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The benefits of ingesting exogenous carbohydrate (CHO) during prolonged exercise performance are well established. A recent food technology innovation has seen sodium alginate and pectin included in solutions of multiple transportable CHO, to encapsulate them at pH levels found in the stomach. Marketing claims include enhanced gastric emptying and delivery of CHO to the muscle with less gastrointestinal distress, leading to better sports performance. Emerging literature around such claims was identified by searching electronic databases; inclusion criteria were randomized controlled trials investigating metabolic and/or exercise performance parameters during endurance exercise >1 hr, with CHO hydrogels versus traditional CHO fluids and/or noncaloric hydrogels. Limitations associated with the heterogeneity of exercise protocols and control comparisons are noted. To date, improvements in exercise performance/capacity have not been clearly demonstrated with ingestion of CHO hydrogels above traditional CHO fluids. Studies utilizing isotopic tracers demonstrate similar rates of exogenous CHO oxidation, and subjective ratings of gastrointestinal distress do not appear to be different. Overall, data do not support any metabolic or performance advantages to exogenous CHO delivery in hydrogel form over traditional CHO preparations; although, one study demonstrates a possible glycogen sparing effect. The authors note that the current literature has largely failed to investigate the conditions under which maximal CHO availability is needed; high-performance athletes undertaking prolonged events at high relative and absolute exercise intensities. Although investigations are needed to better target the testimonials provided about CHO hydrogels, current evidence suggests that they are similar in outcome and a benefit to traditional CHO sources.
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Carbohydrate Hydrogel Products Do Not Improve Performance
or Gastrointestinal Distress During Moderate-Intensity
Endurance Exercise
Andy J. King
Australian Catholic University
Joshua T. Rowe
University of Leeds
Louise M. Burke
Australian Catholic University and
Australian Institute of Sport
The benets of ingesting exogenous carbohydrate (CHO) during prolonged exercise performance are well established. A recent
food technology innovation has seen sodium alginate and pectin included in solutions of multiple transportable CHO, to
encapsulate them at pH levels found in the stomach. Marketing claims include enhanced gastric emptying and delivery of CHO to
the muscle with less gastrointestinal distress, leading to better sports performance. Emerging literature around such claims was
identied by searching electronic databases; inclusion criteria were randomized controlled trials investigating metabolic and/or
exercise performance parameters during endurance exercise >1 hr, with CHO hydrogels versus traditional CHO uids and/or
noncaloric hydrogels. Limitations associated with the heterogeneity of exercise protocols and control comparisons are noted. To
date, improvements in exercise performance/capacity have not been clearly demonstrated with ingestion of CHO hydrogels
above traditional CHO uids. Studies utilizing isotopic tracers demonstrate similar rates of exogenous CHO oxidation, and
subjective ratings of gastrointestinal distress do not appear to be different. Overall, data do not support any metabolic or
performance advantages to exogenous CHO delivery in hydrogel form over traditional CHO preparations; although, one study
demonstrates a possible glycogen sparing effect. The authors note that the current literature has largely failed to investigate the
conditions under which maximal CHO availability is needed; high-performance athletes undertaking prolonged events at high
relative and absolute exercise intensities. Although investigations are needed to better target the testimonials provided about
CHO hydrogels, current evidence suggests that they are similar in outcome and a benet to traditional CHO sources.
Keywords:encapsulated carbohydrate, glycogen, gut, sports nutrition, oxidation, sports drink
Recent interest in the 2-hr marathon (Caesar, 2019)has
focused attention on an important sports nutrition strategy; con-
sumption of carbohydrate (CHO) during exercise to contribute to
the substantial fuel costs of some endurance events. Events of
sufcient intensity and duration to be limited by CHO availability
benet from an exogenous CHO supply (Stellingwerff & Cox,
2014), with mechanisms including fuel provision once muscle
glycogen is depleted (Coyle et al., 1986), spared liver (Gonzalez
et al., 2015;Wallis et al., 2006)andmuscle(King et al., 2018;
Tsintzas et al., 1995,1996) glycogen use, and central nervous
system benets (Burke & Maughan, 2015). A sliding scale of
intake is recommended, according to event fuel needs and specic
mechanisms underpinning performance benets (Thomas et al.,
2016). Upper targets for fuel-demanding events (8090+ g·hr
CHO), which aim to maximize the contribution of exogenous
CHO to substrate use, are often challenged by the ability to
consume, tolerate, and absorb large amounts of CHO (de
Oliveira & Burini, 2014). Factors include the availability of
foods/drinks to meet CHO targets in practical amounts/volumes,
the effect of the mode and intensity of exercise on gastrointestinal
(GI) comfort and function (de Oliveira & Burini, 2009), the role of
specicgut training(Cox et al., 2010), and characteristics of the
CHO source. Here it has been shown that the use of CHO blends
(multiple transportable CHOsuch as glucose [G] and fructose
[F]) can maximize gut uptake via the use of different intestinal
transport mechanisms, assisting with substrate delivery and the
management of gut comfort (Jeukendrup, 2010).
Recently, specialized sports foods claiming to address such
factors via the use of hydrogel technologyhave become com-
mercially available (Sutehall et al., 2018). These supplements,
combining typical CHO sources with pectin (a soluble ber)
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King and Burke are with the Mary Mackillop Institute for Health Research,
Australian Catholic University, Melbourne, VIC, Australia. Burke is also with
the Australian Institute of Sport, Canberra, ACT, Australia. Rowe is with the
University of Leeds, Leeds, United Kingdom. King (
corresponding author.
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and alginate (a polymer derived from seaweed) undergo gelation on
contact with low pH solutions, such as stomach acid, to encapsulate
the CHO (Marciani et al., 2019). Enhanced rates of gastric empty-
ing could deliver this hydrogelto the small intestine where it
dissolves in the higher pH environment for absorption, leading to
reduced gut discomfort, enhanced muscle CHO delivery, and
performance benets (Figure 1). Indeed, according to testimonials,
the commercial product has been quickly adopted by elite athletes
(Sutehall et al., 2018) and publicized in sporting successes includ-
ing the 1:59 marathon project, leading to marketing claims that it is
the worlds fastest sports fuel(Maurten, 2020). Noting that this has
largely occurred in the absence of scientic validation of these
claims, we undertook a review of newly published investigations of
hydrogel CHO to determine whether they achieve better GI char-
acteristics, substrate delivery, and performance effects under exer-
cise conditions than traditional sports drinks and gels.
A search of electronic databases for studies published up to May
14, 2020 was independently completed by two authors (A. King/
J. Rowe), with the key methodological process and considerations
involved in including/excluding data summarized in Figure 2.
To be eligible for this review, studies were required to have
investigated a CHO hydrogel compound during prolonged, endur-
ance exercise dened as continuous running, cycling, triathlon,
rowing, swimming, and cross-country skiing greater than 1-hr dura-
tion. Studies with exercise durations lasting 1 hr or less were excluded
because CHO ingestion is unlikely to be benecial during shorter
duration exercise (Burke et al., 2011;Thomas et al., 2016). CHO
mouth rinse studies were also excluded as the primary mechanism
whereby performance is improved is neurological in origin.
The CHO hydrogel used could be a commercially available
product or a laboratory-manufactured solution, provided that the
active substance included as a gelling agent was known to encap-
sulate ingested CHO in the stomach. A control comparison/
condition was required to be a typical CHO control, matched for
CHO dose and type, or a placebo. Studies were included if they
reported data on one or more of physiological or performance
variables (Table 1). Review articles and case studies were excluded.
From the available studies, between-condition differences for
hydrogel and comparison products were calculated. Standardized
effect sizes (ES) were calculated using Hedgesgadjustment for
small samples with 95% condence intervals for the ES computed.
No statistical adjustments for ES were made for carryover effects,
since suitable washout periods were included in these crossover
trials. No assessment of publication bias was undertaken with the
low number of studies and the likely presence of heterogeneity; we
noted that this can affect the robustness of publication bias analysis
(Ioannidis & Trikalinos, 2007). Forest plots were produced to
provide a visual comparison of effects in studies measuring exer-
cise performance.
We located six studies (Table 1) which compared a CHO hydrogel
containing alginate and/or other gelling compounds with a nonca-
loric hydrogel placebo (n= 1) or CHO uids of matched CHO
(n= 5). Although CHO hydrogels were similar in composition,
containing a mixture of maltodextrin (MD) and F, total CHO
ranged from 68 to 132 g·hr
. Five of the six studies included a
matched condition for dose and type of CHO (i.e., MD + F uid)
and two studies included a G or MD only uid matched for CHO
dose. Therefore, four studies met guidelines for upper range CHO
Figure 1 Mechanisms of CHO hydrogel formation and delivery to the small intestine. Despite benets to gastric emptying with hydrogel-
encapsulated CHO, the rate-limiting step of exogenous CHO oxidation lies in the intestinal transport of monosaccharides. CHO = carbohydrate.
