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Given that this is a narrative review, the standard subsections that are presented in a systematic review or original article
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e.g. Tufford, A.R., Calder, P.C., Van’t Veer, P. et al. Is nutrition science ready for the twenty-first century? Moving towards
transdisciplinary impacts in a changing world. Eur J Nutr 59, 1–10 (2020). https://doi.org/10.1007/s00394-020-02241-0
3.Please provide the volume number for reference [16].
EJM Fares B Kayser (2011) Carbohydrate mouth rinse effects on exercise capacity in pre- and postprandial states. J
Nutr Metab 2011: 385962.
4.Kindly check and confirm the details for reference [135] are correctly identified.
Please amend to Gaskell SK, Snipe RMJ, Costa RJS (2019) Test re-test reliability of a modified visual analogue scale
assessment tool for determining incidence and severity of gastrointestinal symptoms in response to exercise stress. Int J Sports
Nutr Exerc Metab 29:411–419
5.Please provide the volume number for reference [136, 137].
Newcomb RD, Xia MB, Reed DR (2012) Heritable differences in chemosensory ability among humans. Flavour 1:9,
https://doi.org/10.1186/2044-7248-1-9
Pickering C, Kiely J (2018) What should we do about habitual caffeine use in athletes? Sports Med 49(6):833-842. doi:
10.1007/s40279-018-0980-7.
6.As References [24] and [107] are same, we have deleted the duplicate reference and renumbered
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7.AUTHOR: As References [24] and [107] are same, we have deleted the duplicate reference and
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Review
Can taste be ergogenic?
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Russ Best,
Email Russell.Best@wintec.ac.nz
Kerin McDonald,
Philip Hurst,
Craig Pickering,
Centre for Sports Science and Human
Performance, Wintec, Hamilton, 3288 New Zealand
School of Health and Social Care, Teesside University, Middlesbrough, TS1
3BX UK
School of Human and Life Sciences, Canterbury Christ Church
University, Canterbury, UK
Institute of Coaching and Performance, School of Sport and
Wellbeing, University of Central Lancashire, Preston, PR1 2HE UK
Received: 7 October 2019 / Accepted: 6 May 2020
Abstract
Taste is a homeostatic function that conveys valuable information, such as
energy density, readiness to eat, or toxicity of foodstuffs. Taste is not limited
to the oral cavity but affects multiple physiological systems. In this review, we
outline the ergogenic potential of substances that impart bitter, sweet, hot and
cold tastes administered prior to and during exercise performance and whether
the ergogenic benefits of taste are attributable to the placebo effect.
Carbohydrate mouth rinsing seemingly improves endurance performance,
along with a potentially ergogenic effect of oral exposure to both bitter tastants
and caffeine although subsequent ingestion of bitter mouth rinses is likely
required to enhance performance. Hot and cold tastes may prove beneficial in
circumstances where athletes’ thermal state may be challenged. Efficacy is not
limited to taste, but extends to the stimulation of targeted receptors in the oral
cavity and throughout the digestive tract, relaying signals pertaining to energy
availability and temperature to appropriate neural centres. Dose, frequency and
timing of tastant application likely require personalisation to be most effective,
and can be enhanced or confounded by factors that relate to the placebo effect,
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highlighting taste as a critical factor in designing and administering applied
sports science interventions.
AQ1
AQ2
Keywords
Taste
Carbohydrate
Caffeine
Menthol
Capsaicin
Bitter
Introduction
Taste is a homeostatic function that aids in deciding what to eat, and acts as a
precursor for digestion [1]. Human taste and preferences are evolved due to
nutrient availabilities within our ancestral environments [2], where they
conveyed information, such as energy density, readiness to eat, or toxicity [1, 3].
Despite being the area most densely populated with taste receptors, taste is not
strictly confined to the oral cavity, but frequently incorporates other sensory
inputs from the upper digestive tract and auditory, olfactory and visual systems
[1, 4, 5, 6, 7, 8, 9]. This is most evident in those who suffer with ageusia (loss of
taste), or anosmia (loss of smell), and still respond physiologically to tastes [3,
10], demonstrating taste as a chemical interaction between a chemesthetic agent
and receptors, which drives either ingestion or aversion and accompanying
hedonic sensations.
