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Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans

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Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans

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Green tea consumption is reportedly associated with various health-promoting properties. For example, it has been shown to promote fat oxidation in humans at rest and to prevent obesity and improve insulin sensitivity in mice. We investigated the effects of acute ingestion of green tea extract (GTE) on glucose tolerance and fat oxidation during moderate-intensity exercise in humans. Two studies were performed, both with a counter-balanced crossover design. In study A, 12 healthy men performed a 30-min cycling exercise at 60% of maximal oxygen consumption (VO2max) before and after supplementation. In study B, 11 healthy men took an oral-glucose-tolerance test before and after supplementation. In the 24-h period before the experimental trials, participants ingested 3 capsules containing either GTE (total: 890 +/- 13 mg polyphenols and 366 +/- 5 mg EGCG) or a corn-flour placebo (total: 1729 +/- 22 mg). Average fat oxidation rates were 17% higher after ingestion of GTE than after ingestion of placebo (0.41 +/- 0.03 and 0.35 +/- 0.03 g/min, respectively; P < 0.05). Moreover, the contribution of fat oxidation to total energy expenditure was also significantly higher, by a similar percentage, after GTE supplementation. The insulin area under the curve decreased in both the GTE and placebo trials (3612 +/- 301 and 4280 +/- 309 microIU/dL . 120 min, respectively; P < 0.01), and there was a concomitant increase of 13% in insulin sensitivity. Acute GTE ingestion can increase fat oxidation during moderate-intensity exercise and can improve insulin sensitivity and glucose tolerance in healthy young men.
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Green tea extract ingestion, fat oxidation, and glucose tolerance in
healthy humans
1,2
Michelle C Venables, Carl J Hulston, Hannah R Cox, and Asker E Jeukendrup
ABSTRACT
Background: Green tea consumption is reportedly associated with
various health-promoting properties. For example, it has been shown
to promote fat oxidation in humans at rest and to prevent obesity and
improve insulin sensitivity in mice.
Objective: We investigated the effects of acute ingestion of green
tea extract (GTE) on glucose tolerance and fat oxidation during
moderate-intensity exercise in humans.
Design: Two studies were performed, both with a counter-balanced
crossover design. In study A, 12 healthy men performed a 30-min
cycling exercise at 60% of maximal oxygen consumption (V
˙
O
2
max)
before and after supplementation. In study B, 11 healthy men took an
oral-glucose-tolerance test before and after supplementation. In the
24-h period before the experimental trials, participants ingested 3
capsules containing either GTE (total: 890 13 mg polyphenols and
366 5 mg EGCG) or a corn-flour placebo (total: 1729 22 mg).
Results: Average fat oxidation rates were 17% higher after ingestion
of GTE than after ingestion of placebo (0.41 0.03 and 0.35 0.03
g/min, respectively; P 0.05). Moreover, the contribution of fat
oxidation to total energy expenditure was also significantly higher,
by a similar percentage, after GTE supplementation. The insulin area
under the curve decreased in both the GTE and placebo trials (3612
301 and 4280 309
IU/dL 120 min, respectively; P 0.01), and
there was a concomitant increase of 13% in insulin sensitivity.
Conclusions: Acute GTE ingestion can increase fat oxidation dur-
ing moderate-intensity exercise and can improve insulin sensitivity
and glucose tolerance in healthy young men. Am J Clin Nutr
2008;87:778 84.
KEY WORDS Tea catechins, substrate metabolism, oral-
glucose-tolerance test, moderate-intensity exercise, men
INTRODUCTION
The prevalence of obesity is reaching epidemic proportions in
many Western countries, with recently published data suggesting
that, in some states in the United States, the prevalence of obesity
is 30%. Because obesity and insulin resistance are major risk
factors for the development of type 2 diabetes mellitus and car-
diovascular disease, any potential treatment can have far-
reaching economic and medical implications.
Green tea contains a class of polyphenolic flavonoids known
as catechins, which comprise epigallocatechin gallate (EGCG),
epicatechin gallate, and gallocatechin gallate; EGCG is thought
to be the most pharmacologically active of the catechins. Several
experimental studies have indicated that chronic consumption of
green tea extract (GTE) can improve exercise performance,
increase fat oxidation, and prevent obesity in C57BL/6J mice
(1– 4). It has been suggested that GTE exerts these effects
through its action on the sympathetic nervous system, more
specifically on the breakdown of the catecholamine noradren-
aline. EGCG is a known inhibitor of the enzyme catechol
O-methyltransferase (5), which degrades noradrenaline, and
therefore EGCG can exert a regulatory effect on sympathetic
activation and lipolysis.
Although most studies with green tea have been performed in
animal models, Dulloo et al (6) showed that, in healthy young
men, a similar effect can be observed with acute GTE ingestion.
In their study, resting 24-h energy expenditure (EE) and the
contribution of fat oxidation to total EE were elevated.
During moderate-intensity exercise, EE is several times higher
than that during rest, and absolute rates of lipolysis and fat oxi-
dation also are higher (7, 8). To date, it remains unclear whether
EGCG can elevate fat oxidation and lipolysis during exercise
when fatty acid (FA) metabolism is already stimulated.
In addition to effects on fat metabolism, GTE may have an
effect on glucose tolerance and insulin sensitivity. When
Sprague-Dawley rats were fed a diet including 148 mg green tea
catechins/d for 12 d, fasting plasma glucose and insulin concen-
trations and the insulin response to an oral glucose load (2 g
glucose/kg body wt) were significantly reduced (9). In addition,
when spontaneously hypertensive rats, which are often used as a
genetic model of the metabolic syndrome, were fed a diet sup-
plemented with 200 mg EGCG kg
Ҁ1
d
Ҁ1
for 3 wk, insulin
sensitivity increased (10).
The first study presented in this report (study A) investigated
whether acute ingestion of GTE can increase fat oxidation rates
during moderate-intensity exercise. The second study (study B)
investigated the effects of acute ingestion of GTE on glucose
tolerance as assessed by a 2-h oral-glucose-tolerance test
(OGTT). We hypothesized that the acute intake of GTE will
increase fat oxidation during exercise and will improve glucose
tolerance in healthy young men.
1
From the Human Performance Laboratory, School of Sport and Exercise
Sciences, The University of Birmingham, Birmingham, United Kingdom.
2
Reprints not available. Address correspondence to AE Jeukendrup, School
of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Bir-
mingham, B15 2TT, United Kingdom. E-mail: a.e.jeukendrup@bham.ac.uk.
Received August 14, 2007.
Accepted for publication September 21, 2007.
778 Am J Clin Nutr 2008;87:778 84. Printed in USA. © 2008 American Society for Nutrition
by guest on June 12, 2013ajcn.nutrition.orgDownloaded from
SUBJECTS AND METHODS
Participants
Twelve male participants [x SD age: 26 2 y; weight: 75.1
3.2 kg; body mass index (BMI; in kg/m
2
); 23.9 0.8; maximal
oxygen consumption (V
˙
O
2
max): 50.9 2.1 mL kg
Ҁ1
min
Ҁ1
]
were recruited for study A. An additional 11 male participants
(age: 23 2 y; weight: 77.7 4.5 kg; BMI: 24.1 1.1; V
˙
O
2
max:
52.0 2.8 mL kg
Ҁ1
min
Ҁ1
) were recruited for study B. All
participants were healthy according to results of a general health
questionnaire.