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intakes: 90 g·hr
from multiple transportable CHO sources
(Jeukendrup, 2010).
All studies were randomized controlled crossover trials. They
investigated trained male athletes (VO
max 5570 ml·kg
with the exception of Pettersson et al. (2019) and (Flood et al.,
2020), who included six female cross-country skiers (VO
59.9 ± 2.6 ml·kg
) and seven female cyclists (54.3 ±
12.3 ml·kg
). Exercise modes included cycling (four stud-
ies), running (one), and cross-country skiing (one). A period of
xed-intensity exercise was included in all protocols (90180 min)
with ve of the six studies then measuring exercise performance/
capacity using a time trial (three studies), time to exhaustion test
(one), or repeated sprint test (one). Each of the studies in which
performance was measured involved a preexercise meal according
to current recommendations (Burke et al., 2011) or a self-selected
CHO-richmeal (Flood et al., 2020). The only study undertaken
under fasting conditions (Barber et al., 2020) focused on exoge-
nous CHO oxidation as the primary outcome, which is not affected
by prior muscle glycogen content (Margolis et al., 2019). Between-
conditions comparisons remain valid despite the difference in
breakfast protocol to other studies.
Exercise Performance
Performance was similar with MD + F hydrogel, isocaloric MD + F
uids (Figure 3;Baur et al., 2019;Flood et al., 2020;McCubbin
et al., 2019;Mears et al., 2020b), or noncaloric hydrogel
(Pettersson et al., 2019). Relative performance changes between
CHO hydrogel and uids ranged between +1.05% and +3.8% but
were not statistically signicant (p<.05). The largest change
reported by Mears et al. (2020b) during a 20-min xed-work
time trial was a moderately higher workload (3.8% improvement,
ES = 0.51) with CHO hydrogel ingestion compared with the dose
matched MD + F control. All other performance effects were very
small (ES <0.10).
Physiological Measures
Exogenous CHO oxidation was measured in two studies, but only
one included a comparative CHO condition (Barber et al., 2020)
with exogenous CHO oxidation peaking at 1.1 ± 0.3 g·min
in both
the MD + F hydrogel and MD + F uid (Table 1). MD + G ingestion
resulted in a moderately lower oxidation rate (0.92 ± 0.3 g·min
Total exogenous CHO oxidation over the nal (second) hour of
running was not modied by MD + F hydrogel (48.25 ± 16.5 g vs.
50.25 ± 16.5 g in MD + F solution) but both were higher than
MD + G (41.25 ± 15.0 g). Pettersson et al. (2019) reported exoge-
nous CHO oxidation of 1.22 (0.891.66) g·min
with MD + F
hydrogel, indicating that a higher CHO dose (132
hydrogel may result in higher exogenous CHO utilization.
Total rates of CHO and fat oxidation during the steady-state
exercise varied between studies, a consequence of different exercise
intensities. Therefore, it is of interest to examine relative contribu-
tions to total fuel use (Figure 4) as well as absolute rates of oxidation
(Table 1). When comparing MD + F in hydrogel versus uid form,
divergent effects were reported. Mears et al. (2020b) and Baur et al.
(2019) found no differences in relative substrate contribution during
submaximal cycling at 50% W
but the nonsignicant increase in
fat oxidation (and decrease in CHO oxidation) reported by Baur et al.
(2019) is notable, and consistent with Barber et al. (2020). Flood
et al. (2020) also reported similar CHO and fat oxidation with CHO
and hydrogel ingestion during low-intensity cycling. However,
Baur et al. (2019) also noted lower absolute total CHO and fat
(to Mears et al. [2020b] in both conditions), despite similar ingestion
rates (68 and 78
). McCubbin et al. (2019) did not report
differences in substrate oxidation during steady-state running, and
neither CHO nor fat oxidation were modied by the hydrogel form
during a subsequent incremental test. Barber et al. (2020) however,
reported a reduced contribution of endogenous CHO during steady-
state running with hydrogel CHO. Glycogen contributed 60% of
total energy expenditure with MD + G and MD + F uids, but 50%
with MD+ F hydrogel. Differences in glycogen use were explained
by higher exogenous CHO oxidation in comparison with MD + G
uid, and increased fat oxidation in relation to MD + F uid
(Figure 4). Comparisons between studies employing different exer-
cise modalities for whole-body substrate utilization are difcult as
noted previously (Achten et al., 2003).
Figure 2 Methodology and review considerations. GI =
gastrointestinal; CHO = carbohydrate.
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Table 1 Studies Investigating CHO Hydrogel Formulations With Isocaloric CHO or Placebo Solutions
Study Participants Design/protocol
CHO Supplement
Ox (g·min
GI symptoms
Baur et al.
Nine male cyclists
(trained, VO
max =
55.5 ± 3.6 ml·kg
RCT; variable-
intensity cycling
(55 min SS @
50% W
4×2 min @ 80%
+ 5 min
@ 50% W
10 ×max sprint)
2 hr preexercise
(2025% daily
ERliquid meal
MD + F hydrogel 284 ± 51 W
n/a CHO: 1.50 ± 1.26
FAT: 0.25 ± 0.26
No signicant
Treatment ×Time
MD + F solution 281 ± 46 W
CHO: 1.53 ± 1.37
FAT: 0.19 ± 0.27
fullness vs. MD
(ES = 0.54)
MD solution 277 ± 48 W CHO: 1.40 ± 1.21
FAT: 0.26 ± 0.29
All 78 g·hr
1 L·hr
et al.
Nine male runners
(trained, VO
max =
59.0 ± 8.0 ml·kg
RCT; xed-inten-
sity running + TTE
(180 min
@ 60% VO
TTE: SS pace +
2 km·hr
/3 min)
2 hr preexercise MD + F hydrogel 744 ± 182 s
n/a CHO: 1.92 ± 0.30
FAT: n/a
11% vs. 22% inci-
dence of severe
symptoms hydrogel
vs. MD; F
24 kJ·kg
(1 g·kg
0.15 g·kg
MD + F solution
90 g·hr
0.57 L·hr
756 ± 187 s CHO: 1.95 ± 0.30
FAT: n/a
Breath H
not diff
et al.
12 elite CX skiers: six
males, six females
max = 69.1 ± 2.9 and
59.9 ±2.6 ml·kg
RCT; xed-inten-
sity CX skiing + TT
(120 min @
70% VO
1 hr preexercise MD + F hydrogel
132 g·hr
0.6 L·hr
239 ± 16 W
1.22 ± 0.4 CHO: 2.38 ± 0.25
FAT: 0.70 ± 0.06
No signicant
Treatment ×Time
1 g·kg
CHO PLA (noncaloric)
238 ± 16 W 0 CHO: 2.00 ± 0.26
FAT: 0.83 ± 0.08
Mears et al.
Eight cyclists
(well-trained, VO
max =
62.1 ± 6.9 ml·kg
RCT; xed-inten-
sity cycling + TT
(120 min @
50% W
2 hr preexercise MD + F hydrogel 1219 ± 84 s
n/a CHO: 2.59 ± 0.60
FAT: 0.42 ± 0.15
Fullness p= .02 in
1.5 g·kg
CHO MD + F solution
68 g·hr
0.5 L·hr
1,267 ± 102 s CHO: 2.56 ± 0.44
FAT: 0.42 ± 0.12
No other signicant
Treatment ×Time
et al.
Nine runners
(well-trained, VO
max =
63 ± 3.6 ml·kg
RCT; xed-inten-
sity running
(120 min @ 60%
Nil: 8 hr fast MD + F hydrogel n/a 1.1 ± 0.3 CHO: 2.60 ± 0.75
FAT: 0.47 ± 0.22
No signicant
Treatment ×Time
MD + F solution 1.1 ± 0.3 CHO: 3.04 ± 0.69
FAT: 0.31 ± 0.15
MD + G solution
90 g·hr
0.57 L·hr
0.9 ± 0.5 CHO: 2.88 ± 0.62
FAT: 0.43 ± 0.09
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Table 1 (continued)
Study Participants Design/protocol
CHO Supplement
Ox (g·min
GI symptoms
Flood et al.