Assessment of the physiological responses to taste has not escaped sports
scientists, with many ‘tastes’ now investigated within the literature [11, 12, 13,
14, 15] with a view to attenuating fatigue or improving physical or cognitive
performance. Depending upon the tastant investigated, impressions of energy
availability [16, 17], thermal perceptions [11, 12, 18] and central drive [15, 19]
may be altered. Secondary outcomes may also include modifications in
autonomic function [20, 21, 22], thirst [23, 24] and ventilation [25, 26, 27], with
further downstream effects depending upon whether tastants are ingested or
simply rinsed around the oral cavity and expectorated.
These outcomes are likely to be useful to athletes, but depend heavily upon their
exercise modality, prior exposure to and preference for specific tastants, as well
as the availability of tastants during an exercise bout. Placebo effects associated
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with tastants cannot be excluded and indeed may be maximised by including a
carefully chosen taste component in personalised sports nutrition interventions or
matching tastes of interventions to other sensory expectations, such as colour
[28, 29]. Previous work has asked whether “the [central] governor has a sweet
tooth” [14]; in this review, we explore the ergogenic potential of different tastes
administered prior to and during exercise performance. We also raise the
question of whether the ergogenic benefits of taste are attributable to the placebo
effect. Recommendations for athletes, practitioners, and future research
directions are also provided throughout.
Sweet and bitter tastants and athletic performance
Carbohydrate
The efficacy of carbohydrates as a means of supporting endurance performance
is well established [30]. However, a clear, over-riding mechanism by which
carbohydrate enhances performance is currently unknown; during exercise, only
about a quarter of ingested carbohydrate enters peripheral circulation [31], with
exogenous carbohydrate demonstrated to contribute only a small proportion of
the carbohydrate oxidised during the late stages of prolonged exercise [32]. This
lack of a clear metabolic mechanism leads to speculation that the consumption of
carbohydrates during exercise may stimulate central pathways associated with
sensations of reward or energy availability, which in turn has a performance-
enhancing effect [33]. To test this hypothesis, researchers allowed subjects to
rinse a carbohydrate solution around the mouth, but not ingest it, removing the
metabolic effects of carbohydrate on performance. In the last decade, an
exponential increase in research on this topic has been carried out, with a number
of reviews [14, 33, 34, 36, 36] demonstrating a clear ergogenic effect of a
carbohydrate mouth rinse on endurance performance, particularly in glycogen-
depleted participants.
Given that little carbohydrate is absorbed in the oral activity during mouth
rinsing, the mechanism(s) by which carbohydrate mouth rinses enhance
performance are likely to be central in nature [14]. The tongue contains a number
of taste receptors capable of detecting sweet stimuli [37] and these taste
receptors when stimulated activate dopaminergic pathways and reward centres
within the brain [17, 38]. In turn, this increase in reward may enhance motivation
to exercise, allowing the athlete to self-select higher exercise intensities, and
reducing the impact of peripheral fatigue-associated signals under both the
central governor [39] and psychobiological [40] models of fatigue. There may
also be a feedforward effect, whereby the activation of oral carbohydrate
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receptors suggests that energy is being consumed, allowing for an increase in
exercise intensity, although this hypothesis has yet to be experimentally tested.
At present, it appears that the ergogenic effects of a carbohydrate mouth rinse are
not taste related per se. This is demonstrated by the fact that tasteless
carbohydrates, such as maltodextrin, are ergogenic in a mouth-rinse solution
[36], and also activate brain regions similarly to sweet-tasting carbohydrates,
such as sucrose [17]. Similarly, artificial sweeteners provide a sweet taste, but a
far smaller activation of key brain regions compared to sucrose [41].
Accordingly, it seems likely that it is the carbohydrate binding to as-of-yet
unidentified oral carbohydrate receptors, as opposed to taste itself, that drives the
ergogenic effects of a carbohydrate mouth rinse [14].
Bitter tastants
Building on the potential ergogenic effects of a sweet taste as mediated by
carbohydrate rinsing (detailed in Sect. 2.1), Gam and colleagues explored the use
of bitter tastants on exercise performance (reviewed in Gam et al. [19]). The
potential relationship between bitter taste and enhanced exercise performance has
a strong molecular underpinning, given that bitter tastants activate similar areas
of the brain as sweet tastes [42], with these brain areas being implicated in
aspects, such as motor control and the processing of emotions [19].
