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Journal of Exercise Physiologyonline
June 2015
Volume 18 Number 3
Editor-in-Chief
Official Research Journal of
Tommy
the American
Boone, PhD,
Society
MBA
of
Review
Board
Exercise
Physiologists
Todd Astorino, PhD
Julien Baker,
ISSN 1097-9751
PhD
Steve Brock, PhD
Lance Dalleck, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Yit Aun Lim, PhD
Lonnie Lowery, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Robert Robergs, PhD
Chantal Vella, PhD
Dale Wagner, PhD
Frank Wyatt, PhD
Ben Zhou, PhD
Official Research Journal
of the American Society of
Exercise Physiologists
ISSN 1097-9751
JEPonline
The Comparative Effects of Two Different Carbohydrate
Gels on Post-Exercise Glucose and Plasma Free-Fatty
Acids of Long Distance Runners
Beatriz G. Ribeiro1, Roberto Carlos-Burini2, Tiago C. Leite1, Anderson
P. Morales1,3, Felipe Sampaio-Jorge1,3, Gabriela M. O. Coelho1
1Laboratory
Research and Innovation in Sports Sciences, Federal
University of Rio de Janeiro/Macaé, RJ, Brazil, 2Department of Public
Health, Botucatu Medical School - University State São Paulo, São
Paulo, Brazil, ³Laboratory of Chemistry and Biomolecules, Higher
Institutes of Education of CENSA, Campos dos Goytacazes, RJ,
Brazil
ABSTRACT
Ribeiro BG, Carlos-Burini R, Leite TC, Morales AP, SampaioJorge F, Coelho GMO. The Comparative Effects of Two Different
Carbohydrate Gels on Post-Exercise Glucose and Plasma Free-Fatty
Acids of Long Distance Runners. JEPonline 2015;18(3):63-73. The
purpose of this study was to determine the post-exercise glucose and
free fatty acid (FFA) responses to two different carbohydrate gel
(CHO gel) supplementations. Body composition and dietary intake of
8 long distance runners were assessed prior to a 90-min run at 70%
VO2 max on a motorized treadmill. Blood samples were collected preand post-exercise when they received 1 g·CHO·kg–1 orally, either as
maltodextrin-glucose-fructose (MGF) or maltodextrin-glucose (MG) or
placebo (P). In both MGF and MG trials, blood glucose levels
increased similarly during the first 30 min of recovery in response to
the post-exercise ingested CHO supplement. In the P trial, blood
glucose levels remained unchanged during recovery. The area under
the curve was higher after the consumption of MG than MGF during
recovery. Plasma FFA levels decreased in both CHO supplement
trials and remained suppressed during recovery when compared to
the P trial (P<0.05). We conclude that supplement CHO gel MG trial
induced different patterns of plasma glucose postprandial time 60 and
90 min after exercise. Plasma FFA levels showed similar responses
after exercise, regardless of supplemental CHO (MG and MGF trials).
Furthermore, the decrease on plasma glucose levels occurred earlier
with MGF loading rather than MG alone.
Key Words: Carbohydrate Gel Supplementation, Athletes
64
INTRODUCTION
Post-exercise recovery represents an important challenge to modern athletes. Many athletes
undertake strenuous training programs involving one or more prolonged high-intensity exercise
sessions each day, typically with 6 to 24 hrs for recovery between sessions. This usually leads to
near depletion of body glycogen stores. Maximal glycogen storage is desirable for both athletic
competition and quality training. Muscle glycogen resynthesis after prolonged exercise has been well
investigated in relation to the amount, and timing of ingested carbohydrates (CHO) (5,21,24,30).
Ingestion of high CHO foods after exercise can increase liver and muscle glycogen storage. The
optimum restoration speed of muscular glycogen for athletes can be achieved when 1.0 to 1.85
g·CHO·kg-1·BW·hr-1 is offered right after exercise (4). However, the efficacy of a particular CHO in
promoting glycogen resynthesis depends on the CHO composition (6), and also on the plasma
glucose response to the CHO load (10).
Previous studies have shown that ingestion of a high glycemic index (GI) CHO is more effective in
promoting muscle glycogen resynthesis than the ingestion of a lower GI CHO (3,29). On the contrary,
Donaldson, Perry and Rose (9) reported in a review study that the GI is not as important as the
interaction between CHO and fat oxidation, which may play a role in increasing endurance exercise
performance.