All participants gave written informed consent to participate in
the study. Both study A and study B were approved by the Ethics
Subcommittee of the School of Sport and Exercise Sciences at
the University of Birmingham.
Preliminary testing
At least 1 wk before the first experimental trial, all participants
undertook an incremental exercise test, on an electronically
braked cycle ergometer (Lode Excalibur Sport, Groningen,
Netherlands), to volitional exhaustion. Participants started by
cycling at 95W for 3 min and increased their effort by incremental
steps of 35W every 3 min until they reached exhaustion. The
Wmax was calculated by using the following equation (11):
Wmax Wout [(t/180) 35] (1)
where Wout is the power output of the last completed stage, and
t is the time (in s) spent in the final stage. Wmax values were used
to determine the workload (50% Wmax) used in the later exper-
imental trials for study A. Respiratory gas measurements were
made by using the Douglas bag technique; oxygen consumption
(V
˙
O
2
) and carbon dioxide production were calculated by using
standard equations (12). Heart rate (HR) was measured contin-
uously by using telemetry and an HR monitor (Polar S625X;
Polar Electro Oy, Kempele, Finland). V
˙
O
2
was considered to be
maximal if 2 of the 3 following conditions were met: 1) a leveling
off of V
˙
O
2
with further increasing workloads (an increase of 2
mL kg
Ҁ1
min
Ҁ1
); 2) an HR within 10 beats/min of the age-
predicted maximum (220 bpm Ҁ age); and 3) a respiratory ex-
change ratio of 1.05.
General study designs
In a counter-balanced crossover design, each participant com-
pleted 2 trial days separated by 1 wk. In study A, each partic-
ipant completed 30 min of cycling exercise at 50% of their pre-
viously determined Wmax; in study B, each participant
underwent 2 OGTTs.
Diet and capsule content
In the 24-h period before the first trial, the participants were
asked to produce a food diary; this was replicated before the
second trial. During this 24-h period, participants ingested 3
capsules containing either GTE or a corn-flour placebo. The
capsules were ingested with lunch and dinner on the day before
the trial and in the morning, 1 h before the trial.
The GTE (Healthspan, St Peter Port, United Kingdom) con-
sisted of a standardized GTE (total of 340 mg polyphenols and
136 mg EGCG), maltodextrin, microcrystalline cellulose, so-
dium croscarmellose, stearic acid, silicon dioxide, magnesium
stearate (vegetable origin), hydroxypropylmethyl cellulose coat-
ing, and glycerine (vegetable origin). The capsule does not con-
tain caffeine. The amount of GTE contained in each capsule is
equivalent to 3.5 cups green tea. The placebo capsule contained
1517 48 mg of a gluten-free corn flour (Whitworths Ltd,
Wellingborough, United Kingdom).
Experimental protocol
Study A
All participants reported to the Human Performance Labora-
tory between 0700 and 0900 after a 10-h overnight fast and
having avoided strenuous exercise, alcohol, and caffeinated bev-
erages for the preceding 24 h. On their arrival, standard measures
of height and weight (Seca Alpha, Hamburg, Germany) were
taken. A flexible 20-gauge Teflon catheter (Venflon; Becton
Dickinson, Plymouth, United Kingdom) was then inserted into
an antecubital vein. A 3-way stopcock (PVB Medizintechnik,
Kirchseean, Germany) was attached to the catheter to allow re-
peated blood sampling during the test period. The participants
then mounted the cycle ergometer, and a resting blood sample (5
mL) was collected in EDTA-containing tubes (Becton Dickin-
son) and stored on ice for later centrifugation. Additional blood
samples, expiratory breath samples (2 min), and ratings of per-
ceived exertion were collected at 10-min intervals throughout the
exercise period. We kept the catheter patent by flushing it with
2–3 mL isotonic saline (0.9%; Baxter, Norfolk, United King-
dom) after each blood sample collection. HR was recorded con-
tinuously by telemetry with the use of a Polar S625X HR mon-
itor, and averages were taken of the final 5 min of each 10-min
interval.
Study B
All participants reported to the Human Performance Labora-
tory between 0700 and 0900 after a 10-h overnight fast and
having avoided strenuous exercise, alcohol, and caffeinated bev-
erages for the preceding 24 h. On their arrival, standard measures
of height and weight (Seca Alpha) were taken. A flexible 20-
gauge Teflon catheter (Venflon; Becton Dickinson) was then
inserted into an antecubital vein. A 3-way stopcock (PVB Mediz-
intechnik) was attached to the catheter to allow repeated blood
sampling during the test period. A resting blood sample (5 mL)
was taken, immediately after which the participants ingested a
25% glucose beverage consisting of 75 g glucose made up with
water to a volume of 300 mL (Meritose-200; Amylum UK Ltd,
London, United Kingdom). Further blood samples (5 mL) were
collected at 15, 30, 45, 60, 90, and 120 min while the participants
were seated. We kept the catheter patent by flushing it with 2–3
mL isotonic saline (0.9%; Baxter) after each blood sample col-
lection and at 75 and 105 min. Of the 5-mL blood sample, 3 mL
was collected into chilled EDTA-containing tubes (Becton Dick-
inson) and stored on ice; 2 mL was collected into serum tubes and
left to clot at room temperature.
Blood variables
All tubes were centrifuged at 1700 ҂ g for 10 min at 4 °C.
Aliquots of plasma and serum were immediately frozen in liquid
nitrogen and stored at Ҁ80 °C for later analysis. Where appro-
priate, plasma glucose (Glucose HK; ABX Diagnostics, Chick-
sands, United Kingdom), free FAs [(FFA) NEFA-C; Wako
Chemicals, Neuss, Germany], and glycerol (Raisio Diagnostics
GREEN TEA, FAT METABOLISM, AND GLYCEMIC CONTROL 779
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UK Ltd, Worksop, United Kingdom) were analyzed on a CO-
BAS MIRA semi-automatic analyzer (La Roche, Basel, Swit-
zerland). Serum insulin was analyzed by using an enzyme-linked
immunosorbent assay (DX EIA-2935 ELISA; IDS Ltd, Bolden,
United Kingdom).
Calculations
Study A
From the rate of carbon dioxide production and V
˙
O
2
(L/min),
total carbohydrate and fat oxidation rates (g/min) were calculated
by using the following stoichiometric equations of Jeukendrup
and Wallis (13), working under the assumption that protein ox-
idation during exercise is negligible:
Carbohydrate oxidation 4.210 V
˙
CO
2
2.962 V
˙
O
2
(2)
and
Fat oxidation 1.695 V
˙
O
2
1.701 V
˙
CO
2
(3)
Study B
From plasma glucose and serum insulin concentrations during
the 2-h OGTT, the whole-body insulin sensitivity index (ISI) was
calculated by using the following equation of Matsuda and De-
Fronzo (14):
ISI 1000/
(FPG FPI) (mean OGTT insulin concentration)
(mean OGTT glucose concentration)
(4)
where FPG is the fasting plasma glucose concentration, FPI is the
fasting serum insulin concentration, and 10 000 represents a con-
stant that allows numbers ranging between 1 and 12 to be ob-
tained. The square root conversion is used to correct the nonlinear
distribution of values.