In their first study exploring the ergogenic effects of a bitter tastant, Gam and
colleagues [43] administered 14 competitive male cyclists with a bitter solution
containing 2 mM quinine, which was rinsed in the mouth for 10 s and then
ingested. The quinine solution enhanced mean power output in a 30-s maximum
cycle by 2.4% compared to an aspartame (sweet taste) mouth and by 3.9%
compared to water. In a subsequent study [44], a stronger concentration (10 mM)
of quinine was utilised, but the solution was only rinsed around the mouth and
not ingested. In this scenario, there was no ergogenic effect of the bitter solution
on a 30-s cycle sprint, suggesting that the ingestion of the bitter solution is
potentially important. The proposed mechanism underpinning the need for
ingestion is that there are an increased number of bitter taste receptors beyond
the oral cavity in the upper gastrointestinal tract [45] which are not activated
following mouth rinse only. Outside the work of Gam and colleagues [43, 44,
46], there is little additional research exploring the ergogenic effects of a bitter
tastant, and so further research in this area is warranted. This would be
particularly pertinent from a practical approach, with strong bitter tastants—such
as those used in the research by Gam and colleagues—able to induce nausea in
some subjects upon ingestion [43]; given this information, further research
exploring the optimal intensity of the bitter taste would likely be very useful.
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Caffeine
Given the demonstrated ergogenic effects of an ingested bitter tastant [43, 46],
Pickering [15] recently reviewed whether caffeine—itself a bitter tastant [47]
that has been shown to activate bitter taste receptors located in the oral cavity
[48]—exerted some of its well-established ergogenic effects [49] via its bitter
taste. A small number of studies [50, 51, 52, 53, 54, 55, 56] have utilised a
caffeine-mouth rinsing protocol as a method to enhance performance. Studies
that demonstrated an ergogenic effect employed a repeated 6-s Wingate sprint
protocol [50, 53] or a self-paced endurance effort over 30 min [56]; whereas
investigations that showed no effect employed either fixed work rate [51],
progressive running [55] or repetitions to failure [52] models. Whilst the results
are currently equivocal, there is a trend for no-demonstrated performance
enhancement when caffeine is rinsed around the mouth for both endurance and
high-intensity exercise [15]. The reasons for this are currently unclear; it may be
that caffeine’s bitter taste is not ergogenic that the caffeine solutions utilised
were not sufficiently bitter to evoke an ergogenic effect or that of like quinine
[44], ingestion of caffeine is required for its bitter taste to be ergogenic [54].
However, caffeine mouth rinses have been demonstrated to improve cognitive
function during exercise [57] and limit mental fatigue [58], suggesting that there
might be psychological ergogenic effect of caffeine mouth rinses—and,
therefore, potentially caffeine’s bitter taste—for future research to uncover.
Sweet and bitter tastes section summary
Based on the research discussed here, there is a clear ergogenic effect of
carbohydrate mouth rinsing on endurance performance [14], along with a
potentially ergogenic effect of oral exposure to both bitter tastants [19] and
caffeine [15] although in the latter two cases, subsequent ingestion of the mouth
rinse is likely required to enhance performance. Regarding bitter tastants, it is
believed that this subsequent ingestion is required to further stimulate bitter taste
receptors in the upper gastrointestinal tract [44]. These bitter taste receptors are
not necessarily linked to gustatory neurons [59], meaning that this activation is
not associated with “tasting” the bitterness. Additionally, tasteless carbohydrates
evoke an identical ergogenic effect as sweet carbohydrates in a mouth rinse [36],
whilst sweet-tasting artificial sweeteners do not [33]. As such, it is important to
note that the sensation of a particular taste may not be driving these ergogenic
effects, but instead it is likely the stimulation of other receptors, which in turn
act centrally to enhance performance [14].
Thermal tastants and athletic performance
Chilli and capsaicin
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For millennia, humans have included spices, such as chili peppers in their diets,
experiencing and often enduring the associated pungent sensation of oral heat
[60, 61]. Mechanistically, the sensation of increased temperature derives from the
interaction between the compound capsaicin (8-methyl-N-vanillyl-6-
nonenamide) and transient receptor potential vanilloid-1 proteins (TRPV1) [62].
TRPV1 is also stimulated when temperatures are elevated [63]; hence, foods
containing capsaicin are perceived as being hot [62]. This perceptual heat is not
limited to taste, with capsaicin also used in topical ointments, patches and sprays
as a temporary but targeted analgesic [61]. The application of which is widely
used by recreational and elite athletes to reduce joint and muscle pain, whereas
the possible ergogenic properties of capsaicin taste and ingestion are an emerging
field.