Fructose seems to promote only a very modest increase in muscle glycogen, while the consumption
of fructose or sucrose provides a significant increase in liver glycogen storage during recovery period
(5,8). Little is known about the influence of co-ingestion of glucose and fructose supplementation
(e.g., pre-exercise, during exercise, and post-exercise) on the plasma residence time of glucose and
FFA post-exercise. The metabolic fate of fructose supplementation includes greater FFA blood
concentration, glucose, and glycogen synthesis (12). On the other hand, glucose supplementation
decreases post-exercise FFA concentration by the inhibition of lipolysis in adipocyte leading to a
lower rate of FFA oxidation (28).
The purpose of this study was to determine the post-exercise glucose and FFA responses to two
different CHO gels, maltodextrin-glucose-fructose or maltodextrin-glucose, during a 2-hr recovery
from 90 min of submaximal motorized treadmill running.
METHODS
Subjects
Eight long distance runners, volunteered to participate in this study. The mean age (30  4.7 yrs),
height, body mass, lean body mass, maximum oxygen uptake (VO 2 max) and maximum heart rate
(HR max) were determined (Table 1). All subjects were considered healthy, non-smokers. They were
not taking any medication, and did not have evidence of cardiovascular or metabolic diseases. The
experimental procedures and possible study risks were verbally explained. Afterwards, each subject
signed an informed consent form. The study protocol was approved by the ethics committee of the
Federal University of Rio de Janeiro.
65
Table 1. Subjects Characteristics.
Variables
Height (cm)
174  8.1
Weight (kg)
62.8  6.9
Body fat (%)
5.4  1.0
LBM (kg)
59.3  6.4
VO2 Max (mL·kg-1·min-1)
63.3  4.3
Heart Rate (beats·min-1)
183.8  9.3
Training Frequency (times·wk-1)
6.0  0.4
Training Duration (hrs·wk-1)
9.8  2.3
Values (Mean ± SD) for 8 subjects; LBM = Lean Body Mass; VO2 max = Maximal Oxygen Uptake
Pre-Experiment Measurements
Daily energy intake and dietary composition of habitual and 24-hr pre-test meals of long distance
runners were assessed using a 3-day food record. Dietary data (Table 2) were analyzed for energy
and macronutrient intake by the Evaluation System Nutritional Center for Health Informatics Paulista
School of Medicine, version 2.0, Brazil.
One week before the start of experimental trials, the subjects were familiarized with running on the
treadmill and experimental procedures. During the familiarization session, each subject was given
instructions for the use (i.e., proper running form) of the motorized treadmill (Inbrasport Master®). The
subjects undertook one preliminary test in order to determine VO 2 max using an uphill incremental
treadmill running test to exhaustion (17). Expired air samples were collected using the Cardio2
CPX/D Med Graphics Cardiopulmonary Exercise System and analyzed for VO2, carbon dioxide
(VCO2) production, and respiratory exchange ratio (RER). The VO 2 value obtained during the last min
of the VO2 max test was taken as the VO2 max value of the individual. One week before the first
experimental trial, the subjects undertook a 60-min treadmill run at 70% VO2 max in order to confirm
the relative exercise intensity and to fully familiarize themselves with prolonged treadmill running and
the measurements used during the experimental trials.
Testing Sessions
The subjects arrived at the laboratory at 7 a.m. on three occasions, each separated by 1 wk. They
were instructed to abstain from caffeine, alcohol, tobacco, and from heavy exercise 24 hrs prior to
each main trial. Daily energy intake and composition of each subject’s diet were assessed using a 24hr recall (Table 2). Before body mass (BM) was obtained, each subject was asked to empty his
bladder. Subsequently, a catheter (BD AngiocathTM, 18GAX1.88in, Bencton Dickinson, Brazil) was
inserted in an ante-cubital vein. A 10 mL resting venous blood sample was obtained.
66
In order to standardize the effect of dehydration on muscle metabolism during exercise, the subjects
consumed 4 mL·kg-1·BM-1 of cool water immediately before the warm-up and 2 mL·kg-1·BM-1 of water
every 20 min during the treadmill running test. The warm-up consisted of a 5-min run at an exercise
intensity equivalent to 60% of VO2 max, which was followed by a 90-min run at 70% of VO2 max. A
second venous blood sample was collected immediately after the run was completed. Then, the
subject’s dry post-exercise nude body mass was obtained. The subjects recovered for 2 hrs.