Statistical analysis
Data analysis was performed by using SPSS for WINDOWS
software (version 12.0.1; SPSS Inc, Chicago, IL). Data are ex-
pressed as means SEs unless otherwise stated. Blood variables
over the course of the experimental trials were compared by
using a 2-factor (time ҂ trial) repeated-measures analysis of
variance. Paired-sample t tests compared the contribution of
substrate to total EE, the areas under the curve (AUCs) for glu-
cose and insulin, and the ISI in the different trials. Significance
was set at P 0.05.
RESULTS
Study A
Workload and exercise intensities
The workload of 50% Wmax (133 7W) used during the
30-min exercise trials elicited an average absolute V
˙
O
2
of 2300
99 and 2351 94 mL/min for the placebo and GTE trials,
respectively. Consequently, the average relative exercise inten-
sity (61 1% and 62 1% V
˙
O
2
max) and EE (11.35 0.48 and
11.57 0.45 kcal/min) between trials in the placebo and GTE
trials, respectively, did not differ significantly. In addition, there
were no significant differences in HR (134 4 and 136 4
bpm), rate of perceived exertion (12 1 and 12 1), or self-
selected cadence (85 2 and 87 3 rpm) between trials in the
placebo and GTE trials, respectively.
Carbohydrate and fat oxidation
The ingestion of GTE increased whole-body fat oxidation
significantly more than did that of the placebo trial (0.41 0.03
and 0.35 0.03 g/min, respectively; P 0.01 for main effect of
trial; Figure 1A). The relative contribution of substrates to total
EE can be seen in Figure 1B. Fat oxidation contributed 30% in the
FIGURE 1. Mean (SEM) fat oxidation measured every 10 min in the placebo (PLA) (F) and green tea extract (GTE) (E) trials (A) and contribution of
substrate (, fat; f, carbohydrate) to total energy expenditure over the course of the 30-min period in the PLA and GTE exercise trials (B). n ҃ 12. Differences
between trials were determined by using repeated-measures ANOVA (A) and a paired-sample t test (B).
*
P 0.05. Figure 1A indicates that there was a main
effect of the trial: ie, the GTE trial had significantly (P 0.01) higher fat oxidation rates than did the PLA trial.
780 VENABLES ET AL
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placebo trial and 35% in the GTE trial, which represents a sig-
nificant (P 0.05) increase of 17%. Correspondingly, the con-
tribution of carbohydrate was decreased by 17% after GTE in-
gestion (P 0.05).
Plasma metabolites and insulin
The effects of time and supplementation with or without GTE
on plasma glucose, insulin, FFAs, and glycerol can be seen in
Figure 2. Plasma glucose concentration was unaffected by GTE,
although there was a decrease with time in both trials (Figure 2A;
P 0.05). Plasma insulin concentrations displayed a similar
pattern, being unaffected by GTE but decreasing over time (Fig-
ure 2B; P 0.05). Plasma FFA concentrations after GTE inges-
tion were elevated, but th change was not significant (P ҃ 0.06
for main effect of trial; Figure 2C). GTE ingestion elicited sig-
nificantly higher plasma glycerol concentrations than did pla-
cebo ingestion (P 0.05 for main effect of trial; Figure 2D).
Study B
There were no significant differences in fasting plasma glu-
cose (5.04 0.08 and 5.12 0.08 mmol/L) or serum insulin
(8.16 1.53 and 7.93 1.40
IU/mL) concentrations between
trials in the placebo and GTE trials, respectively. However there
was a significant time effect on plasma glucose (P 0.01; Fig-
ure 3A) and also time and trial effects on serum insulin (P 0.01
for both), such that the GTE trial had lower serum insulin con-
centrations than the did placebo trial during the 2-h OGTT (Fig-
ure 3B).
The AUCs for plasma glucose (Figure 3C) did not differ be-
tween trials; however, the AUC for serum insulin was 15 4%
smaller during the GTE trial than during the placebo trial (3612
301 and 4280 309
IU/mL 120 min, respectively; P
0.01; Figure 3D). When the ISI of Matsuda and DeFronzo was
used, ISI was 13 4% greater during the GTE trial than during
the placebo trial (7.24 0.61 and 6.52 0.60, respectively; P
0.05; Figure 4).
DISCUSSION
The study reported here is the first to show that GTE can
increase fat oxidation during moderate-intensity cycling exercise
in healthy young men. It also observed that the acute ingestion of
GTE significantly reduced the insulin AUC during a 2-h OGTT
and improved insulin sensitivity. The study observed a 17%
FIGURE 2. Mean ( SEM) plasma concentrations of glucose (A), insulin (B), free fatty acids (FFA) (C), and glycerol (D) over the course of the 30-min
period in both the placebo (F) and green tea extract (E) exercise trials. n ҃ 12. Differences between trials were determined by using repeated-measures ANOVA.
Figure 2D indicates that there was a main effect of trial: ie, the plasma glycerol concentrations were significantly (P 0.05) higher in the green tea extract trial
than in the placebo trial.
GREEN TEA, FAT METABOLISM, AND GLYCEMIC CONTROL 781
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greater fat contribution to total EE during moderate-intensity
exercise when GTE was ingested than when placebo was in-
gested. This increase is in agreement with, yet not as great as, the
31% increase observed at rest by Dulloo et al (6). Several factors
may explain this difference; first, the GTE used in the study by
Dulloo et al contained 150 mg caffeine, a quantity that they
observed to be sufficient to increase EE and the fat contribution
to total EE by 7%. Second, evidence suggests that, during exer-
cise in the fasted state, caffeine can increase fat oxidation (15,
16). Third, the present study investigated the effect of GTE on fat
oxidation during exercise, rather than during rest, and it is known
that, during moderate-intensity exercise, both lipolysis and fat
oxidation already show marked increases compared with the
values during rest (8, 17–19). The present study therefore shows
that, even under conditions of elevated lipolysis and fat oxidation
seen during moderate-intensity exercise, GTE can increase fat
metabolism.
It is believed that GTE exerts its effects on fat oxidation
through the inhibition of catechol O-methyltransferase (5, 6), an
enzyme that degrades noradrenaline. This reduction in noradren-
aline degradation could potentially prolong adrenergic drive and
increase lipolysis. The higher plasma glycerol concentrations
seen during the GTE trial than during the placebo trial in the
present study have shown, albeit indirectly, that GTE can in-
crease lipolysis.
In addition to adrenergic drive, insulin is a well-known regu-
lator (ie, inhibitor) of lipolysis (20), and it could be conceived
FIGURE 3. Mean ( SEM) plasma glucose (A) and insulin (B) concentrations in the placebo (PLA) (E) and green tea extract (GTE) (E) trials and the area
under the curve (AUC) for glucose (C) and insulin (D) over the course of a 2-h oral-glucose-tolerance test in the 2 trials. n ҃ 11. Differences between trials were
determined by using repeated-measures ANOVA (A and B) and paired-sample t tests (C and D). P 0.01. Figure 3B indicates that there was a main effect
of trial: ie, the serum insulin concentrations were significantly (P 0.01) lower in the GTE trial than in the PLA trial.