14 cyclists: seven males,
seven females
max = 56.4 ±
7.6 ml·kg
; 54.3 ±
12.3 ml·kg
RCT; xed-inten-
sity cycling + TT
(90 min @ 45%
3 hr preexercise MD + F hydrogel 192 W
CHO: 1.73 ± 0.75
FAT: 0.21 ± 0.35
IFABP (end
CHO rich
MD + F solution 190 W
CHO: 1.70 ± 0.40
FAT: 0.27 ± 0.12
Water (500
vs. hydro-
gel [150
MD + F [by 70
90 g·h
in 0.78
168 W n/a CHO: 1.35 ± 0.40
FAT: 0.39 ± 0.15
Lactulose: Rham-
nose in MD + F
and hydrogel**
No signicant
treatment effects for
GI symptoms. Full-
ness in MD + F
and hydrogel
Note. RCT = randomized crossover trial; SS = steady state; TTE = time to exhaustion; TT = time trial; CHO = carbohydrate; ER = energy requirement; CX = cross-country (skiing); IFABP = Intestinal fatty acid binding protein;
MD = maltodextrin; F = fructose; G = glucose; GI = gastrointestinal; PLA = noncaloric placebo.
*Performance change not signicantly different (p>.05). Performance changes in Baur et al. (2019) are relative to MD condition and in Flood et al. (2020) relative to water. **Gastrointestinal effects signicantly different (p<.05) to
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Gastrointestinal discomfort was reported in all studies with
similar responses from the hydrogel trial. McCubbin et al. (2019)
reported a slightly, but not signicantly, higher overall incidence of
GI symptoms while running with MD + F uids than MD + F
hydrogel (22% vs. 11%). In cycling, Mears et al. (2020b) and
Baur et al. (2019) reported slightly increased stomach fullness with
CHO hydrogel ingestion but similarly, differences were not sig-
nicant. Fullness in Flood et al. (2020) did not differ between CHO
hydrogel and MD + F. Baur et al (2019) also reported moderately,
but not signicantly increased nausea with the hydrogel compared
with MD + F uids (ES = 0.53, p= .23). Data from Pettersson et al.
(2019) reported low levels of GI issues during skiing in cold
conditions in either trial, but a small, nonsignicant decrease in
stomach rumbling with the MD + F hydrogel in comparison with a
noncaloric hydrogel. In the only study to report GI data through
nonsubjective measures, Flood et al. (2020) found signicantly
higher intestinal fatty acid-binding protein and lactulose to rham-
nose ratio with placebo compared with both CHO hydrogel and
matched MD + F ingestion.
This is a timely investigation of the evidence that intake of hydrogel
encapsulations of multiple transportable CHO during prolonged
endurance exercise provides benets over traditional sports drinks,
in response to the recent interest in newly available commercial
hydrogel products. We summarized studies where hydrogels,
formed by combining MD + F with gelling agents such as alginate
and pectin, were compared with typical CHO uids containing
single or multiple CHO sources, or a noncaloric hydrogel treat-
ment. Despite marketing claims and lay media discussion about
MD + F products in hydrogel format, currently available studies
fail to show benets in terms of muscle oxidation of exogenous
CHO, GI comfort, or performance. The current literature, com-
prised of robust randomized controlled trials, is small and includes
nuances around total substrate oxidation and gut comfort due to
exercise mode and intensity, as well as total CHO intake. Further-
more, the conditions under which it is promoted to achieve its key
benets (high rates of CHO intake during prolonged exercise at
high absolute and relative intensities) have not been investigated,
potentially due to the challenge of involving elite competitors
within traditional research protocols and the technical challenges
of undertaking measurements of interest (e.g., gastric emptying,
tracer determined substrate oxidation) under these conditions.
While further studies with relevant protocols are needed to inves-
tigate the putative benets of these products, the present literature
fails to endorse the marketing claims.
Over the past 5 years, CHO-containing drinks that achieve
hydrogel encapsulation within the gut have become commer-
cially available, with claims that they achieve superior CHO
delivery to the muscle for lower GI distress, leading to perfor-
mance benets over traditional CHO-containing sports products
(Maurten, 2020;Sutehall et al., 2018). CHO hydrogel products
have attempted to improve on existing nutrition recommenda-
tions (use of CHO with multiple transporters [Jeukendrup, 2010]
and gut training [Jeukendrup, 2017]) to target the need for high-
performance athletes to achieve high CHO availability during
prolonged events conducted at high relative and absolute inten-
sities (Burke et al., 2019). Although there is evidence that these
products achieve gelation within the acidic stomach environ-
ment as claimed (Marciani et al., 2019;McCubbin et al., 2019),
subsequent effects on gastric emptying, intestinal absorption,
anddeliverytothemuscleduring exercise remain largely
untested. Our review summarized the available literature on
the use of these products during prolonged exercise in terms
of GI comfort, substrate utilization, and performance. The
scarcity and heterogeneity of study protocols prevents a meta-
analytical approach from producing meaningful results. How-
ever, in view of community interest and marketing claims, we
felt it was timely to collate the ndings of available studies in
narrative form to summarize the overall ndings and alert
researchers to the need for particular protocols.
Figure 3 Forest plot of standardized effects sizes and 95% condence intervals for exercise performance in studies comparing CHO hydrogel
formulations with isocaloric CHO or noncaloric placebo solutions. H = hydrogel; MD = maltodextrin; MD + F = maltodextrin + fructose; PLA = placebo;
H (MD + F) = hydrogel of MD + F; CHO = carbohydrate.
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The current literature involves studies of subelite athletes
(although one study of elite performers is noted [Pettersson
et al., 2019]), exercising over 23 hr at intensities of approximately
4570% VO
peak. Such protocols likely represent pragmatic
choices based on subject availability and the technical requirements
around the steady-state conditions needed to monitor muscle
substrate use during exercise (Robert et al., 1987). According to
our review, although the GI handling of these products has not been
directly measured, these studies have failed to nd evidence of
increased oxidation of exogenous CHO when MD + F is provided
in hydrogel form compared with conventional solutions. Indeed,
rates of exogenous CHO oxidation derived from
C isotopic tracer
techniques are in line with results of previous studies of traditional
CHO-containing uids (King et al., 2019;OBrien et al., 2013), or
in the case of studies in which direct comparison has been made
between CHO-matched uids and hydrogel products, no differ-
ences in exogenous CHO use has been detected (Barber et al.,
2020). Since the rate-limiting step of exogenous CHO oxidation
is believed to lie in the GI tract and not cellular glucose uptake
(Hawley et al., 1994), this indirectly indicates that CHO hydrogels
have not achieved a net benet to the gastric emptying/intestinal
CHO transport processes.
The studies published to date conrm previous knowledge that
whole-body CHO utilization is altered by the intake of CHO during
exercise (Pettersson et al., 2019) and by the choice of multiple
transportable CHO sources that increase the capacity for total
intestinal absorption (Barber et al., 2020;Baur et al., 2019). In
general, Figure 4suggests that hydrogel encapsulation per se does
not change total CHO oxidation during exercise (Baur et al., 2019;
Flood et al., 2020;McCubbin et al., 2019;Mears et al., 2020b).
However, Barber et al. (2020) reported a decrease in endogenous
CHO utilization and increase in fat oxidation when high rates of
CHO intake were consumed in hydrogel form versus uid. Muscle
glycogen sparing effects have been reported in several studies of
CHO intake during endurance exercise, but performance improve-
ments have not been consistently observed (Newell et al., 2014).
Previous work from our group (King et al., 2018) and others (Smith
et al., 2010) has shown that the muscle glycogen response to CHO
ingestion is dose dependent. Precise mechanisms to explain this
effect have not been investigated, but likely sit within the cellular
ux through the glycolytic pathway and the interaction of exoge-
nous glucose and glucosyl units liberated from glycogen at glu-
cose-6-phosphate. Exogenous CHO more consistently reduces
liver glycogen use as long as the ingested dose is sufcient to
inhibit hepatic glycogenolysis and glucose output (Gonzalez &
Betts, 2019). However, liver glycogen capacity is much smaller
than muscle (100 g vs. 400500 g) and complete liver glycogen
sparing during exercise has only been reported with an extremely
high CHO dose (Jeukendrup et al., 1999). The ingested doses in the
reviewed studies cover a wide range, and only one study estimated
whole-body endogenous glycogen utilization using expired
tracer methods, which do not account for specic liver and muscle
contributions; conclusions around a dose effect with CHO hydro-
gels are not possible at this stage. However, if an event requires
maximized CHO availability, recommendations to saturate intesti-
nal CHO transporters should remain if athletes tolerate these doses
in terms of GI distress.
As has been the case in previous investigations of CHO
feeding during exercise, methodological differences between stud-
ies do not allow rm interstudy comparisons. Factors such as CHO
Figure 4 Comparison of relative contributions to energy expenditure from fat (black bars) and carbohydrate (white bars) with maltodextrin and
fructose (MD + F) ingestion in uid and hydrogel form. Exogenous (dotted bars) and endogenous (hashed bars) contributions shown where data were
available. MD + F = maltodextrin + fructose; CHO = carbohydrate.