Immediately after the treadmill running test the subjects ingested a CHO gel that provided 1 g·kg-1·
BW·hr-1 of carbohydrate or placebo gel. The subjects ingested a CHO gel, over 2 min (t = −2 to 0
min), of either: (a) MGF: 35% maltodextrin, 50% glucose and 15% fructose; (b) MG: 50% maltodextrin
and 50% glucose: and (c) P: artificial sweetener. The artificially sweetened placebo mixture consisted
of sucralose® and was indistinguishable from the CHO-gel mixture. The CHO-gel was prepared
according to procedures described by Pierucci, Ribeiro, and Soares (25). The order of the
experiments was randomized and administered in a blind cross-over design. The subjects remained
in the laboratory and venous blood samples were taken every 30 min during a 2-hr resting recovery
period to determine glucose and FAA blood levels.
Blood Sample Collection and Analysis
Each venous blood sample was collected into an EDTA tube except for a 3 mL aliquot, which was
placed into a Sodium Flouride di-sodic EDTA for subsequent plasma glucose colorimetric
determination. Plasma was obtained by centrifugation at 2.500 rev·min-1 at 4ºC for 20 min. The
resultant plasma was stored at -20ºC until the analyses were performed. Plasma was analyzed for
glucose using a commercially available kit (GOD-POD-Kit Celm, Brazil), and for FFA with the
colorimetric method described by Novak (20). Blood (0.5 mL) was immediately analyzed for
hemoglobin concentrations (Kit Cellmlise II, CC-530 Celm, Brazil), and hematocrit using micro
capillary method. The hemoglobin and hematocrit values were used to calculate changes in plasma
volume (VP) (1). All analyses were made in duplicate.
Statistical Analyses
Descriptive statistics was used for all measured outcomes. The data are expressed as mean ± SD.
Differences between treatment groups were determined by two-way ANOVA of which one factor is
subject and the other is group. If a significant difference was indicated (P<0.05), the Tukey’s post hoc
test was used.
RESULTS
Dietary Assessment
The average total energy intake and dietary composition of 24 hrs before the trial was similar to the
daily habitual energy intake (Table 2). Total CHO intake was 9.9 ± 3.3 g·kg-1, 9.8 ± 3.7 g·kg-1, and
10.2 ± 3.5 g·kg-1 in the MGF, MG, and P trials, respectively. Dietary intake did not differ among the
trials.
67
Table 2. Dietary Composition of Habitual and 24 Hrs Pre-Test Meals of Long Distance Runners.
Nutritional Analysis
Dietary
24 Hrs
24 Hrs
24 Hrs
Component
Before
Before
Before
Habitual
MGF
MG
P
4234.0  1565
3984.2  1125
CHO (g)
633.3  209.9
624.0  193.8
615.2  237.9
641.0  222.7
CHO (%)
59.8  5.7
62.5  7.3
56.9  6.1
59.6  6.5
Protein (g)
154.7  48.2
157.2  50.1
186.3  108.4
175.5  54.2
Protein (%)
14.9  2.8
16.0  2.75
15.9  2.31
16.7  2.7
Fat (g)
125.2  73.1
100.7  41.5
141.1  81.2
119.6  65.4
Fat (%)
25.2  7.4
22.4  6.2
27.1  6.4
23.7  5.9
9.9  2.4
9.9  3.0
9.8  3.8
10.2  3.6
Energy (kcal)
CHO (g·kg·BM-1·d-1)
4458.4  2017
4345.8  1569
Values (Mean ± SD) for 8 Subjects. Maltodextrin-Glucose-Fructose (MGF), Maltodextrin-Glucose (MG), and Placebo (P);
CHO = Carbohydrates; BM = Body Mass
Fluid Ingestion, Volume Plasma Changes, and Body Mass
The mean water ingested was 848.7 ± 140.9 mL in the MGF trial, 926.2 ± 224.1 mL in the MG trial,
and 1000.0 ± 173.9 mL in the P trial during motorized treadmill. The consumption did not differ among
trials. Percentage changes in plasma volume were similar between the trials during motorized
treadmill (MGF: + 3 ± 4%; MG: +2 ± 4%; P: +5 ± 6%). Changes in body mass were similar among the
three trials during the treadmill running test (MGF: 1.8 ± 0.4 kg; MG: 1.7 ± 0.3 kg; P: 1.7 ± 0.5 kg).