FIGURE 4. Mean ( SEM) insulin sensitivity index in the placebo (PLA)
and green tea extract (GTE) trials. n ҃ 11. Differences between trials were
determined by using paired-sample t tests.
*
P 0.05.
782 VENABLES ET AL
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that, during the placebo trial, the corn flour may have elevated
plasma glucose, which resulted in insulin release and which
ultimately inhibited lipolysis. The difference between the 2 trials,
therefore, is due to a lower rate of lipolysis in the placebo trial,
rather than to a higher rate in the GTE trial. Thus, we rule out this
potential mechanism, because the amount of corn flour ingested
was minimal (1.5 g), and neither fasted glucose nor insulin con-
centrations differed significantly between trials.
Lipolysis during low-intensity exercise of this nature is not
thought to limit fat oxidation (21), and it could be that GTE has
additional effects on lipid metabolism. Chronic feeding of GTE
to mice has been shown to elevate the mRNA content of impor-
tant proteins involved in lipid transport and oxidation such as FA
translocase/CD36 and medium-chain acyl-CoA dehydrogenase
(1). In a similar study, GTE also reduced the content of malonyl
CoA (2), and, thus, it could relieve the inhibition on and increase
the activity of carnitine palmitoyl transferase
2
. Whether this can
occur with acute GTE feeding, either through a direct regulatory
action of GTE or due to the transient increase in FA, remains to
be seen. However, dietary manipulations that elevate plasma FA
can up-regulate many genes encoding for proteins involved in fat
metabolism (22). In addition, Watanabe et al (23) incubated
3T3-L1 adipocytes in a medium containing various concentra-
tions of EGCG for 15 min and observed an inhibition in the
enzyme acetyl CoA-carboxylase. EGCG could therefore alter the
partitioning of lipid in such a way that lipid is directed away from
storage and toward oxidation.
The present study also showed that GTE ingestion can increase
insulin sensitivity by 13% and, therefore, can reduce the insulin
response to a glucose load by 15%. Fructose-fed Sprague-
Dawley rats exhibit insulin resistance and hypertension, patho-
logic conditions that resemble type 2 diabetes mellitus in hu-
mans. When these rats were supplemented with GTE in addition
to fructose for 12 wk, they became more insulin sensitive. Fasting
plasma glucose and insulin concentrations were reduced to con-
trol concentrations, and plasma insulin concentrations during the
OGTT were significantly lower than those in the the rats fed
fructose only at all time-points. In parallel with this, increases in
adipocyte insulin–receptor binding and membrane GLUT 4 pro-
tein content were observed (9, 24). EGCG can also mimic insulin
by increasing the tyrosine phosphorylation of both the insulin
receptor and insulin receptor substrate-1 (25)—the first stage of
insulin-stimulated glucose uptake.
A further mechanism by which GTE could enhance glucose
tolerance may be the partitioning of lipid toward oxidation rather
than storage. The present study has shown an increase in fat
oxidation during moderate-intensity exercise, which could re-
duce the build-up of FA metabolites within the muscle. Such
metabolites are known to interfere with the insulin-signaling
cascade via the activation of novel isoforms of protein kinase C
(nPKC
and
) (26, 27). A reduction in the build-up of such
metabolites could therefore relieve the inhibition of the signaling
cascade and increase insulin-stimulated glucose uptake within
the skeletal muscle.
In conclusion, acute ingestion of green tea can increase fat
oxidation during moderate-intensity exercise, possibly through
an increase in lipolysis and therefore an increased availability of
fat as a fuel. Green tea ingestion can also improve glycemic
control after an oral glucose load and could have the potential to
reduce the risk of type 2 diabetes mellitus.
The authors’ responsibilities were as follows—MCV: study design, data
collection and analysis, and writing of the manuscript; CJH: data collection
and critical review of the manuscript; HRC: data collection; and AEJ: study
design and critical review of the manuscript. None of the authors had a
personal or financial conflict of interest.
REFERENCES
1. Murase T, Haramizu S, Shimotoyodome A, Nagasawa A, Tokimitsu I.
Green tea extract improves endurance capacity and increases muscle
lipid oxidation in mice. Am J Physiol Regul Integr Comp Physiol 2005;
288:R708 –15.
2. Murase T, Haramizu S, Shimotoyodome A, Tokimitsu I, Hase T. Green
tea extract improves running endurance in mice by stimulating lipid
utilization during exercise. Am J Physiol Regul Integr Comp Physiol
2006;290:R1550 6.
3. Murase T, Nagasawa A, Suzuki J, Hase T, Tokimitsu I. Beneficial effects
of tea catechins on diet-induced obesity: stimulation of lipid catabolism
in the liver. Int J Obes Relat Metab Disord 2002;26:145964.
4. Shimotoyodome A, Haramizu S, Inaba M, Murase T, Tokimitsu I. Ex-
ercise and green tea extract stimulate fat oxidation and prevent obesity in
mice. Med Sci Sports Exerc 2005;37:1884 –92.
5. Lu H, Meng X, Yang CS. Enzymology of methylation of tea catechins
and inhibition of catechol-O-methyltransferase by (-)-epigallocatechin
gallate. Drug Metab Dispos 2003;31:572–9.
6. Dulloo AG, Duret C, Rohrer D, et al. Efficacy of a green tea extract rich
in catechin polyphenols and caffeine in increasing 24-h energy expen-
diture and fat oxidation in humans. Am J Clin Nutr 1999;70:1040 –5.
7. Jeukendrup AE, Saris WH, Wagenmakers AJ. Fat metabolism during
exercise: a review—part II: regulation of metabolism and the effects of
training. Int J Sports Med 1998;19:293–302.
8. Romijn JA, Coyle EF, Sidossis LS, et al. Regulation of endogenous fat
and carbohydrate metabolism in relation to exercise intensity and dura-
tion. Am J Physiol 1993;265:E380 –91.
9. Wu LY, Juan CC, Ho LT, Hsu YP, Hwang LS. Effect of green tea
supplementation on insulin sensitivity in Sprague-Dawley rats. J Agric
Food Chem 2004;52:643–8.
10. Potenza MA, Marasciulo FL, Tarquinio M, et al. EGCG, a green tea
polyphenol, improves endothelial function and insulin sensitivity, re-
duces blood pressure, and protects against myocardial I/R injury in SHR.
Am J Physiol Endocrinol Metab 2007;292:E1378 87.
11. Kuipers H, Verstappen FT, Keizer HA, Geurten P, van Kranenburg G.
Variability of aerobic performance in the laboratory and its physiologic
correlates. Int J Sports Med 1985;6:197–201.
12. McArdle W, Katch F, Katch V. Exercise physiology: energy, nutrition
and human performance. Baltimore, MD: Lippincott Williams &
Wilkins, 2001.
13. Jeukendrup AE, Wallis GA. Measurement of substrate oxidation during
exercise by means of gas exchange measurements. Int J Sports Med
2005;26(suppl):S28 –37.
14. Matsuda M, DeFronzo RA. Insulin sensitivity indices obtained from oral
glucose tolerance testing: comparison with the euglycemic insulin
clamp. Diabetes Care 1999;22:1462–70.
15. Costill DL, Dalsky GP, Fink WJ. Effects of caffeine ingestion on me-
tabolism and exercise performance. Med Sci Sports 1978;10:155–8.