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dose, as well as timing, exercise intensity, mode and duration,
prefeeding state, and potentially training status create differences in
outcomes. Although such variability creates difculty in piecing
together an emerging literature, it is important to recognize that
many of these factors may be xed or characteristic of specic
sporting events. Further studies, particularly those using multiple
conditions within the same investigation, might help to isolate any
conditions under which hydrogel CHO might provide an advan-
tage. Exercise intensity has important implications for intestinal
absorption due to the diversion of splanchnic blood ow at higher
intensities (ter Steege & Kolkman, 2012). Therefore, potential
mechanistic benets of CHO hydrogels in terms of GI tolerance
and absorption may only be observed in the higher intensity
domains, presenting an opportunity for future research. To date,
only one study (Pettersson et al., 2019) has investigated what may be
considered higher intensity exercise. Running also utilizes less
localized muscle recruitment compared with cycling, resulting in
increased surface area blood ow and a greater reduction of
splanchnic blood ow (de Oliveira et al., 2014). Similar responses
are likely in cross-country skiing given the whole-body nature of the
sport and may even demand higher CHO utilization (Losnegard
et al., 2014). While body mass is not considered a methodological
factor for exogenous CHO oxidation (Jeukendrup, 2010), the com-
bination of differences in exercise mode and intensity in the
reviewed studies does not allow for rm extrapolations to higher
intensity exercise, which may also benet further from optimal, that
is, at intestinal saturation, CHO dosing. Due to the increased duration
of training and competition, cyclists may be at an advantage over
runners if habituated to CHO intake. Increased CHO exposure
causes a gut trainingeffect (Cox et al., 2010), leading to enhanced
GI tolerance of ingested CHO during exercise. Gut tolerance is
therefore a further methodological factor that differentiates between
exercise modality and may mean potential GI benets to CHO
hydrogels may be more likely in individuals with lower natural CHO
tolerance or with less habitual CHO gut training. This would serve as
a useful consideration or screening tool in future study design.
Typically, the intake of solutions with high CHO content
during prolonged exercise delays gastric emptying and is associ-
ated with higher incidence of GI distress (Rehrer et al., 1992). A
positive nding from this review is that MD + F hydrogel formula-
tions were generally well tolerated across the range of doses and
exercise protocols that were examined. However, hydrogel solu-
tions did not improve GI tolerance per se above comparable CHO
sources in traditional uid form. It remains to be seen if they
systematically reduce GI symptoms at higher doses approaching
and above intestinal saturation, due to specic interaction with the
digestive system. Reports of a slight increase in gastric fullness
associated with the hydrogel are of interest (Baur et al., 2019), since
even if there is a subsequent increase in gastric emptying associated
with the formation of the gel, it may create an initial sensation of
fullness. Quantitative measures of GI barrier function and damage
reported by Flood et al. (2020) evidence that CHO hydrogels do not
provide a further protective effect to the intestinal membrane over
typical CHO ingestion. These data do however, conrm the
preventative role of CHO for enterocyte injury and small intestine
permeability during endurance exercise (Snipe et al., 2017).
Although an enhancement of gastric emptying is the mecha-
nism most heavily marketed in support of the use of the hydrogel
sports drinks, the importance of gastric emptying in the whole
process of delivering CHO from the mouth to the muscle mito-
chondria, and any benets achieved by hydrogels, are difcult to
ascertain. So far, the available evidence is limited to a report by
Sutehall et al. (2020) that a commercially available MD + F
hydrogel increased gastric emptying compared with G + F and
MD + F solutions when consumed as a bolus at rest, with time to
empty half the drink being nearly twice as fast for MD + F hydrogel
(21 min) than its uid counterpart (37 min). Despite signicantly
less volume remaining in the stomach at 30 min, differences
became increasingly smaller thereafter (Sutehall et al., 2020). Since
none of the currently available studies have attempted to directly
measure gastric emptying during exercise, it is not possible to
comment on what occurs under these circumstances. However,
according to the general literature, gastric emptying is not consid-
ered to be the rate-limiting step in determining the availability of
exogenous fuels consumed during exercise (see review by
Rowlands et al. [2015]) and its measurement includes artifacts
and practical difculties. Furthermore, without using complex
invasive measures (Shi et al., 1995), intestinal absorption cannot
be directly measured; therefore, the endpoint of muscle CHO
oxidation is used to reect the contribution of a combination of
gut processes between consumption and delivery to the mitochon-
dria. The evidence collected from the currently available studies
does not show clear evidence of differences in the overall process.
Even if hydrogel-encapsulated CHO can be shown to have
different gut characteristics per se, the effects of the amount,
timing, and pattern of intake of CHO sources on gastric emptying
are among the many interacting factors that should be considered
in the current story. This is of interest since in many sporting
events, the pattern of intake is dictated by the availability of uids
at breaks or feed stations rather than continuous or spontaneous
access. Recent work by Mears et al. (2020a) reported that mean
and peak exogenous CHO oxidation is altered slightly (but
signicantly) by CHO timing, with better outcomes associated
with consuming sources every 20 min compared with 5-min
intervals. Meanwhile, Menzies et al. (2020) reported better endur-
ance when CHO intake commenced early during a running
protocol than later delivery. Therefore, future research should
systematically investigate conditions under which a hydrogel
CHO might be used. Although this will involve a large number
of permutations of characteristics, we note in particular, that
scenarios from which current testimonials about the use of
hydrogels have emanated have not been investigated. These
include use by elite athletes in events such as the marathon
requiring high CHO availability from endogenous and exogenous
sources to fuel prolonged exercise (2 hr+) of high relative and
absolute intensities (Maurten, 2020;Sutehall et al., 2018). Here,
the combination of issues such as high fuel requirement, high risk
of gut distress, and a practical requirement for small uid volumes
intersect, making them a priority for study.
In conclusion, a small number of studies have investigated the
use of commercially available CHO hydrogels to deliver CHO
during exercise. So far, data do not support the claimed benets of
enhanced CHO delivery to the muscle, reduced GI distress, and
better performance compared with the use of traditional CHO
solutions. Future research should focus on dose and timing of
hydrogel ingestion, higher exercise intensities where GI issues are
more prevalent and CHO absorption more greatly impaired, and
further mechanistic insights around endogenous CHO responses.
Athletes may continue to use CHO hydrogels to meet current
guidelines for endurance nutrition practices if this is their prefer-
ence. While no disadvantages around the use of these specialized
sports products appear to be present, based on current evidence,
they do not confer metabolic or performance advantages over
typical CHO ingestion strategies.
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All authors contributed to the preparation of this manuscript. The authors
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... Emerging research suggests that the ingestion of a CHO, sodium alginate, and pectin solution can enhance the rate of gastric emptying compared with a standard nonhydrogel CHO solution (28). However, no study to date (29), including running (30,31), has reported a benefit to exercise performance, total whole-body substrate metabolism, exogenous CHO oxidation, or GI symptoms when CHO was consumed as a hydrogel during endurance exercise. These findings could be related to the mode of exercise and the exercise intensities (45%-60% V O 2max ) studied. ...
... (GraphPad Software, La Jolla, CA). Eleven trained male runners were recruited for this study, providing 92% power to detect differences in performance, with an expected mean difference of 1.6% between CHO hydrogel and nonhydrogel (29), assuming an SD of 1.43% at an alpha of 0.05. ...
... The novel performance effects observed in the present study when ingesting CHO hydrogel while running conflict with previous evidence that have failed to detect a performance benefit across cycling, cross-country skiing, and running (29). The reasons for the discrepancy are unclear, but it may relate to differences in exercise intensity, duration, CHO type and dose, training status, exercise mode, or the performance test used. ...
