1Department of Applied Nutrition, The University
of Tokushima School of Medicine, Tokushima, Japan;2School
of Social Health, Fukuoka Prefecture University, Fukuoka,
Japan;3Suntory Research Center, Osaka, Japan;and
4School of Food and Nutrition, Seinan Junior
College, Fukuoka, Japan
Abstract:Oolong tea is a traditional Chinese tea that has
long been believed to be beneficial to health such as decreasing
body fat. We were interested in this assertion and tried
to evaluate the effect of oolong tea on energy expenditure
(EE) in comparison with green tea. The subjects were eleven
healthy Japanese females (age 20±1 y; body mass
index (BMI) 21.2±2.5kg/m2)who each consumed of
three treatments in a crossover design:1) water, 2) oolong
tea, 3) green tea. Resting energy expenditure (REE) and
EE after the consumption of the test beverage for 120 min
were measured using an indirect calorimeter. The cumulative
increases of EE for 120 min were significantly increased
10% and 4% after the consumption of oolong tea and green
tea, respectively. EE at 60 and 90 min were significantly
higher after the consumption of oolong tea than that of
water (P<0.05). In comparison with green tea, oolong
tea contained approximately half the caffeine and epigallocatechin
galate, while polymerized polyphenols were double. These
results suggest that oolong tea increases EE by its polymerized
polyphenols.
J. Med. Invest. 50:170-175, 2003
Keywords:oolong tea, green tea, energy expenditure, women,
catechin, polyphenols
INTRODUCTION
Oolong tea is a traditional Chinese tea that is also popular
in Japan. In China, oolong tea has long been believed to
be beneficial to health (1). A recent study with 102 Chinese
females showed that continuous consumption of oolong tea
for 6 wk led to body weight reduction (2). Food related
weight reduction is mainly by two mechanisms:one is the
increase in energy expenditure (EE) and the other is the
inhibition of nutrient absorption. Major components of oolong
tea are polyphenols, caffeine and amino acids (3). There
are many studies that show the increase of EE by caffeine
in rodents (4, 5) and humans (6-14). Whether the increase
in EE that accompanies the consumption of oolong tea is
due solely to caffeine or other constituents such as polyphenolic
compounds is controversial (15, 16).
Green tea and oolong tea are produced from a single plant
species, but are distinguished by the processing technique.
For the production of green tea, the leaves are steamed
soon after the harvest to stop the enzyme reactions and
then ground by hand to break the cells of the leaves. On
the other hand for the production of oolong tea, the leaves
are kept under certain conditions to produce specific flavors
by enzyme reactions (fermentation). The specific flavors
of the fermented tea are due to the polymerized polyphenols.
The leaves of oolong tea are not ground and the leaf cells
are not broken. By these differences in the processing,
the components of green tea and oolong tea are different.
In Japan, powdered green tea is also popular and used for
tea ceremonies. The present was designed to assess whether
the consumption of oolong tea increase EE in comparison
with green tea.
SUBJECTS AND METHODS
Study design
The treatments were 1) water, 2) oolong tea and 3) green
tea. All subjects took water treatment on the first day.
Then they were randomly divided into two groups, and assigned
to oolong tea or green tea treatment in a crossover design.
Subjects
Eleven healthy young women were recruited from the student
population majoring in nutrition at a university. Medical
and nutritional histories were obtained by use of a questionnaire.
Smokers and those who engaged in intense physical activities
or had a history of weight loss were not included in the
current study. At the onset of the study, body weight and
height were measured. Mean (± SD) values for
some of the physical characteristics of the subjets were
as follows:age, 20±1y;height 163.4±0.9
cm (160.5-168.1);weight, 56.3±2.3 kg (47.2-68.6);and
body mass index (BMI) 21.1±0.8kg/m2 (18.2-25.9).
With the consideration of physiological differences in menstrual
cycle, we carried out the study when the subjects were in
the follicular phase. The subjects gave their written informed
consent to participate in the study. The University of Tokushima
Committee for Studies involving Human Subjects, approved
all procedures.
Experimental design
Subjects consumed a standardized meal (600 kcal, 28 g protein,
15 g lipids) between 19:00-20:00 on the day preceding each
session. They were allowed to take only water after the
meal. They stayed at the metabolic ward. The time schedule
at the metabolic ward was as follows:bed at 23:00 on the
previous night, rising at 6:00, toilet, rest in a reclining
chair for 30 min, collection of expired gas for 5 min to
measure resting energy expenditure (REE), consumption of
the test beverage in 5 min, collection of expired gas for
5 min followed by the consumption every 30 min for 120 min
to measure EE in the resting condition. For the measurement
of EE, expired gas was collected in a Douglas bag, the volume
was measured with a gas meter, and carbon dioxide and oxygen
contents were analyzed with a gas monitor (RE 3000, Fukuda
Denshi Co., Tokyo, Japan).