16. Ivy JL, Costill DL, Fink WJ, Lower RW. Influence of caffeine and
carbohydrate feedings on endurance performance. Med Sci Sports 1979;
11:6 –11.
17. Arner P, Kriegholm E, Engfeldt P, Bolinder J. Adrenergic regulation of
lipolysis in situ at rest and during exercise. J Clin Invest 1990;85:893– 8.
18. van Loon LJ, Greenhaff PL, Constantin-Teodosiu D, Saris WH,
Wagenmakers AJ. The effects of increasing exercise intensity on
muscle fuel utilisation in humans. J Physiol 2001;536:295–304.
19. Wolfe RR, Klein S, Carraro F, Weber JM. Role of triglyceride-fatty acid
cycle in controlling fat metabolism in humans during and after exercise.
Am J Physiol 1990;258:E382–9.
20. Campbell PJ, Carlson MG, Hill JO, Nurjhan N. Regulation of free fatty
acid metabolism by insulin in humans: role of lipolysis and reesterifi-
cation. Am J Physiol 1992;263:E1063–9.
21. Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Lipolytic sup-
pression following carbohydrate ingestion limits fat oxidation during
exercise. Am J Physiol 1997;273:E768 –75.
22. Cameron-Smith D, Burke LM, Angus DJ, et al. A short-term, high-fat
GREEN TEA, FAT METABOLISM, AND GLYCEMIC CONTROL 783
by guest on June 12, 2013ajcn.nutrition.orgDownloaded from
diet up-regulates lipid metabolism and gene expression in human skel-
etal muscle. Am J Clin Nutr 2003;77:313– 8.
23. Watanabe J, Kawabata J, Niki R. Isolation and identification of acetyl-
CoA carboxylase inhibitors from green tea (Camellia sinensis). Biosci
Biotechnol Biochem 1998;62:532–4.
24. Wu LY, Juan CC, Hwang LS, Hsu YP, Ho PH, Ho LT. Green tea supple-
mentation ameliorates insulin resistance and increases glucose transporter
IV content in a fructose-fed rat model. Eur J Nutr 2004;43:116 –24.
25. Waltner-Law ME, Wang XL, Law BK, Hall RK, Nawano M, Granner
DK. Epigallocatechin gallate, a constituent of green tea, represses he-
patic glucose production. J Biol Chem 2002;277:34933– 40.
26. Itani SI, Ruderman NB, Schmieder F, Boden G. Lipid-induced insulin
resistance in human muscle is associated with changes in diacylglycerol,
protein kinase C, and IkappaB-alpha. Diabetes 2002;51:2005–11.
27. Yu C, Chen Y, Cline GW, et al. Mechanism by which fatty acids inhibit
insulin activation of insulin receptor substrate-1 (IRS-1)-associated
phosphatidylinositol 3-kinase activity in muscle. J Biol Chem 2002;277:
50230 6.
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... In a crossover, double-blind study, Venables et al. [32] examined for the first time the effects of decaffeinated GTE (dGTE) intake on FO rates during exercise. Twelve healthy men completed a 30 min bout of moderate-intensity cycling exercise at 60% maximal oxygen consumption (VO 2max ) before and after a 24 h period of supplementation. ...
... Interestingly, average FO rates during cycling were 17% higher with GTE ingestion (0.41 ± 0.03 g/min) compared with placebo (0.35 ± 0.03 g/min). Furthermore, GTE supplementation resulted in a 17% higher contribution of FO to total EE [32]. More recently, Gahreman et al. [33] reported that acute GTE ingestion in untrained young females may increase FO rates after exercise. ...
... Overall, the findings regarding the metabolic effects of GT during exercise are contradictory. While some studies have shown that acute (24 h) or short-term (4 weeks) consumption of GT may increase FO during or after moderate-intensity exercise [32][33][34], other studies did not confirm these results [36][37][38][39][40][42][43][44]. ...
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Background Green tea (GT) consumption may influence fat oxidation (FO), body composition and blood lipid profile in human subjects. Therefore, this study aimed to review the current literature regarding the interactive effect of aerobic and resistance training with GT ingestion on these parameters. Methods Electronic searches were performed in Google Scholar, PubMed, Elsevier, Science Direct, and national databases. Only studies on human subjects that included GT intervention and aerobic or resistance exercise from any date to May 30, 2021 were reviewed. Results Twenty-seven papers (n = 831 participants) were included. From these, 12 studies addressed the acute or short-term effect of GT consumption on substrate oxidation during exercise, 2 studies assessed the long-term effect of GT consumption and aerobic exercise on substrate oxidation during exercise, 9 studies examined the short-term or long-term effects of GT intake and aerobic exercise on substrate oxidation or cardiometabolic risk factors, and 4 studies investigated the long-term effects of GT consumption and resistance training on substrate oxidation or cardiometabolic risk factors. Conclusions Short-term consumption of GT may have positive metabolic effects during moderate-intensity exercise in inactive people or those who exercise recreationally. Likewise, a combination of moderate-intensity aerobic training and GT consumption for a minimum period of 8 to 10 weeks can increase FO during exercise in healthy individuals. Regular resistance training combined with GT consumption may have potential benefits in enhancing body composition, lowering triglyceride, and increasing high-density lipoprotein in sedentary obese/overweight people.
... However, many studies with green tea extract (GTE) have shown an insulin-enhancing activity after an oral glucose tolerance test (OGTT) [14][15][16]; in several studies, it was also found that GTE has an effect on insulin sensitivity, fasting glucose, or glucose levels after OGTT [17][18][19]. ...
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Green tea powder (GTP) is rich in polyphenolic compounds, most particularly catechins. The effects of partial replacement of flour with GTP (10, 20, and 30%) on physicochemical properties, glycemic potential, and sensory attributes were investigated. Results showed a significant reduction in the moisture content, volume, and porosity of sample cakes with the increase in the GTP levels (P≤0.05). The utilization of GTP led to a harder texture and also darker color of sponge cake. The study showed that sponge cakes with good sensory attributes can be produced by the replacement of flour with 10% of GTP. Moreover, the glycemic potential and free radical scavenging activity of sample cakes improved as the GTP replacement increased (P≤0.05). GTP at 10% replacement level is recommended as it is very effective in improving the antioxidant properties, sensory attributes, and also glycemic potential.
... These results suggest new perspectives on the effects of green tea on body weight and highlight its potential benefits in the prevention or treatment of obesity and metabolic syndrome and its associated mechanisms [10] . With regard to the fact that human studies have focused on the effect of combining aerobic exercise and green tea supplementation on substance metabolism [11] , a decrease in lipid profile [12] and lipid oxidation [13] , and existing research in terms of the type of supplement, its dosage, and the type and length of exercise programs vary, and the results are inconsistent, there is little research on the effect of a period of aerobic exercise with green tea supplementation on the amount of weight-related variables such as glucose, triglycerides, etc. in obese men. So this paper aimed to investigate this issue and answer the question that whether consuming green tea with aerobic exercise can help reduce harmful variables such as LDL, etc. and improve the health index in positive variables such as HDL in obese men or not. ...