Full-text available
Purpose: Beneficial effects of carbohydrate (CHO) ingestion on exogenous CHO oxidation and endurance performance require a well-functioning gastrointestinal (GI) tract. However, GI complaints are common during endurance running. This study investigated the effect of a CHO solution-containing sodium alginate and pectin (hydrogel) on endurance running performance, exogenous and endogenous CHO oxidation and GI symptoms. Methods: Eleven trained male runners, using a randomised, double-blind design, completed three 120-minute steady state runs at 68% V[Combining Dot Above]O2max, followed by a 5-km time-trial. Participants ingested 90 g·h-1 of 2:1 glucose:fructose (13C enriched) either as a CHO hydrogel, a standard CHO solution (non-hydrogel), or a CHO-free placebo during the 120 minutes. Fat oxidation, total and exogenous CHO oxidation, plasma glucose oxidation and endogenous glucose oxidation from liver and muscle glycogen were calculated using indirect calorimetry and isotope ratio mass spectrometry. GI symptoms were recorded throughout the trial.RESULTS: Time-trial performance was 7.6% and 5.6% faster after hydrogel ([minutes:seconds]19:29 ± 2:24; p < 0.001) and non-hydrogel (19:54 ± 2:23, p = 0.002), respectively, versus placebo (21:05 ± 2:34). Time-trial performance after hydrogel was 2.1% faster (p = 0.033) than non-hydrogel. Absolute and relative exogenous CHO oxidation was greater with hydrogel (68.6 ± 10.8 g, 31.9 ± 2.7%; p = 0.01) versus non-hydrogel (63.4 ± 8.1 g, 29.3 ± 2.0%; p = 0.003). Absolute and relative endogenous CHO oxidation were lower in both CHO conditions compared with placebo (p < 0.001), with no difference between CHO conditions. Absolute and relative liver glucose and muscle glycogen oxidation were not different between CHO conditions. Total GI symptoms were not different between hydrogel and placebo, but GI symptoms was higher in non-hydrogel compared with placebo and hydrogel (p < 0.001). Conclusion: Ingestion of glucose and fructose in hydrogel form during running benefited endurance performance, exogenous CHO oxidation and GI symptoms, compared with a standard CHO solution.
... While there is yet to be any studies specifically aimed at investigating the potential GID reducing effects, a growing number of studies have been performed with the aim to identify any potential ergogenic effects associated with CHO ingestion with sodium alginate and pectin. Two narrative reviews have emerged discussing the potential efficacy and effectiveness of this development [17,18], although both relied on non-systematic approaches to review the literature. While this may be useful for interpreting the literature, a more reliable and accurate method, using quantitative data where appropriate, should be used to make conclusions on the published literature. ...
... The most obvious conclusion is that across the range of CHO intake rates (66-90 g hr −1 ), exercise intensities (45-71% V O 2 max ), exercise duration (98-180 min) and exercise modality (cycling or running), the addition of sodium alginate and pectin did not alter the GID response of the participants [24][25][26][28][29][30]. However, to conclude that the addition of sodium alginate and pectin is not beneficial for reducing GID experienced by participants during exercise, as has been done multiple times [17,24,26,28], is not supported by the literature. This conclusion has been made on the evidence that there were no significant differences in GID between a CHO beverage with or without additional sodium alginate and pectin. ...
Full-text available
Introduction Scientific and public interest in the potential ergogenic effects of sodium alginate added to a carbohydrate (CHO) beverage has increased in the last ~ 5 years. Despite an extensive use of this technology by elite athletes and recent research into the potential effects, there has been no meta-analysis to objectively elucidate the effects of adding sodium alginate to a CHO beverage on parameters relevant to exercise performance and to highlight gaps in the literature. Methods Three literature databases were systematically searched for studies investigating the effects of sodium alginate added to CHO beverage during prolonged, endurance exercise in healthy athletes. For the systematic review, the PROSPERO guidelines were followed, and risk assessment was made using the Cochrane collaboration’s tool for assessing the risk of bias. Additionally, a random-effects meta-analysis model was used to determine the standardised mean difference between a CHO beverage containing sodium alginate and an isocaloric control for performance, whole-body CHO oxidation and blood glucose concentration. Results Ten studies were reviewed systematically, of which seven were included within the meta-analysis. For each variable, there was homogeneity between studies for performance (n = 5 studies; I² = 0%), CHO oxidation (n = 7 studies; I² = 0%) and blood glucose concentration (n = 7 studies; I² = 0%). When compared with an isocaloric control, the meta-analysis demonstrated that there is no difference in performance (Z = 0.54, p = 0.59), CHO oxidation (Z = 0.34, p = 0.71) and blood glucose concentration (Z = 0.44, p = 0.66) when ingesting a CHO beverage containing sodium alginate. The systematic review revealed that several of the included studies did not use sufficient exercise intensity to elicit significant gastrointestinal disturbances or demonstrate any ergogenic benefit of CHO ingestion. Risk of bias was generally low across the included studies. Conclusions This systematic review and meta-analysis demonstrate that the current literature indicates no benefit of adding sodium alginate to a CHO beverage during exercise. Further research is required, however, before firm conclusions are drawn considering the range of exercise intensities, feeding rates and the apparent lack of benefit of CHO reported in the current literature investigating sodium alginate.
... During training sessions, CHO-containing drinks were provided according to diet intervention; CON received 30 g·h −1 of a glucose:fructose [2:1] solution (Isoactive, PowerBar, Berkeley, CA, USA), while MAX was required to build up to the highest tolerable rate within the range of 60-90 g·h −1 over the period. In a small tweak of the protocol used in Study 1, the MAX group was provided with a CHO hydrogel glucose:fructose sports drink (Maurten, Sweden) due to athlete interest in claims that this product might enhance CHO delivery and mitigate GIS [38]. The post-intervention trial was undertaken following 3-day of CHO loading; in the case of the CON group, this protocol was identical to the pre-intervention trial. ...
... We note that the hydrogel drink is marketed with claims of an enhancement of gastric emptying, gastrointestinal comfort, CHO delivery, and performance [51]. Although these claims were not supported in the earlier literature [38], more recent studies have reported some modest benefits [52][53][54], including enhanced gastric comfort [53] in comparison to traditional CHO drinks, albeit during non-exercise protocols that do not mimic sport [52] or did not use contemporary, validated tools to assess GIS [53]. In the current protocol involving runners, although there were some increases in gastrointestinal discomfort across exercise, there were no differences in the post-intervention trial between the CON and MAX groups, despite the 3-fold increase in the rate of CHO intake in the latter. ...
Full-text available
We implemented a multi-pronged strategy (MAX) involving chronic (2 weeks high carbohydrate [CHO] diet + gut-training) and acute (CHO loading + 90 g·h −1 CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON) in two groups of athletes. Nineteen elite male race walkers (MAX: 9; CON:10) undertook a 26 km race-walking session before and after the respective interventions to investigate gastrointestinal function (absorption capacity), integrity (epithelial injury), and symptoms (GIS). We observed considerable individual variability in responses, resulting in a statistically significant (p < 0.001) yet likely clinically insignificant increase (∆ 736 pg·mL −1) in I-FABP after exercise across all trials, with no significant differences in breath H 2 across exercise (p = 0.970). MAX was associated with increased GIS in the second half of the exercise, especially in upper GIS (p < 0.01). Eighteen highly trained male and female distance runners (MAX: 10; CON: 8) then completed a 35 km run (28 km steady-state + 7 km time-trial) supported by either a slightly modified MAX or CON strategy. Inter-individual variability was observed, without major differences in epithelial cell intestinal fatty acid binding protein (I-FABP) or GIS, due to exercise, trial, or group, despite the 3-fold increase in exercise CHO intake in MAX post-intervention. The tight-junction (claudin-3) response decreased in both groups from pre-to post-intervention. Groups achieved a similar performance improvement from pre-to post-intervention (CON = 39 s [95 CI 15-63 s]; MAX = 36 s [13-59 s]; p = 0.002). Although this suggests that further increases in CHO availability above current guidelines do not confer additional advantages, limitations in our study execution (e.g., confounding loss of BM in several individuals despite a live-in training camp environment and significant increases in aerobic capacity due to intensified training) may have masked small differences. Therefore, athletes should meet the minimum CHO guidelines for training and competition goals, noting that, with practice, increased CHO intake can be tolerated, and may contribute to performance outcomes.
... A recent review highlighted the lack of evidence for benefits from the use of sodium alginate and pectin added to a CHO beverage on physiological or GID symptoms during moderate intensity exercise (36). Current, mechanism-driven research has shown that a hydrogel can form around a CHO (37), which occurs in vivo (18) and subsequently enhances GE (19). ...
... Current, mechanism-driven research has shown that a hydrogel can form around a CHO (37), which occurs in vivo (18) and subsequently enhances GE (19). Following this, however, there have been several studies which showed no differences from "standard" CHO beverages when comparing various physiological markers (e.g., ExCHO, wholebody oxidation rates and blood metabolites) and subjective markers (e.g., RPE and GID symptoms) [as reviewed elsewhere (36)]. The lack of any clear benefit when ingesting CHO with additional sodium alginate and pectin may be due to several factors. ...