To date, only four studies have investigated the ergogenic properties of capsaicin
ingestion [64, 65, 66] or mouth swilling [12] in humans, and as such an array of
protocols, dosages and performance measures have been assessed. Three studies
have investigated the effect of acute supplementation of capsaicin (12 mg)
45 min prior to athletic performance in a 1500-m running time trial [65], four
sets of 70% 1RM repeated squats to failure [13], and time to exhaustion during
repeated 15-s treadmill running at 120% VO with 15-s rest intervals [66].
Capsaicin supplementation improved 1500-m time-trial performance (CAP
371.6 ± 40.8 s vs. Pla 376.7 ± 39 s), total mass lifted (CAP 3,919.4 ± 1,227.4 kg
vs. Pla 3,179.6 ± 942.4 kg) and time to exhaustion (CAP 1530 ± 515 s vs. Pla
1342 ± 446 s) compared to placebo. RPE was also significantly lower, although
no differences in blood lactate were shown [13, 65]. Researchers suggested that
capsaicin supplementation may have stimulated activation of TRPV1 in skeletal
muscle increasing calcium release at the sarcoplasmic reticulum, a phenomenon
seen in rodent studies [67]. This increased influx of calcium may have resulted in
greater actin and myosin interactions leading to improved performance.
Alternatively, capsaicin has been shown to have an analgesic effect [61], which
may have lowered RPE values and facilitated performance [13]. Increased
endurance capabilities may also be facilitated by spared glycogen and
concomitant increase in lipolysis through capsaicin ingestion [68, 69, 70].
The above literature suggests that ingesting capsaicin as a capsule is effective for
improving sport performance. However, when capsaicin is ingested as food, the
ergogenic effects are not consistent. A 7-day ingestion of cayenne herbal
supplement totalling 25.8 mg day of capsaicin did not result in improved 30-m
sprint times nor a reduction in RPE or muscle soreness scores [64]. Whereas,
Lim et al. [71], showed the ingestion of 10 g of hot red peppers 2.5 h prior to
exercise (150 w cycling for 60 min) significantly elevated both respiratory
2Peak
−1
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quotient and blood lactate levels at rest and during exercise, suggesting increased
carbohydrate oxidation. The differences in supplementation type (cayenne vs. red
peppers), dose amount (25.8 vs. 12 mg) and protocol (repeated vs. acute) likely
contributed to the variation in efficacy; the higher dose in particular may
negatively influence GI motility [13]. This is supported by a rodent study that
found swimming endurance was optimal when mice were supplemented with
10 mg/kg, 2 h prior to performance [72]. This dose and ingestion timing appear
to be a ‘sweet spot’, with doses or timings that fall below or exceed these values
proving ineffective or deleterious to performance, respectively [73]. It should be
noted that a similar dosage in a human diet would equate to 100 g of red chilli
pepper consumption [74], which would be impractical and likely cause serious
gastrointestinal (GI) discomfort [69].
As TRPV1 receptors are found in the oesophagus, stomach, intestine and colon
[75], the possibility of GI discomfort is increased following capsaicin
consumption. In a study where participants ingested capsaicin capsules, moderate
visceral pain was reported following a median dose of 1 mg [76]. Opheim and
Rankin’s [64] repeated sprint study reported GI distress symptoms increased 6.3
times compared to placebo and resulted in three participants withdrawing from
the study [64]; thus, capsaicin-induced GI discomfort may deleteriously affect
performance. A possible solution may be the use of a unique variety of chili
peppers, CH-19 Sweet, which contain capsiate, a non-pungent capsaicin
analogue that has been shown to activate TRPV1 [69, 77] and return similar
responses as capsaicin, including improving time to exhaustion in rodent studies
[69, 74]. Haramizu et al. [69] also observed no aversion to capsiate ingestion;
like carbohydrate, efficacy of capsaicin supplementation may be less about the
taste of the intervention and more about the activation of desired receptors.