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Introduction and Purpose: The present study aimed to investigate the effect of 8 weeks of aerobic training with consuming green tea on the lipid profile and blood sugar of overweight men. Research Method: 40 overweight men (with the average height of 178± 5.61 cm, weight of 99 ± 8.03 kg, BMI of 30.79 ± 2.91 kg / m2) were selected from the Education General Office of Qazvin Province by simple random sampling method and randomly divided into four groups of ten control, consumption of green tea, aerobic exercise, and green tea consumption group with aerobic exercise individuals. Aerobic exercise was performed in three sessions per week, which was started from 65% to 85% in the last week and the consumption of green tea bags was in three servings per day, each serving included a two-gram pack of green tea in 200 ml of boiling water prescribed to the subjects of the respective groups during the eight-week experimental period of the study. To evaluate biochemical variables, bloodletting was performed after 14-12 hours of fasting in two stages, i.e., before training and after eight weeks of training as pre-test and post-test, respectively. Findings: After testing the research hypotheses by covariance analysis method, it can be said that eight weeks of aerobic training with green tea extract significantly reduced sugar levels (P = 0.024), triglycerides (003). P = 0), LDL (P = 0.039) of blood and significantly increased HDL (P = 0.021) of blood of the subjects. Conclusion: It can be argued that consuming the green tea supplementation along with aerobic training in overweight men reduces levels of sugar, triglycerides, and increases serum HDL.
... For instance, green tea extracts affect glycemic control by improving peripheral insulin sensitivity. In a study by Venables et al. [33], a 13% increase in the Matsuda measured insulin sensitivity was observed in response to acute ingestion of green tea extract in healthy males compared to the placebo. Although the exact mechanism for the observed effects of green tea is not yet known, it is hypothesised that green tea acts via glucose transporters in tissues such as skeletal muscle, thus requiring less insulin to clear a given amount of glucose [34]. ...
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Background: Piper excelsum (kawakawa) is an endemic shrub of Aotearoa, New Zealand, of cultural and medicinal importance to Māori. Its fruits and leaves are often consumed. These tissues contain several compounds that have been shown to be biologically active and which may underpin its putative health-promoting effects. The current study investigates whether kawakawa tea can modulate postprandial glucose metabolism. Methods: We report a pilot three-arm randomized crossover study to assess the bioavailability of kawakawa tea (BOKA-T) in six male participants with each arm having an acute intervention of kawakawa tea (4 g/250 mL water; 1 g/250 mL water; water) and a follow-up two-arm randomized crossover study to assess the impact of acute kawakawa tea ingestion on postprandial glucose metabolism in healthy human volunteers (TOAST) (4 g/250 mL water; and water; n = 30 (15 male and 15 female)). Participants consumed 250 mL of kawakawa tea or water control within each study prior to consuming a high-glycemic breakfast. Pre- and postprandial plasma glucose and insulin concentrations were measured, and the Matsuda index was calculated to measure insulin sensitivity. Results: In the BOKA-T study, lower plasma glucose (p < 0.01) and insulin (p < 0.01) concentrations at 60 min were observed after consumption of a high-dose kawakawa tea in comparison to low-dose or water. In the TOAST study, only plasma insulin (p = 0.01) was lower at 60 min in the high-dose kawakawa group compared to the control group. Both studies showed a trend towards higher insulin sensitivity in the high-dose kawakawa group compared to water only. Conclusions: Consuming kawakawa tea may modulate postprandial glucose metabolism. Further investigations with a longer-term intervention study are warranted.
... The energy requirements of moderate-intensity exercise are provided primarily by the oxidation of carbohydrates and lipids [1]. The relative contribution by the oxidation of carbohydrates and lipids towards the moderate-intensity exercise requirements are affected by dietary intake [2], training status [3], sex [4], exercise modality [5], environmental conditions [6], and supplementation (e.g., caffeine [7], green tea extract [8], Matcha green tea [9], New Zealand blackcurrant [10]). Many studies have examined the factors that contribute to exercise-induced maximal fat oxidation. ...
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New Zealand blackcurrant (NZBC) extract enhanced cycling-induced fat oxidation in female endurance athletes. We examined in recreationally active females the effects of NZBC extract on physiological and metabolic responses by moderate-intensity walking and the relationship of fat oxidation changes with focus on body composition parameters. Twelve females (age: 21 ± 2 y, BMI: 23.6 ± 3.1 kg·m−2) volunteered. Bioelectrical bioimpedance analysis was used for body composition measurements. Resting metabolic equivalent (1-MET) was 3.31 ± 0.66 mL·kg−1·min−1. Participants completed an incremental walking test with oxygen uptake measurements to individualize the treadmill walking speed at 5-MET. In a randomized, double-blind, cross-over design, the 30 min morning walks were in the same phase of each participant’s menstrual cycle. No changes by NZBC extract were observed for walking-induced heart rate, minute ventilation, oxygen uptake, and carbon dioxide production. NZBC extract enhanced fat oxidation (10 responders, range: 10–66%). There was a significant correlation for changes in fat oxidation with body mass index; body fat% in legs, arms, and trunk; and a trend with fat oxidation at rest but not with body mass and habitual anthocyanin intake. The NZBC extract responsiveness of walking-induced fat oxidation is body composition-dependent and higher in young-adult females with higher body fat% in legs, arms, and trunk.
Article
In women, fat oxidation during exercise changes with the menstrual cycle. This study aimed to investigate the effect of green tea extract (GTE) ingestion on fat oxidation during exercise depending on the menstrual cycle phase. Ten women with regular menstrual cycles participated in this randomized, double-blind, crossover study. GTE or placebo was administered during the menstrual cycle’s follicular phase (FP) and luteal phase (LP). Participants cycled for 30 min at 50% maximal workload, and a respiratory gas analysis was performed. Serum estradiol, progesterone, free fatty acid, plasma noradrenaline, blood glucose, and lactate concentrations were assessed before, during, and after the exercise. Fat oxidation, carbohydrate oxidation, and the respiratory exchange ratio (RER) were calculated using respiratory gas. Fat oxidation during the exercise was significantly higher in the FP than in the LP with the placebo (p < 0.05) but did not differ between the phases with GTE. Carbohydrate oxidation, serum-free fatty acid, plasma noradrenaline, blood glucose, and lactate concentrations were not significantly different between the phases in either trial. Our results suggest that GTE ingestion improves the decrease in fat oxidation in the LP.
Article
Introduction: Green tea is associated with a series of health benefits, as is physical training. However, in combination they present little known chronotropic and autonomic cardiac effects. Objective: To evaluate the effect of the association of chronic administration of green tea and physical training on basal heart rate (HR) and heart rate variability (HRV) in Wistar rats. Methods: Forty-three Wistar rats (Rattus norvegicus, var. albinus), paired by weight and age, were distributed among four experimental groups, titled sedentary control (CONsed, n = 10), trained control (CONtre, n = 08), sedentary tea (CHÁsed, n = 16) and trained tea (CHÁtre, n = 09). Ingestion of the tea was ad libitum. The physical training protocol lasted for eight weeks and consisted of sessions of swimming with incremental loads. At the end of the training, basal heart rate and heart rate variability (HRV) in both time and frequency domains were determined. The level of significance adopted was 5% (p < 0.05). Results: Both physical training and consumption of green tea caused higher resting bradycardia than that of the CONsed group animals. Regarding HRV, the CONtre, CHÁsed, and CHÁtre groups presented significantly higher values than the CONsed group. Supplementation with green tea caused an increase in the variance, high frequency (HF) component, and sympathovagal balance as compared to the CONsed group. Physical training (PT) did not enhance any of the parameters evaluated. Conclusions: There was no significant optimization of the hemodynamic or autonomic cardiovascular parameters resulting from the association between the administration of green tea and physical training in Wistar rats. Level of Evidence IV; Case Series.