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PurposeThe purpose of this study is to quantify the effect of adding sodium alginate and pectin to a carbohydrate (CHO) beverage on exogenous glucose (ExGluc) oxidation rate compared with an isocaloric CHO beverage.Methods Following familiarization, eight well-trained endurance athletes performed four bouts of prolonged running (105 min; 71 ± 4% of VO2max) while ingesting 175 mL of one of the experimental beverages every 15 min. In randomized order, participants consumed either 70 g.h−1 of maltodextrin and fructose (10% CHO; NORM), 70 g.h−1 of maltodextrin, fructose, sodium alginate, and pectin (10% CHO; ENCAP), 180 g.h−1 of maltodextrin, fructose, sodium alginate, and pectin (26% CHO; HiENCAP), or water (WAT). All CHO beverages had a maltodextrin:fructose ratio of 1:0.7 and contained 1.5 g.L−1 of sodium chloride. Total substrate oxidation, ExGluc oxidation rate, blood glucose, blood lactate, serum non-esterified fatty acid (NEFA) concentration, and RPE were measured for every 15 min. Every 30 min participants provided information regarding their gastrointestinal discomfort (GID).ResultsThere was no significant difference in peak ExGluc oxidation between NORM and ENCAP (0.63 ± 0.07 and 0.64 ± 0.11 g.min−1, respectively; p > 0.5), both of which were significantly lower than HiENCAP (1.13 ± 0.13 g.min−1, p < 0.01). Both NORM and HiENCAP demonstrated higher total CHO oxidation than WAT from 60 and 75 min, respectively, until the end of exercise, with no differences between CHO trials. During the first 60 min, blood glucose was significantly lower in WAT compared with NORM and HiENCAP, but no differences were found between CHO beverages. Both ENCAP and HiENCAP demonstrated a higher blood glucose concentration from 60–105 min than WAT, and ENCAP was significantly higher than HiENCAP. There were no significant differences in reported GID symptoms between the trials.Conclusions At moderate ingestion rates (i.e., 70 g.h−1), the addition of sodium alginate and pectin did not influence the ExGluc oxidation rate compared with an isocaloric CHO beverage. At very high ingestion rates (i.e., 180 g.h−1), high rates of ExGluc oxidation were achieved in line with the literature.
... The latter include glucose-fructose mixtures that utilize different gut transporters. They can also increase total intestinal absorption and rates of muscle oxidation of ingested CHO (Jeukendrup, 2010), CHO encapsulated with pectin and alginate to form a 'hydrogel' (King et al., 2020) and CHO molecules or modified 24hr pre-event fuelling @ 7-12g per kg BM Targets vary according to depletion from pervious exercise and fuel needs of event ...
... There is often a mismatch between the testimonials for these products and the results of laboratory research. For example, although commercial hydrogel products have been quickly adopted by elite athletes (Sutehall et al., 2018) and publicized as contributing to sporting successes including the 1:59 marathon project (Maurten, 2020), the first wave of studies failed to find evidence of faster gastric emptying, greater gut comfort or muscle fuel delivery or superior performance support (King et al., 2020). In fairness, however, protocols involving elite athletes running at very high absolute and relative speeds have not been sufficiently investigated. ...
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New findings: What is the topic of this review? The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them. What advances does it highlight? A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event-specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real-life sport for optimal implementation. Abstract: High-performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low-carbohydrate high-fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst-driven drinking) to fluid intake.
... The development of food technologies and the drive for advancement in metabolic performance has resulted in new applications of isotopic tracer methods. The development of hydrogel technology for carbohydrate ingestion in sport and exercise, for example, has led to anecdotal and empirical evidence for increased metabolic handling of carbohydrate (King et al., 2020;Sutehall et al., 2018). Similarly, the inclusion of modified starches (Baur & Saunders, 2021;Baur et al., 2016) to adjust osmolality and glycemic index of ingested substrates means consideration of appropriate isotopic Figure 4 -Example of isotope tracer methods of carbohydrate metabolism, where a [6,6-2 H 2 ]-glucose intravenous infusion is combined with [U-13 C]carbohydrate (e.g., glucose and/or fructose) ingestion. ...
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Isotopic tracers can reveal insights into the temporal nature of metabolism and track the fate of ingested substrates. A common use of tracers is to assess aspects of human carbohydrate metabolism during exercise under various established models. The dilution model is used alongside intravenous infusion of tracers to assess carbohydrate appearance and disappearance rates in the circulation, which can be further delineated into exogenous and endogenous sources. The incorporation model can be used to estimate exogenous carbohydrate oxidation rates. Combining methods can provide insight into key factors regulating health and performance, such as muscle and liver glycogen utilization, and the underlying regulation of blood glucose homeostasis before, during, and after exercise. Obtaining accurate, quantifiable data from tracers, however, requires careful consideration of key methodological principles. These include appropriate standardization of pretrial diet, specific tracer choice, whether a background trial is necessary to correct expired breath CO 2 enrichments, and if so, what the appropriate background trial should consist of. Researchers must also consider the intensity and pattern of exercise, and the type, amount, and frequency of feeding (if any). The rationale for these considerations is discussed, along with an experimental design checklist and equation list which aims to assist researchers in performing high-quality research on carbohydrate metabolism during exercise using isotopic tracer methods.
... One laboratory-based study has confirmed improved running performance, greater carbohydrate oxidation and lower GI symptoms following hydrogel ingestion compared with a standard CHO solution (Rowe et al., 2022). However, other laboratory-based studies have not reported any of these advantages following hydrogel ingestion compared to the ingestion of carbohydrate-electrolyte sport beverages (Baur et al., 2019;King et al., 2020;McCubbin et al., 2020). Nevertheless, it is a great example of sports nutrition innovation specific to the needs of the sport in the field. ...
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Sports nutrition is a relatively new discipline; with ~100 published papers/year in the 1990s to ~3,500+ papers/year today. Historically, sports nutrition research was primarily initiated by university-based exercise physiologists who developed new methodologies that could be impacted by nutrition interventions (e.g., carbohydrate/fat oxidation by whole body calorimetry and muscle glycogen by muscle biopsies). Application of these methods in seminal studies helped develop current sports nutrition guidelines as compiled in several expert consensus statements. Despite this wealth of knowledge, a limitation of the current evidence is the lack of appropriate intervention studies (e.g., randomized controlled clinical trials) in elite athlete populations that are ecologically valid (e.g., in real-life training and competition settings). Over the last decade, there has been an explosion of sports science technologies, methodologies, and innovations. Some of these recent advances are field-based, thus, providing the opportunity to accelerate the application of ecologically valid personalized sports nutrition interventions. Conversely, the acceleration of novel technologies and commercial solutions, especially in the field of biotechnology and software/app development, has far outstripped the scientific communities' ability to validate the effectiveness and utility of the vast majority of these new commercial technologies. This mini-review will highlight historical and present innovations with particular focus on technological innovations in sports nutrition that are expected to advance the field into the future. Indeed, the development and sharing of more “big data,” integrating field-based measurements, resulting in more ecologically valid evidence for efficacy and personalized prescriptions, are all future key opportunities to further advance the field of sports nutrition.
Vigorous or prolonged exercise poses a challenge to gastrointestinal system functioning and is associated with digestive symptoms. This narrative review addresses 1) the potential of dietary supplements to enhance gut function and reduce exercise-associated gastrointestinal symptoms and 2) strategies for reducing gastrointestinal-related side effects resulting from popular sports supplements. Several supplements, including probiotics, glutamine, and bovine colostrum, have been shown to reduce markers of gastrointestinal damage and permeability with exercise. Yet, the clinical ramifications of these findings are uncertain, as improvements in symptoms have not been consistently observed. Among these supplements, probiotics modestly reduced exercise-associated gastrointestinal symptoms in a few studies, suggesting they are the most evidenced-based choice for athletes looking to manage such symptoms through supplementation. Carbohydrate, caffeine, and sodium bicarbonate are evidence-based supplements that can trigger gastrointestinal symptoms. Using glucose-fructose mixtures is beneficial when carbohydrate ingestion is high (>50 g/h) during exercise, and undertaking multiple gut training sessions prior to competition may also be helpful. Approaches for preventing caffeine-induced gastrointestinal disturbances include using low-to-moderate doses (<500 mg) and avoiding/minimizing exacerbating factors (stress, anxiety, other stimulants, fasting). Adverse gastrointestinal effects of sodium bicarbonate can be avoided by using enteric-coated formulations, low doses (0.2 g/kg), or multi-day loading protocols.
