Sports Foods and Dietary Supplements for Optimal Function and Performance Enhancement in Track-and-Field Athletes

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 conclu de that it is pertinent for sports foods and nutritional supplemen ts 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, particu-

larly within elite sport where marginal performance gains are pursued.

The following review presents general considerations for track-and-

ﬁeld 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 perfor-

mance 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 Austra-

lian Institute of Sport, M t Claremont, W estern Aust ralia, Austr alia. Castel l 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 corresp ondence to Peter

Peeling at [email protected].

198

International Journal of Sport Nutrition and Exercise Metabolism, 2019, 29, 198-209

https://doi.org/10.1123/ijsnem.2018-0271

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, physiol-

ogists, sports physicians) working with athlete cohorts should

be aware of differences in the incidence and t ype of supplement

use within a given group of athletes, with caliber and sex being

discriminating characteristics. For further i nsights into the prev-

alence 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/b etween competi-

tion 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 hydra-

tion 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 supple-

ments 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 “everyd ay-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 th ose 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 sup-

ported 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 supple-

ment use by high-performance athletes (Maughan et al., 2018a)

proposes that only ﬁve performance suppleme nts 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 track-

and-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), consu med ∼60 min prior to exercise in the form of anhy-

drous 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 respon ses 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). Interestingl y, 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 withd rawal

(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) con-

sumed 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 high-

performance track-and-ﬁeld athletes in the longer sprints, middle

distance, and endurance/ultraendurance events to consider compe-

tition 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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200 Peeling et al.

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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 sec-

ondary 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 high-

intensity 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 NO

−

–nitrite–NO

pathway, which plays an importantroleinthemodulationof

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 VO

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., VO

max

>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 HCO

−

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 performan ce)

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 beneﬁtto

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, et c.), 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 NO

−

bolus of 5–9 mmol (310–

560 mg) (Hoon et al., 2014; Peeling et al., 2015); however, chronic

periods of NO

−

intake (>3 days) also appear beneﬁcial to perfor-

mance (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 NO

−

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

(VO

max) > 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 toler-

ance 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 buff-

ering 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 (NaHCO

) 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, NaHCO

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

NaHCO

), 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 method s to overcome the well-established gastroin-

testinal distress associated with this supplement. Further strategies

used to minimize gastrointestinal distress include the coingestion

of NaHCO

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 supplemen ts by well-

trained athlete populations, the potential side effects and negative

individual tolerance must be considered, and therefore, any sup-

plement use should be thoroughly trialed in training before com-

petition. 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 supple-

ments” 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 adapta-

tion, which left untreated can negatively impact on athletic perfor-

mance ( 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 inten-

sive investigation fails to provide sufﬁcient evidence of consistent

beneﬁcial effects on some aspects of exercise-induced immuno-

depression. As different nutritional supplements become unfash-

ionable, whether targeting immunodepression or performance,

others take their place; however, the pros and cons of these

need to be carefully studied. For instance, probiotic supplementa-

tion 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, im-

munonutrition 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 antioxi-

dant 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 recove ry.

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 middle-

distance 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 vege-

tables/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 inﬂammati on, 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 transpar-

ent 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) anti-

doping 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 supple-

ments under a variety of other names including geranium oil/

extract or geranamine; this no doubt contributed to many publi-

cized 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 andro-

gen receptor modulators, diuretics , anorectics, and β2 agonists

(Martinez-Sanz et al., 2017). When the amounts of banned sub-

stances 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 inten-

tional 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 machin-

ery, even by the most careful manufacturers, should not be under-

estimated 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 disappoint-

ments 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 perfor-

mance 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 deﬁ-

ciencies is needed. A decision-tree approach to the use of perfor-

mance supplements (Figure 1), especia lly 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 accord-

ing 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 wh ere

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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