In each of the aforementioned human studies [64, 65, 66], capsaicin was
delivered via a capsule. As a result, receptors in the oral cavity were by-passed,
eliminating capsaicin’s pungent oral sensation. Recently, Gibson et al. [12],
employed a 0.2% capsaicin mouth swill every 10 min during repeated 6-s cycle
ergometer sprints in the heat (40 °C, 40% relative humidity). This delivery
method (mouth swill) directly targets TRPV1 channels in the mouth and reduces
possible GI discomfort; yet, results showed no difference in peak power, work
performed or RPE across experimental groups (control, placebo, menthol and
capsaicin mouth swills). Interestingly, thermal perception (comfort and
sensation) was not altered after capsaicin mouth swill compared to control and
placebo, but menthol trials reported significant improvements in thermal comfort
[12].
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Despite many reported health benefits from the regular consumption of capsaicin
(e.g. improved cardiovascular function, diabetes control, etc. [61]), the effect of
capsaicin on sports performance is limited. It would appear that acute
supplementation (45 min prior to exercise) of low-dose capsaicin (12 mg) may
induce an ergogenic response in near maximal exercise [65, 66]. Further
investigation on precise timing, dosage and delivery methods are required.
Minimising GI discomfort should be a primary consideration for researchers
while still effectively stimulating TRPV1 channels.
Menthol
Menthol imparts its familiar minty flavour via stimulation of transient receptor
melastatin 8 (TRP-M8) receptors. These sodium voltage-gated ion channels are
especially concentrated in the trigeminal nerve, which innervates the oral cavity,
and when stimulated mimics a ‘cold’ temperature range (8–28 ºC; [78]), feeling
and tasting ‘cool’. The effects of menthol are inversely proportional to the
thickness of the stratum corneum [11, 79]; hence, application to the oral cavity
often confers a greater stimulatory effect than topical menthol application [11,
80]. Menthol can be experienced by anosmic individuals [81], emphasising its
neurological mechanism [82, 83], but the ability to detect menthol has been
shown to decline with age [84], suggesting higher menthol concentrations may
be required to elicit ergogenic effects in masters athletes.
Menthol application to the oral cavity can be individualised using a preferred
menthol concentration and may be enhanced using colour [29]. A relative dose is
yet to be administered to athletes, but an experimental dose of 30 mg/kg was
prescribed by food scientists investigating the effects of carbonation and menthol
upon oral cooling [85]. Partnering menthol’s chemosensory cooling effects with
physiological coolants, such as ice slurries may further enhance its efficacy [86,
87, 88], but there is an increased risk of overstimulation of the trigeminal system
potentially resulting in “brain freeze” [89, 90, 91].
Performance literature, to date, has assessed the effects of menthol mouth
swilling upon cycling in intermittent [12] and time to exhaustion [25, 26, 92]
models, as well as running time-trial performance [27, 93]. Intermittent
performance was not improved; however, time to exhaustion and time-trial
performance demonstrate trivial-moderate improvements (Hedge’s g: 0.40; 0.04
– 0.76 [18]). Concomitant improvements in thermal comfort and thermal
sensation are noted following menthol exposure [12, 25, 27, 92, 93], with an
increase in ventilation also reported [25, 26, 27]. These effects are likely
mediated by TRP-M8 expression and stimulation of jugular and nodose neurons
which provide interoceptive feedback from the alimentary organs and the
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cardiorespiratory system [94, 95]. This may explain the increase in ventilation
seen with menthol mouth swilling. The rate and volume of airflow passing
through the nasal canal also increase TRP-M8 activity and ventilation [96, 97,
98]. Whilst this can be contrived in the laboratory, it is likely that this effect is
more apparent in ecologically valid settings with faster wind and performance
velocities.
Despite participants reporting feeling cooler, no changes in body temperature
have been reported to date following the oral application of menthol exclusively
[12, 25, 26, 27, 92, 93]. An emerging secondary effect of menthol use is an
attenuation of thirst [23]; however, the potential ergogenic and contextual
relevance of this are unknown as of yet, highlighting that menthol should be
applied to sport cautiously. Thirst, more so than taste, conveys a homeostatic
message regarding hydration status [99, 100]; however, thirst can also be
quenched by carbonated and cool/cold products [85, 100, 101, 102, 103],
emphasising the role of TRP-M8 receptors in our somatosensory interpretation of
cool and refreshing [24, 104, 105, 106] and the potential for deception-driven
dehydration if water intake is attenuated in an event where hydration status is
performance limiting e.g. ultramarathon [107, 108], or in athletes with
abnormally high sweat rates [109].