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Cycling is a sport characterised by high training load and adequate nutrition is essential for training and race performance. With increased popularity of indoor trainers, cyclists have a unique opportunity to practice and implement key nutritional strategies. This study aimed to assess carbohydrate intake and nutrition knowledge of cyclists training or racing in this unique scenario for optimising exercise nutrition. A mixed-methods approach consisting of a multiple-pass self-report food recall and questionnaire was used to determine total carbohydrate intake pre, during and post training or racing using a stationary trainer and compared to current guidelines for endurance exercise. Sub-analyses were also made for higher ability cyclists (> ⁻¹ functional threshold power), races vs. non-races and ‘key’ training sessions. Mean CHO intake pre and post ride was 0.7±0.6 and 1.0±0.8 g.kgBM ⁻¹ and 39.3±27.5 g.h ⁻¹ during. Carbohydrate intake was not different for races (pre/during/post, p=0.31, 0.23, 0.18 respectively), ‘key sessions’ (p=0.26, 0.89, 0.98), or higher ability cyclists (p=0.26, 0.76, 0.45). The total proportion of cyclists who failed to meet CHO recommendations was higher than those who met guidelines (pre=79%, during=86%, post=89%). Cyclists training or racing indoors do not meet current CHO recommendations for cycling performance. Due to the short and frequently high-intensity nature of some sessions, opportunity for during exercise feeding may be limited or unnecessary.
Rationale: The traditional method to measure 13CO2 enrichment in breath involves isotope ratio mass spectrometry (IRMS) and has several limitations such as cost, extensive training and large space requirements. Here we present the validity and reliability data of an isotope ratio infrared spectrometer (IRIS) based method developed to combat these limitations. Methods: Eight healthy male runners performed 105 min of continuous running on a motorised treadmill while ingesting various carbohydrate beverages enriched with 13C and expired breath samples obtained every 15 min in triplicate. A total of 213 breath samples were analysed using both methods, while 212 samples were repeated using IRIS to determine test-retest reliability. Bland-Altman analysis was performed to determine systematic and proportional bias, and intraclass correlation coefficient (ICC) and coefficient of variation (CV) to assess level of agreement and magnitude of error. Results: The IRIS method demonstrated a small but significant systematic bias to overestimate δ13CO2 (0.18‰; p<0.05) compared with IRMS, without any proportional bias or heteroscedasticity and a small CV% (0.5%). There was a small systematic bias during the test-retest of the IRIS method (-0.07‰; p<0.05), no proportional bias, an excellent ICC (1.00) and small CV% (0.4%). Conclusions: The use of the Delta Ray IRIS to determine 13C enrichment in expired breath samples captured during exercise has excellent validity and reliability when compared with the gold standard IRMS.
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Purpose: To compare the effects of consuming a 16% maltodextrin+fructose+pectin alginate (MAL+FRU+PEC+ALG) drink against a nutrient matched maltodextrin-fructose (MAL+FRU) drink on enterocyte damage and gastrointestinal permeability after cycling in hot and humid conditions. Methods: Fourteen recreational cyclists (7 men) completed three experimental trials in a randomized placebo-controlled design. Participants cycled for 90 min (45% VO2max) and completed a 15 min time-trial in hot (32°C) humid (70% relative humidity) conditions. Every 15-minutes cyclists consumed 143 mL of either (1) water; (2) MAL+FRU+PEC+ALG (90g w/v), (3) - a ratio-matched MAL+FRU drink also (90g w/v). Blood was sampled before and after exercise and gastrointestinal (GI) permeability determined by serum measurements of intestinal fatty acid-binding protein (IFABP) and the percent ratio of lactulose (5g) to rhamnose (2g) recovered in post-exercise urine. Results: Compared to WATER, IFABP decreased by 349±67pg.mL-1 with MAL+FRU+PEC+ALG (p=0.007), and by 427±56pg.mL-1 with MAL+FRU (p=0.02). GI permeability was reduced in both the MAL+FRU+PEC+ALG (by 0.019±0.01, p = 0.0003) and MAL+FRU (by 0.014±0.01, p = 0.002) conditions relative to WATER. Conclusion: Both CHO beverages attenuated GI barrier damage to a similar extent relative to water. No metabolic, cardiovascular, thermoregulatory or performance differences were observed between the CHO beverages. Novelty bullets • Consumption of multiple-transportable CHO, with or without hydrogel properties, preserves GI barrier integrity and reduces enterocyte damage during prolonged cycling in hot-humid conditions.
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The addition of gelling polysaccharides to sport-drinks may provide improved tolerability of drinks with high concentration of digestible carbohydrates (CHO), otherwise known to increase the risk of gastro-intestinal complaints among athletes under prolonged exercise. The physico-chemical properties of a drink containing 14 % wt of digestible CHO (0.7:1 fructose and maltodextrin-ratio), 0.2 % wt of HM-pectin / alginate and 0.06 % wt. sodium chloride were examined under in vitro gastric conditions using rheology and large deformation testing. The in-vivo gelling behaviour of the drink was studied using magnetic resonance imaging of subjects at rest together with blood glucose measurements. The in-vivo results confirm gelation of the test drink, with no gel remaining in the stomach at 60 min and blood glucose values were similar to control. The physico-chemical characterisation of the acidified test drink confirms the formation of a weak gel through which low Mw CHO can diffuse.
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Abstract Background Whilst the ergogenic effects of carbohydrate intake during prolonged exercise are well-documented, few investigations have studied the effects of carbohydrate ingestion during cross-country skiing, a mode of exercise that presents unique metabolic demands on athletes due to the combined use of large upper- and lower-body muscle masses. Moreover, no previous studies have investigated exogenous carbohydrate oxidation rates during cross-country skiing. The current study investigated the effects of a 13C-enriched 18% multiple-transportable carbohydrate solution (1:0.8 maltodextrin:fructose) with additional gelling polysaccharides (CHO-HG) on substrate utilization and gastrointestinal symptoms during prolonged cross-country skiing exercise in the cold, and subsequent double-poling time-trial performance in ~ 20 °C. Methods Twelve elite cross-country ski athletes (6 females, 6 males) performed 120-min of submaximal roller-skiing (69.3 ± 2.9% of V̇ $$ \dot{\mathrm{V}} $$O2peak) in −5 °C while receiving either 2.2 g CHO-HG·min− 1 or a non-caloric placebo administered in a double-blind, randomized manner. Whole-body substrate utilization and exogenous carbohydrate oxidation was calculated for the last 60 min of the submaximal exercise. The maximal time-trial (2000 m for females, 2400 m for males) immediately followed the 120-min submaximal bout. Repeated-measures ANOVAs with univariate follow-ups were conducted, as well as independent and paired t-tests, and significance was set at P
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Purpose This study examined the effects of a novel maltodextrin-fructose hydrogel supplement (MF-H) on cycling performance and gastrointestinal distress symptoms. Methods Nine endurance-trained male cyclists (age = 26.1 ± 6.6, mass = 80.9 ± 10.4 kg, VO2max = 55.5 ± 3.6 mL·kg·min⁻¹) completed three experimental trials consisting of a 98-min varied-intensity cycling protocol followed by a performance test of ten consecutive sprint intervals. In a cross-over design, subjects consumed 250 mL of a treatment beverage every 15 min of cycling. Treatments consisted of 78 g·hr⁻¹ of either (a) MF-H, (b) isocaloric maltodextrin-fructose (ratio-matched 2:1; MF), and (c) isocaloric maltodextrin only (MD). Results There were no differences in average sprint power between treatments (MF-H, 284 ± 51 W; MF, 281 ± 46 W; and MD, 277 ± 48 W), or power output for any individual sprint. Subjective ratings of gastrointestinal distress symptoms (nausea, fullness, and abdominal cramping) increased significantly over time during the cycling trials, but few individuals exceeded moderate levels in any trial with no systematic differences in gastrointestinal discomfort symptoms observed between treatments. Conclusions In conclusion, ingestion of a maltodextrin/fructose hydrogel beverage during high-intensity cycling does not improve gastrointestinal comfort or performance compared to MF or MD beverages.
Purpose: To determine whether the pattern of carbohydrate sports drink ingestion during prolonged sub-maximal running affects exogenous carbohydrate oxidation rates and gastrointestinal (GI) comfort. Methods: Twelve well-trained male runners (27 ± 7 y, 67.9 ± 6.7 kg, V[Combining Dot Above]O2peak: 68 ± 7 mL·kg·min) completed two exercise trials of 100 min steady state running at 70% V[Combining Dot Above]O2peak. In each of the trials, 1 L of a 10% dextrose solution, enriched with [U-C] glucose, was consumed as either 200 mL every 20 min (CHO-20) or 50 mL every 5 min (CHO-5). Expired breath and venous blood samples were collected at rest and every 20 min during exercise. Subjective scales of GI comfort were recorded at regular intervals. Results: Average exogenous carbohydrate oxidation rates were 23% higher during exercise in CHO-20 (0.38 ± 0.11 vs. 0.31 ± 0.11 g·min; P=0.017). Peak exogenous carbohydrate oxidation was also higher in CHO-20 (0.68 ± 0.14 g·min vs. 0.61 ± 0.14 g·min; P=0.004). During exercise, total carbohydrate oxidation (CHO-20: 2.15 ± 0.47; CHO-5: 2.23 ± 0.45 g·min, P=0.412) and endogenous carbohydrate oxidation (CHO-20: 1.78 ± 0.45; CHO-5: 1.92 ± 0.40 g·min; P=0.148) were not different between trials. Average serum glucose (P=0.952) and insulin (P=0.373) concentrations were not different between trials. There were no differences in reported symptoms of GI comfort and stomach bloatedness (P>0.05), with only 3% of reported scores classed as severe (>5 out of 10). Conclusion: Ingestion of a larger volume of carbohydrate solution at less frequent intervals during prolonged submaximal running increased exogenous carbohydrate oxidation rates. Neither drinking pattern resulted in increased markers of GI discomfort to a severe level.
