supplement use, especially on young/developing athletes.
In summary, the very real risks of taking supplements should be
carefully considered by competitive athletes. Of note, Castell et al.
(2015) published an A–Z Guide on 140 nutritional supplements in
exercise and health; this includes efficacy tables ranging from those
supplements shown to be ergogenically effective to those banned by
WADA as being harmful or illegal. Readers might find it useful to
consult this book prior to embarking on a course of supplements.
Conclusion: A Pragmatic Approach to
Making Decisions about Supplements
In the past, athletes and coaches often worked in a parallel universe
to their expert groups (e.g., governing bodies of sport) and service
teams (e.g., sports scientists, dietitian, and physicians) with regard
to performance supplements, with the former favoring supplement
use based on their interest in performance gains and the latter being
risk averse and dismissive of such products. The modern landscape,
at least for high-performance athletes, has seen a unification of
effort and intent, with many parties now working together to take a
pragmatic approach to managing a risk:benefit audit around the use
of sports foods, therapeutic/prophylactic supplements, and performance
supplements. This has been led by organizations such as
the International Olympic Committee and the Australian Institute
of Sport, that have produced expert statements (Maughan et al.,
2018a) and education resources (Burke & Cato, 2015) to guide a
proactive but evidence-based consideration of the use of these
products. In the case of sports foods, track-and-field athletes are
guided to seek the expertise of an appropriately qualified sports
nutrition professional who can help them balance the expense of
using these specialized products with the scenarios in which
they offer genuine performance benefits. Therapeutic/prophylactic
supplements should involve the expertise of a sports physician,
especially when a diagnosis of medical issues and nutrient deficiencies
is needed. A decision-tree approach to the use of performance
supplements (Figure 1), especially in collaboration with
sports science/nutrition experts, will help to ensure that any
products that are used are appropriate to the athlete’s age and
maturation in their event, integrated into the athlete’s plan according
to evidence-based protocols and appropriate scenarios, and
chosen on the basis of being at low risk of contamination with
banned or harmful ingredients. Ultimately, it is pertinent that sports
foods and nutritional supplements should only be considered where
a strong evidence base supports their use as safe, legal and effective
and that such supplements are trialed thoroughly by the individual
before committing to use in a competition setting.
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