Thermal tastants section summary
Whilst the research pertaining to the TRP channel afferents capsaicin and
menthol is in its infancy, in comparison to caffeine and carbohydrate, these
thermal tastes may prove ergogenic under certain circumstances and likely serve
to disrupt an athlete’s perception of their thermal state, which may be ergogenic
of itself. Individual sensory thresholds for effective doses likely exist, and timing
of administration requires further elucidation, with the potential impact of these
strategies on GI discomfort an important consideration. What is clear though is
that if capsaicin and menthol are to be supplemented, attaining meaningful doses
via wholefoods would either be impractical or ineffective [73, 110]
The sweet taste of placebo
The ergogenic effect of taste could be influenced by the placebo effect. The
placebo effect is a desirable outcome resulting from a person’s expected and/or
learned response to a treatment or situation [28]. Placebo effects have shown to
improve sport performance [111, 112, 113], with a systematic review reporting
small to moderate effects for nutritional (d = 0.35) and mechanical (d = 0.47)
ergogenic aids [114]. Placebo effects are often created within a psychosocial
context that influences a person’s response to a placebo. These include the
interaction between the person receiving the placebo and the person
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administering it (e.g. participant and researcher), the environment in which it is
delivered (e.g. laboratory) and sensory processes, such as colour, smell and taste
[28]. The placebo effect is, therefore, a response to a signal, or set of signals,
which conveys information that trigger self-regulatory mechanisms.
While there are many theories to propose the underpinning mechanisms of the
placebo effect (e.g. expectancy theory, classical conditioning), in this paper, we
adopt a broader and general conception that the placebo effect of taste could be
explained through an anticipation on resource allocation. Beedie et al. [115],
recently argued that the brain modulates and anticipates the relationship between
a signal (e.g. taste) and the body, which regulates subsequent resource allocation.
Based on this understanding, the taste of glucose, for example, signals to the
brain that resources will soon be available, which in turn, regulates the resources
allocated. Theoretically, if a placebo tastes like glucose, the brain would
anticipate that glucose has been received and subsequently offloads more
resources. In short, the placebo effect may impact the ergogenic effect of taste,
through its application of signalling to the brain that more resources are
available, which sets in motion a chain of self-regulatory responses that produce
an improvement in performance.
Research into taste and the placebo effect on sport performance are limited.
However, early research into the placebo effect provides compelling evidence of
the significant role the taste can have for inducing placebo effects and
influencing physiological responses. Ader and Cohen [118] administered a
distinctly flavoured drink followed by a toxic agent capable of suppressing the
immune system. After repeated administrations of the drink and toxic agent, the
taste of the drink alone resulted in an immunosuppression response. Similarly,
Olness and Ader [119] reported a clinical case study of a child with lupus
erythematosus (an autoimmune disease) after administering cyclophosphamide
paired with taste and smell stimuli similar to Ader and Cohen [118]. After initial
pairings of the drug with the sensory stimuli, the taste alone was administered
and the patient’s symptoms improved after 12 months. The publication of these
studies resulted in a proliferation of similar taste aversion research [120], which
has demonstrated the influence of taste and anticipatory responses in inducing
placebo effects.
It is likely that placebo effects of taste are mediated by neurobiological
pathways. While there are many neurobiological pathways associated with the
placebo effect, a large amount of research has investigated the role of the
endogenous opioid system [121]. This is not surprising given that μ-opioid
receptors located throughout the brain are critical for the reduction of pain [122].
Amanzio and Benedetti [123] exposed participants to a conditioning procedure of
1
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the opioid drug buprenorphine and measured pain tolerance and endogenous
opioid release in the brain. After repeated trials of the opioid drug, when
replaced with saline, pain tolerance significantly increased compared to baseline,
which was mediated by increase in activation of the endogenous opioid system.
Similar results have been reported elsewhere [124, 125] and highlight the
significant mediating role the endogenous opioid system has for inducing
placebo effects.