The timing of carbohydrate ingestion and how this influences net muscle glycogen utilization and fatigue has only been investigated in prolonged cycling. Past findings may not translate to running because each exercise mode is distinct both in the metabolic response to carbohydrate ingestion and in the practicalities of carbohydrate ingestion. To this end, a randomized, cross-over design was employed to contrast ingestion of the same sucrose dose either at frequent intervals (15 × 5 g every 5 min) or at a late bolus (1 × 75 g after 75 min) during prolonged treadmill running to exhaustion in six well-trained runners ( 61 ± 4 ml·kg ⁻¹ ·min ⁻¹ ). The muscle glycogen utilization rate was lower in every participant over the first 75 min of running (Δ 0.51 mmol·kg dm ⁻¹ ·min ⁻¹ ; 95% confidence interval [−0.02, 1.04] mmol·kg dm ⁻¹ ·min ⁻¹ ) and, subsequently, all were able to run for longer when carbohydrate had been ingested frequently from the start of exercise compared with when carbohydrate was ingested as a single bolus toward the end of exercise (105.6 ± 3.0 vs. 96.4 ± 5.0 min, respectively; Δ 9.3 min, 95% confidence interval [2.8, 15.8] min). A moderate positive correlation was apparent between the magnitude of glycogen sparing over the first 75 min and the improvement in running capacity ( r = .58), with no significant difference in muscle glycogen concentrations at the point of exhaustion. This study indicates that failure to ingest carbohydrates from the outset of prolonged running increases reliance on limited endogenous muscle glycogen stores—the ergolytic effects of which cannot be rectified by subsequent carbohydrate ingestion late in exercise.
Purpose: To examine the effect of altering osmolality or adding sodium alginate and pectin to a concentrated carbohydrate (CHO) beverage on gastric emptying (GE) rate. Methods: 500 mL boluses of three drinks were instilled double-blind in eight healthy males while seated and GE measured using the double sampling method for 90 min and blood samples collected regularly. Drinks consisted of glucose and fructose (MON, 1392 mOsmol/kg), maltodextrin and fructose (POLY, 727 mOsmol/kg) and maltodextrin, fructose, sodium alginate and pectin (ENCAP, 732 mOsmol/kg) with each providing 180 g/L CHO (CHO ratio of 1:0.7 maltodextrin/glucose:fructose). Results: Time to empty half of the ingested bolus was faster for ENCAP (21±9 min) than POLY (37±8 min), both were faster than MON (51±15 min). There were main effects for time and drink in addition to an interaction effect for the volume of test drink remaining in the stomach. There were no differences between MON or POLY at any timepoint. ENCAP had a smaller volume of the test drink in the stomach than MON at 30 min (193±62 vs 323±54 mL), which remained less up to 60 min (93±37 vs 210±88 mL). There was a smaller volume of the drink remaining in the stomach in ENCAP compared with POLY 20 min (242±73 vs 318±47 mL) and 30 min (193±62 vs 304±40 mL) after ingestion. Although there was a main effect of time, there was no effect of drink or an interaction effect on serum glucose, insulin or non-esterified fatty acid (NEFA) concentrations. Conclusion: The addition of sodium alginate and pectin to a CHO beverage enhances early GE rate but did not affect serum glucose, insulin or NEFA concentration at rest.
Purpose: Maximizing carbohydrate availability is important for many endurance events. Combining pectin and sodium alginate with ingested maltodextrin-fructose (MAL+FRU+PEC+ALG) has been suggested to enhance carbohydrate delivery via hydrogel formation but the influence on exogenous carbohydrate oxidation remains unknown. The primary aim of this study was to assess the effects of MAL+FRU+PEC+ALG on exogenous carbohydrate oxidation during exercise compared to a maltodextrin-fructose mixture (MAL+FRU). MAL+FRU has been well established to increase exogenous carbohydrate oxidation during cycling, compared to glucose-based carbohydrates (MAL+GLU). However, much evidence focuses on cycling, and direct evidence in running is lacking. Therefore, a secondary aim was to compare exogenous carbohydrate oxidation rates with MAL+FRU versus MAL+GLU during running. Methods: Nine trained runners completed two trials (MAL+FRU and MAL+FRU+PEC+ALG) in a double-blind, randomised crossover design. A subset (n=7) also completed a MAL+GLU trial to address the secondary aim, and a water trial to establish background expired CO2 enrichment. Participants ran at 60% V˙O2peak for 120 min while ingesting either water only, or carbohydrate solutions at a rate of 1.5 g carbohydrate·min. Results: At the end of 120 min of exercise, exogenous carbohydrate oxidation rates were 0.9 (SD 0.5) g·min with MAL+GLU ingestion. MAL+FRU ingestion increased exogenous carbohydrate oxidation rates to 1.1 (SD 0.3) g·min (p=0.038), with no further increase with MAL+FRU+PEC+ALG ingestion (1.1 (SD 0.3) g·min; p=1.0). No time x treatment interaction effects were observed for plasma glucose, lactate, insulin or non-esterified fatty acids, nor for ratings of perceived exertion or gastrointestinal symptoms (all p>0.05). Conclusion: To maximise exogenous carbohydrate oxidation during moderate-intensity running, athletes may benefit from consuming glucose(polymer)-fructose mixtures over glucose-based carbohydrates alone, but the addition of pectin and sodium alginate offers no further benefit.
Eight well-trained cyclists ingested 68 g·h ⁻¹ of a carbohydrate-electrolyte solution with sodium alginate and pectin (CHO-ALG) or a taste and carbohydrate type-matched carbohydrate-electrolyte solution (CHO) during 120 min of cycling at 55% maximal power followed by an ∼20 min time trial. Oxygen uptake, carbon dioxide production, blood glucose concentration, substrate oxidation, gastrointestinal symptoms, and time trial performance (CHO-ALG: 1219 ± 84 s, CHO: 1267 ± 102 s; P = 0.185) were not different between trials. Novelty Inclusion of sodium alginate and pectin in a carbohydrate drink does not influence blood glucose, substrate oxidation, gastrointestinal comfort, or performance in cyclists.
The impact of a carbohydrate-electrolyte solution with sodium alginate and pectin for hydrogel formation (CES-HGel), was compared to a standard CES with otherwise matched ingredients (CES-Std), for blood glucose, substrate oxidation, gastrointestinal symptoms (GIS; nausea, belching, bloating, pain, regurgitation, flatulence, urge to defecate, and diarrhea), and exercise performance. Nine trained male endurance runners completed 3 hr of steady-state running (SS) at 60% VO2 max, consuming 90 g/hr of carbohydrate from CES-HGel or CES-Std (53 g/hr maltodextrin, 37 g/hr fructose, 16% w/v solution) in a randomized crossover design, followed by an incremental time to exhaustion (TTE) test. Blood glucose and substrate oxidation were measured every 30 min during SS and oxidation throughout TTE. Breath hydrogen (H2) was measured every 30 min during exercise and every 15 min for 2 hr postexercise. GIS were recorded every 15 min throughout SS, immediately after and every 15-min post-TTE. No differences in blood glucose (incremental area under the curve [mean ± SD]: CES-HGel 1,100 ± 96 mmol·L −1 ·150 min −1 and CES-Std 1,076 ± 58 mmol·L −1 ·150 min −1 ; p = .266) were observed during SS. There were no differences in substrate oxidation during SS (carbohydrate: p = .650; fat: p = .765) or TTE (carbohydrate: p = .466; fat: p = .633) and no effect of trial on GIS incidence (100% in both trials) or severity (summative rating score: CES-HGel 29.1 ± 32.6 and CES-Std 34.8 ± 34.8; p = .262). Breath hydrogen was not different between trials (p = .347), nor was TTE performance (CES-HGel 722 ± 182 s and CES-Std: 756 ± 187 s; p = .08). In conclusion, sodium alginate and pectin added to a CES consumed during endurance running does not alter the blood glucose responses, carbohydrate malabsorption, substrate oxidation, GIS, or TTE beyond those of a CES with otherwise matched ingredients.