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Objective Corydalis bungeana (CB) is a well-used medicinal herb in Mongolian folk medicine and has been traditionally applied as an antiobesity agent. However, the evidence-based pharmacological effects of CB and its specific metabolic alterations in the obese model are not entirely understood. This study aimed to utilize untargeted metabolomic techniques to identify biomarkers and gain mechanistic insight into the serum metabolite alterations associated with weight loss and lipid metabolism in obese rats. Methods A high-fat high-sugar (HFHS) diet was used to induce obese models in rats. CB extract was orally gavaged at 0.18, 0.9 and 1.8 g/kg doses for six weeks, and feed intake, body weight, fat pad weight, and blood indexes were measured. Blood serum metabolites were evaluated by gas chromatography/quadrupole time-of-flight tandem mass spectrometry (GC-TOF/MS). Results The results showed that compared with the obese group, the administration of CB extract caused significant decreases in body weight (P < 0.05), feed intake, Lee’s index, and perirenal, mesenteric, epididymal fat weight. CB extract also reduced blood triglyceride and total cholesterol levels (P < 0.05) of obese rats. Metabolomic findings showed that nine differential metabolites, including pyruvic acid, D-glucuronic acid, malic acid, dimethylglycine, oxoglutaric acid, pantothenic acid, sorbitol acid, fumaric acid and glucose 6-phosphate were identified under CB treatment and altered metabolic pathways such as TCA cycle, pantothenate and CoA biosynthesis, and glycolysis/gluconeogenesis. Conclusion This study demonstrated weight loss and lipid lowering effects of CB on HFHS diet-induced obese rats and identified nine metabolites as potential biomarkers for evaluating the favorable therapeutic mechanism of CB via regulation of lipid and glucose metabolism.
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In recent years, many efforts have been made to identify micronutrients or nutritional strategies capable of preventing, or at least, attenuating, exercise-induced muscle damage and oxidative stress, and improving athlete performance. The reason is that most exercises induce various changes in mitochondria and cellular cytosol that lead to the generation of reactive species and free radicals whose accumulation can be harmful to human health. Among them, supplementation with phenolic compounds seems to be a promising approach since their chemical structure, composed of catechol, pyrogallol, and methoxy groups, gives them remarkable health-promoting properties, such as the ability to suppress inflammatory processes, counteract oxidative damage, boost the immune system, and thus, reduce muscle soreness and accelerate recovery. Phenolic compounds have also already been shown to be effective in improving temporal performance and reducing psychological stress and fatigue. Therefore, the aim of this review is to summarize and discuss the current knowledge on the effects of dietary phenolics on physical performance and recovery in athletes and sports practitioners. Overall, the reports show that phenolics exert important benefits on exercise-induced muscle damage as well as play a biological/physiological role in improving physical performance.
Chapter
Consumption of functional foods may provide health benefits by reducing risk of many chronic diseases and improve structure and function of the human body. However, in the addition to the positive effect of absorption and digestion of functional ingredients, the interaction between food constituents and bioactives present in functional foods may strongly affect the bioavailability of dietary macronutrients and micronutrients. Gelation of dietary fiber in intestines may decrease digestibility and absorption of fat and carbohydrates but also may affect absorption of calcium, magnesium, and iron. In contrast, inulin and fructooligosaccharides may increase absorption of calcium and magnesium. High consumption of polyphenolic compounds, including tannins, can reduce bioavailability of iron and copper which may be a causative factor of anemia. Tannins present in green tea or its extracts may adversely affect functions. Thiocyanates, present cruciferous vegetables, may decrease iodine availability to the thyroid gland and decrease synthesis of precursors of thyroid hormones. This chapter will address positive and negative effects associated with absorption and digestibility of bioactive compounds.
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This study determined if the suppression of lipolysis after preexercise carbohydrate ingestion reduces fat oxidation during exercise. Six healthy, active men cycled 60 min at 44 ± 2% peak oxygen consumption, exactly 1 h after ingesting 0.8 g/kg of glucose (Glc) or fructose (Fru) or after an overnight fast (Fast). The mean plasma insulin concentration during the 50 min before exercise was different among Fast, Fru, and Glc (8 ± 1, 17 ± 1, and 38 ± 5 μU/ml, respectively; P< 0.05). After 25 min of exercise, whole body lipolysis was 6.9 ± 0.2, 4.3 ± 0.3, and 3.2 ± 0.5 μmol ⋅ kg-1⋅ min-1and fat oxidation was 6.1 ± 0.2, 4.2 ± 0.5, and 3.1 ± 0.3 μmol ⋅ kg-1⋅ min-1during Fast, Fru, and Glc, respectively (all P < 0.05). During Fast, fat oxidation was less than lipolysis ( P < 0.05), whereas fat oxidation approximately equaled lipolysis during Fru and Glc. In an additional trial, the same subjects ingested glucose (0.8 g/kg) 1 h before exercise and lipolysis was simultaneously increased by infusing Intralipid and heparin throughout the resting and exercise periods (Glc+Lipid). This elevation of lipolysis during Glc+Lipid increased fat oxidation 30% above Glc (4.0 ± 0.4 vs. 3.1 ± 0.3 μmol ⋅ kg-1⋅ min-1; P < 0.05), confirming that lipolysis limited fat oxidation. In summary, small elevations in plasma insulin before exercise suppressed lipolysis during exercise to the point at which it equaled and appeared to limit fat oxidation.
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• Contemporary stable isotope methodology was applied in combination with muscle biopsy sampling to accurately quantify substrate utilisation and study the regulation of muscle fuel selection during exercise. • Eight cyclists were studied at rest and during three consecutive 30 min stages of exercise at intensities of 40, 55 and 75 % maximal workload (Wmax). A continuous infusion of [U-13C]palmitate and [6,6-2H2]glucose was administered to determine plasma free fatty acid (FFA) oxidation and estimate plasma glucose oxidation, respectively. Biopsy samples were collected before and after each exercise stage. • Muscle glycogen and plasma glucose oxidation rates increased with every increment in exercise intensity. Whole-body fat oxidation increased to 32 ± 2 kJ min−1 at 55 % Wmax, but declined at 75 % Wmax (19 ± 2 kJ min−1). This decline involved a decrease in the oxidation rate of both plasma FFA and triacylglycerol fat sources (sum of intramuscular plus lipoprotein-derived triacylglycerol), and was accompanied by increases in muscle pyruvate dehydrogenase complex activation and acetylation of the carnitine pool, resulting in a decline in muscle free carnitine concentration. • We conclude that the most likely mechanism for the reduction in fat oxidation during high-intensity exercise is a downregulation of carnitine palmitoyltransferase I, either by this marked decline in free carnitine availability or by a decrease in intracellular pH.