Like placebo effects, taste receptors can also mediate the release of endogenous
opioids [126, 127]. Although the magnitude of the effect can depend on age and
gender [128], the sweet taste of glucose and sucrose can modulate the production
of endogenous opioid release [129], whereas administration of sucrose directly to
the stomach has no effect [130]. This suggests that sweet taste can have analgesic
effects. However, where the ergogenic effects of taste tend to report pain-
relieving effects, placebo effects are often the result of similar mechanisms, e.g.
pain, fatigue and perception of effort [112, 113, 131]. While taste could have
direct neurobiological mechanisms, there is evidence that placebo effects can
mimic the neurobiological pathways of a treatment [132]. It could be suggested
that the same pathways activated by taste are also activated by the administration
of a placebo. We are by no means implying that the ergogenic effects of taste are
the result of a placebo effect, but we, like others [28, 133, 134], are suggesting
that the mechanisms in which a nutritional ergogenic aid exerts its effect is likely
to be a combination of both. As with most treatments and interventions on sport
performance, the ergogenic effect of taste will be influenced via the placebo
effect (see Beedie et al. [133]). It is likely that they are both components of a
self-regulatory system that act as signals to the brain for resource allocation,
which are likely to be mediated by neurobiological pathways, such as the
endogenous opioid system. However, there is a lack of research in sport
explicitly examining whether the ergogenic effect of taste and the placebo effect
activate shared or distinct mechanisms. To help develop knowledge and
understanding in this area beyond speculation, empirical research is needed that
examines whether the placebo effect of taste is partially or fully responsible for
its ergogenic effect.
Practical recommendations
Tastants have the potential to be employed as ergogenic strategies during sport
and exercise performance, with tentative evidence supporting the efficacy of
sweet [14], bitter [19], spicy [65], and cooling [11] tastants. However,
consideration of event demands, nutritional state of the athlete and athletes’
performance environment are strongly recommended to successfully employ
taste-related strategies in athletic settings. Developing taste-related strategies
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with regular input from athletes also allow for maximisation of other sensory
factors, such as colour and odour, which may confer further psychological and
performance benefits through placebo effects. At present, given the evidence
discussed, we can tentatively suggest that athletes undertaking aerobic endurance
and/or repeated high-intensity efforts may benefit from the use of sweet-tasting
carbohydrate or bitter-tasting beverages, with the addition of caffeine. Similar to
carbohydrate and bitter tastants, athletes may benefit from menthol
supplementation during endurance exercise, whereas capsaicin ingestion may be
of use during activities that are near maximal in nature. Menthol may be
administered as a mouth rinse at concentrations between 0.01% and 0.1% [29]
and can be employed throughout the exercise bout. Capsaicin may be ingested as
a capsule containing a 12 mg dose, 45 min prior to maximal effort exercise. All
strategies should be trialled prior to use in competition and the potential for GI
disturbance using a validated tool [135]. In using these beverages, there may be
additional advantages—and no obvious negatives—gained by the athlete from
rinsing the liquid around the oral cavity prior to ingestion. Furthermore,
augmented ergogenic effects may occur if the athlete recognises a taste as
performance-enhancing via expectancy and placebo effects [15].
Future research directions
Future research in taste and athletic performance should consider investigating
differences between tasting, swilling and ingesting, and their subsequent effects
upon performance; this is especially important given the emerging research that
ingestion of bitter tastants, such as quinine and caffeine, is required to maximise
their ergogenic effects above those demonstrated through mouth rinse only [15].
Each strategy exposes tastants to different densities and volumes of taste
receptors and may be accompanied by other sports nutrition strategies, so the
inclusion of tastants need to be weighed against established ergogenic strategies,
such as maintaining carbohydrate availability during an event. The optimal dose
of each tastant, including their physiological tolerance and associated side
effects, also represents an important practical avenue for future research.
Similarly, habituation to tastants is also worthy of investigation as we must
understand the time course of these strategies to maximise their efficacy. It is
acknowledged that there is likely a strong genetic underpinning to preference and
responses to tastes [136, 137]. Some work has already begun in caffeine [138,
139], carbohydrate [140, 141] and TRP-M8 [142], but understanding the genetic
contributions to liking, or tolerance for, thermal tastes and bitterness may confer
further benefits beyond athletic populations.
Conclusion
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This review synthesises the evidence from a variety of tastes that have shown
ergogenic promise with respect to athletic performance. This efficacy is not
limited to taste per se, but extends to the stimulation of targeted receptors in the
oral cavity and throughout the digestive tract, which relay signals pertaining to
energy availability and temperature to appropriate neural centres. Timing of
tastant application, dose and frequency of application likely require
personalisation to be most effective and can be enhanced or confounded by
factors that relate to the placebo effect.
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Providing an explanation for why this occurs is outside the scope of the paper, but we refer the
reader to the work of Humphrey [117] and Miller, Colloca and Kaptchuk [118], who offer a more
thorough explanation.
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