Blood Glucose
In both the MGF and the MG trials, the subjects’ blood glucose levels increased during the first 30
min of the recovery period in response to the CHO gel ingested after the treadmill running test (Figure
1). In the P trial, the blood glucose levels remained unchanged during recovery period. In contrast, in
the MG trial, the blood glucose levels remained high until the 60 min of recovery period and was
higher (P<0.05) compared to P and at 90 min compared to MGF trial (Figure 1).
The area under the curve of plasma glucose levels was geometrically calculated by applying the
trapezoid rule to provide a measure of plasma glucose response to oral CHO gel load. The area
under the curve was higher after consumption of MG (87.12 mmol·L -1) than MGF (72.15 mmol·L-1)
during the recovery period.
68
Figure 1. Plasma Glucose Concentration Before (Pre) and After (Post) 90-Min Treadmill Run at 70% VO2
max and During Recovery After Ingestion or Not of 1 g·CHO·kg–1 Orally. Values are means  SE (error bars)
for 8 subjects. Maltodextrin-Glucose-Fructose (MGF), Maltodextrin-Glucose (MG), and Placebo (P). *Represents a
significant difference between P and MGF and MG trials (P<0.05). **Represents a significant difference between P and
MG trial (P<0.05). ***Represents a significant difference between MGF and MG trials (P<0.05).
Plasma FFA
Plasma FFA levels were higher after exercise compared to the resting values (P<0.05) (Figure 2).
FFA blood concentrations levels decreased in both CH gel trials (MGF and MG) and remained
suppressed until 90 min of recovery period when compared to P trial (P<0.05). Furthermore, the
blood FFA levels remained high in the P trial during recovery period.
Figure 2. Plasma FFA Concentration Before (Pre) and After (Post) 90-Min Treadmill Run at 70% VO2 Max
and During Recovery After Ingestion or Not of 1 g·CHO·kg–1 Orally. Means  SE (error bars). Values are
means  SD for 8 subjects. Maltodextrin-Glucose-Fructose (MGF), Maltodextrin-Glucose (MG), and Placebo (P).
*Represents a significant difference between P in post exercise time point and are both trials (MGF and MG), P<0.05.
69
DISCUSSION
Accepted standards on carbohydrate ingestion studies that promote glucose and FFA responses
have always been performed with intravenous infusions of glucose and fructose or with oral ingestion
of glucose polymers, sucrose, glucose or fructose isolated taken in liquid or solid states (5,24,30).
This study focused on the effects of oral CHO gel supplement intake on plasma glucose and FFA
during a 2-hr recovery period. The CHO gel consisted of maltodextrin - glucose with or without
fructose because athletes use these supplements regularly, especially when the sport includes
aerobic resistance training.
The main finding in this study is that different CHO gel induced different postprandial plasma glucose
patterns. The maltodextrin-glucose-fructose (MGF) gel resulted in a smaller area of the glucose curve
after 60 and 90 min of recovery from exercise compared to the maltodextrin-glucose (MG) gel. The
results also showed that the MG gel stimulated a higher glycemic response than the MGF gel without
changing the plasma FFA concentrations. Some studies have demonstrated that energy supplements
containing fructose and sucrose resulted in lower glycemic response when compared to those
containing either glucose or its polymers (5,24,30).
Elevation of glucose levels, as well as its duration depends on carbohydrate absorption speed
especially glucose absorption speed, which varies according to several factors such as gastric
emptying, hydrolysis speed, and the diffusion of hydrolyzed products in the small intestine (4). It
is well known that fructose by itself has a low rate of intestinal absorption, but the mixture of
glucose and fructose is well absorbed through additional transport mechanisms (32). This mechanism
is explained by the different membrane transport, as facilitated passive transport independent of
sodium via GLUT5 for fructose and facilitated diffusion via SGLT1 for glucose (33). It is believed that
glucose and fructose are not competing for the same carrier, indicating a better efficiency in
absorption and oxidation (13). Currell and Jeukendrup (7) confirmed that a mixture of glucose and
fructose (1.2 and 0.6 g·min-1, respectively), resulted in significantly better cycling performance in a
time-trial compared with a beverage containing only glucose.
In the present study, the addition of fructose to glucose and maltodextrin in CHO gel did not reduce
the 30-min postprandial glucose response (Figure 1). On the other hand, the lower AUC for the MGF
could be explained by the difference in CHO composition of the gels. The fructose metabolism is
predominantly hepatic with slight impact of insulin levels and/or glucose plasma levels in healthy
subjects (16). Petersen and colleagues (22) detected that fructose infusion tripled hepatic glycogen
synthesis in healthy subjects during the euglycemic hyper insulin clamp.