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Nine trained cyclists were studied to determine the effects of caffeine (CAF), and glucose polymer (GP) feedings on work production (kpm) during two hr of isokinetic cycling exercise (80 rpm). Ingestion of 250 mg of CAF 60 min prior to the ride was followed by ingestion of an additional 250 mg fed at 15 min intervals over the first 90 min of the exercise. This treatment significantly increased work production by 7.4% and Vo2 by 7.3% as compared to control (C) while the subjects' perception of exertion remained unchanged. Ingestion of approximately 90 g of GP during the first 90 min (12.8 g/15 min) of the exercise had no effect on total work production or Vo2. It was, however, effective in reducing the rate of fatigue over the last 30 min of cycling. Although GP maintained blood glucose and insulin levels (P less than or equal to 0.05) above those of the C and CAF trials, total CHO utilization did not differ between treatments. During the last 70 min of the CAF trial, however, fat oxidation was elevated 31% and appeared to provide the substrate needed for the increased work production during this period of exercise. These data, therefore, demonstrate an enhanced rate of lipid catabolism and work production following the ingestion of caffeine.
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We have investigated the role of triglyceride-fatty acid cycling in amplifying control of the net flux of fatty acids in response to exercise and in recovery from exercise. Five normal volunteers were infused with [1-13C]palmitate and D-5-glycerol throughout rest, 4 h of treadmill exercise at 40% maximum O2 consumption, and 2 h of recovery. Total fat oxidation was quantified by indirect calorimetry. Lipolysis (rate of appearance of glycerol) increased from 2.1 +/- 0.3 to 6.0 +/- 1.2 mumol.kg-1.min-1 after 30 min of exercise and progressively increased thereafter to a value of 10.5 +/- 0.8 mumol.kg-1.min-1 after 4 h. Lipolysis decreased rapidly during the first 20 min of recovery, but it was still significantly elevated after 2 h of recovery. The rate of appearance of free fatty acids followed the same pattern of response. Seventy percent of released fatty acids were reesterified at rest, and this value decreased to 25% within the first 30 min of exercise. Reesterification remained less than 35% of lipolysis until the start of recovery, at which time the value rose to 90%. In exercise, more than one-half the increase in fat oxidation could be attributed to the reduction in the percent reesterification. Most of the change in percent reesterification during exercise and recovery was caused by changes in extracellular cycling of fatty acids released into plasma. We conclude that triglyceride-fatty acid cycling plays an important role in enabling a rapid response of fatty acid metabolism to major changes in energy metabolism.
Article
An aqueous methanol extract from green tea showed potent acetyl-CoA carboxylase inhibitory activity. An active compound was isolated from the extract and identified as (-)-epigallocatechin gallate by instrumental analyses, The IC50 value of (-)-epigallocatechin gallate was 3.1 x 10(-4) M. Among tea catechins and related compounds, nearly equal activity was found in(-)-epigallocatechin gallate and (-)epicatechin gallate, whereas (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, gallic acid and methyl gallate each had no inhibitory activity. These results indicate that the 3-O-gallate group of the catechin structure was necessary for this activity. (-)-Epigallocatechin gallate inhibited triglyceride accumulation in 3T3-L1 cells at a concentration of 1.0 x 10(-7) M or higher.
Article
In an effort to assess the effects of caffeine ingestion on metabolism and performance during prolonged exercise, nine competitive cyclists (two females and seven males) exercised until exhaustion on a bicycle ergometer at 80% of Vo2 max. One trial was performed an hour after ingesting decaffeinated coffee (Trial D), while a second trial (C) required that each subject consume coffee containing 330 mg of caffeine 60 min before the exercise. Following the ingestion of caffeine (Trial C), the subjects were able to perform an average of 90.2 (SE +/- 7.2) min of cycling as compared to an average of 75.5 (SE +/- 5.1) min in the D Trial. Measurements of plasma free fatty acids, glycerol and respiratory exchange ratios evidenced a greater rate of lipid metabolism during the caffeine trial as compared to the decaffeinated exercise treatment. Calculations of carbohydrate (CHO) metabolism from respiratory exchange data revealed that the subjects oxidized roughly 240 g of CHO in both trials. Fat oxidation, however, was significantly higher (P less than 0.05) during the C Trial (118 g or 1.31 g/min) than in the D Trial (57 g or 0.75 g/min). On the average the participants rated (Perceived Exertion Scale) their effort during the C Trial to be significantly (P less than 0.05) easier than the demands of the D treatment. Thus, the enhanced endurance performance observed in the C Trial was likely the combined effects of caffeine on lipolysis and its positive influence on nerve impulse transmission.
Article
The regulation of lipolysis, free fatty acid appearance into plasma (FFA R(a)), an FFA reesterification and oxidation were examined in seven healthy humans infused intravenously with insulin at rates of 4, 8, 25, and 400 mU.m-2.min-1. Glycerol and FFA R(a) were determined by isotope dilution methods, and FFA oxidation was calculated by indirect calorimetry or by measurement of expired 14CO2 from infused [1-14C]palmitate. These measurements were used to calculate total FFA reesterification, primary FFA reesterification occurring within the adipocyte, and secondary reesterification of circulating FFA molecules. Lipolysis, FFA R(a), and secondary FFA reesterification were exquisitely insulin sensitive [the insulin concentrations that produced half-maximal suppression (EC50), 106 +/- 26, 91 +/- 20 vs. 80 +/- 16 pM, P = not significant] in contrast to insulin suppression of FFA oxidation (EC50, 324 +/- 60, all P < 0.01). The absolute rate of primary FFA reesterification was not affected by the increase in insulin concentration, but the proportion of FFA molecules undergoing primary reesterification doubled over the physiological portion of the insulin dose-response curve (from 0.23 +/- 0.06 to 0.44 +/- 0.07, P < 0.05). This served to magnify insulin suppression of FFA R(a) twofold. In conclusion, insulin regulates FFA R(a) by inhibition of lipolysis while maintaining a constant rate of primary FFA reesterification.
Article
The adrenergic regulation of lipolysis was investigated in situ at rest and during standardized bicycle exercise in nonobese healthy subjects, using microdialysis of the extracellular space in subcutaneous adipose tissue. The glycerol concentration was about two times greater in adipose tissue than in venous blood. At rest, the glycerol concentration in adipose tissue was rapidly increased by 100% (P less than 0.01) after the addition of phentolamine to the ingoing perfusate, whereas addition of propranolol did not alter the adipose tissue glycerol level. Glycerol in adipose tissue and plasma increased during exercise and decreased in the postexercise period. Propranolol in the perfusate almost completely inhibited the increase in the tissue dialysate glycerol during the exercise-postexercise period. Phentolamine, however, was completely ineffective in this respect. During exercise, the lipolytic activity was significantly more marked in abdominal than in gluteal adipose tissue; this was much more apparent in women than in men. Thus, in vivo lipolysis in subcutaneous adipose tissue is regulated by different adrenergic mechanisms at rest and during exercise. Alpha-adrenergic inhibitory effects modulate lipolysis at rest, whereas beta-adrenergic stimulatory effects modulate lipolysis during exercise. In addition, regional differences in lipolysis are present in vivo during exercise, which seem governed by factors relating to sex.