The mechanism is not fully understood but it is known that fructose-1-phosphate (a metabolite formed
in the liver by fructokinase that phosphorylates quickly fructose, using a molecule of ATP), has the
ability to dissociate glucokinase from glucokinase regulatory protein (GKRP). The glucokinase
dissociation from GKRP allows the glucokinase translocation from nucleus to the cytosol where it can
phosphorylate glucose, thus increasing liver glycogen resynthesis (19). This result is well established
through negative correlation in a high level of intracellular glucose-6-phosphate (via glucose
substrate) and a low concentration of ATPs (via substrate fructose) G6-P/ATP with the activation
state of enzyme glycogen synthase (GS) in hepatocytes from normal and diabetic animals incubated
with a mixture of 20 mM glucose and 3 mM fructose (6). This is a likely explanation for the decreased
blood glucose found in MGF compared to MG (Figure 1), within 90 min of recovery.
70
However, Casey et al. (5) found that the consumption of 1 g·kg-1 of weight of glucose post-exercise
promoted higher increase of plasma glucose than equal amounts of sucrose. Besides glycemia
differences, storage of glycogen found in the liver and the muscle were similar to both groups.
Differences in CHO administration route (oral x parenteral) and in techniques of liver glycogen
evaluation could explain the diversity of results found in different studies. Casey et al. (5) pointed out
that, 1 g·kg-1 BM glucose or sucrose is sufficient to start post-exercise liver glycogen resynthesis.
Therefore, the intake of energy supplements containing fructose between intense workouts would
provide energy substrates for liver glycogen restoring and physical exercise continuation.
The behavior of plasma glucose and FFA varies after exercise based upon the intensity and duration
of the physical effort. In accordance with previous studies (2,14,15) the present study (after the 90min run at 70% of VO2 max) showed a significant increase of FFA levels in the placebo group, which
was maintained for up to 2 hrs after exercise (Figure 2). Borsheim, Knardahl, and Hostmark (2)
demonstrated that the plasma concentration of non-esterified fatty acids remained significantly
elevated and constant even 3 hrs after the end of a long duration exercise. The effect is attributed to
adrenergic stimulation of hormone-sensitive adipocyte lipase.
The lack of this plasma FFA response was seen, in both groups supplemented with carbohydrates,
at plasma glucose of 30 min (Figures 1 and 2). This response was probably due to reduced lypolysis,
re-esterification of FFA into TG, increase or an elevation in the oxidative tissue uptake or a
combination of the three possibilities.
The reduced lipolysis was a consequence of higher plasma insulin triggered by higher plasma
glucose levels. Insulin diminishes cyclic AMP concentrations in adipocyte; consequently, blocking
the hormone sensitive lipase stimuli (18,27). Under these conditions, a high level of insulin and a
lower concentration of urinary catecholamines were found in 20 men supplemented with a mixture of
50 g glucose and 15 g fructose in the recovery period after aerobic exercise on a bicycle ergometer
(11). It is believed that such addition of supplemental fructose results in less sensitivity to high levels
of blood insulin. It has been suggested that an overload formation of lipid metabolites (Glycerol-3Phosphate - precursor in the synthesis of triacylglycerol) derived from fructose, could interfere with
the insulin signaling (31), accompanied by an inflammatory response mediated gene activated NF-κB
(nuclear factor κB) and involvement of inflammatory cytokines, such as muscle TNF-α (tumor
necrosis factor-α) (26).
CONCLUSIONS
In conclusion, this study showed that both trials with supplementation after exercise are effective in
increasing plasma glucose during recovery. However, the presence of fructose attenuated plasma
glucose levels after 60 and 90 min of recovery without changes in plasma FFA levels. Therefore, to
restore the glycogen as soon as possible, we recommend not eating fructose during the early
recovery period because attenuated plasma glucose levels will decrease the rate of glycogen
synthesis.
71
ACKNOWLEDGMENTS
The authors would like to thank the IMMT/Macaé, FESPORTUR/Macaé and FAPERJ.
Address for correspondence: Beatriz G. Ribeiro, PhD, Laboratory Research and Innovation in
Sports Sciences, Federal University of Rio de Janeiro - Macaé Campus, RJ, Brazil. 159, Alcides da
Conceição, Granja dos Cavaleiros, Macaé, Rio de Janeiro, Brazil 27930-560. +552227933-378;
[email protected]
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