Oolong tea was obtained from Suntory Ltd (Osaka, Japan)
prepared in bags containing 15 g of tea leaves per bag.
The tea was brewed by adding 300 ml of boiling distilled
water to a glass container containing the tea bag. The tea
was steeped for 5 min, and the bag was then removed. Green
tea was obtained from Suntory Ltd (Osaka, Japan) prepared
with 5 g of powdered green tea, and dissolved in 300 ml
of boiling distilled water. Tea for all subjects was prepared
each morning and cooled to 37°C before drinking.
The strength of teas used in this study was well accepted
by the subjects.
Analyses of caffeine, flavanols and other polyphenols
Concentration of caffeine, flavanols and other polyphenols
(fractions including polymerized flavanols and other flavonoids)
in the oolong tea and the green tea were analyzed by HPLC
with UV detection at 280 nm (17). Analysis was performed
with a Cosmosil 5PE-MS column (4.6 mm i.d.×150
mm;Nakarai Tesque, Kyoto, Japan) at 40°C. Compounds
were eluted (eluent A:0.05% trifluoroacetic acid in water;eluent
B:0.05% trifluoroacetic acid in acetonitrile) at a flow
rate of 2 mL/min using a gradient program (eluent B content:10%
for 5 min, from 10% to 21% in 8 min, from 21% to 90% in
1 min and 90% for 6 min). The quantification of caffeine,
flavanols and other polyphenols was determined using standard
calibration curves for known compounds purchased commercially:caffeine
was from Nakarai Tesque Inc. (Kyoto, Japan). Epigallocatechin
(EGC), catechin (C), epicatechin, epigallocatechin gallate
(EGCG), gallocatechin gallate (GCG), epicatechin gallate
(ECG) and catechin gallate (CG) were from Kurita Water Industries
LTD (Tokyo, Japan). Other polyphenols were quantified using
a calibration curve that was derived from polyphenols, which
had been isolated from tea by HPLC.
Table 1 shows all analyzed components including caffeine,
individual catechins and other polyphenols. The lower-case
concentrations of caffeine and EGCG were approximately half
in the oolong tea (77 mg/300 ml and 81 mg/300 ml, respectively)
compared with those in the green tea (161 mg/300 ml and156
mg/300 ml, respectively), while the concentration of polymerized
polyphenols was much higher in the oolong tea (68 mg/300
ml) than that in the green tea (17 mg/300 ml). For the concentrations
of the other polyphenols, there was no marked difference
between the oolong tea and the green tea.
Statistics
All values were expressed as means±SE and analyzed
using a procedure from SAS/ATAT software, version 8, of
the SAS system for personal computers (SAS Institute, Cary,
NC). Since we had a small number of subjects, statistical
comparisons were made by ANOVA. Significant differences
in EE and RQ among treatments were determined by the Tukey-Kramer
test and repeated measurements in each treatment were determined
using the paired t test with the comparison to the REE level.
Differences were considered to be significant at P<0.05.
RESULTS
Fig. 1 shows the REE and EE measured for 120
min following the consumption of water, green tea or oolong
tea. REE were similar among the 3 treatments (206.6±3.7,
207.8±4.1 and 211.2±3.7 kJ/h for oolong
tea, green tea and water treatment, respectively). While
EE after the consumption of water was constant around the
REE level for 120 min, EE after the consumption of oolong
tea or green tea were increased immediately (EE at 30 min:P<0.01)
and gradually up to 90 min, then maintained until 120 min.
The maximum value of EE after the consumption of oolong
tea and green tea were at 90 min:237.3±10.1 and
223.2±3.9 kJ/hr, respectively. The values of
EE at 60 and 90 min after the consumption of oolong tea
were significantly higher than those after the consumption
of water (P<0.05). The cumulative increases of EE after
the consumption of oolong tea, green tea or water above
REE was 110.7±17.7, 49.5±0.4 and 11.2±1.1
kJ/2h, respectively.
Fig. 2 shows the variations of non-protein respiratory quotients
(RQ). RQ at the measurement of REE was not significantly
different among the treatments (0.82±0.01, 0.81±0.01
and 0.82±0.01 for oolong tea, green tea and water
treatment, respectively) and stayed constant until the end
of the measurement in 3 treatments.
INFLUENZA-ENCEPHALITIS AND REYE'S SYNDROME
Reye's syndrome is characterized by encephalitis and fatty
degeneration of the liver due to an impaired free fatty
acid metabolism and β-oxidation in mitochondria in
children treated with aspirin, ibuprofen and diclofenac,
and, in over 85% of cases, infected with influenza or varicella
(15, 16). To determine whether a disorder of mitochondrial
β-oxidation is a risk factor for influenza encephalopathy
or encephalitis, we infected newborn JVS mice and acquired
carnitine deficiency mice with non-neurotropic IAV/Aichi/2/68
(H3N2), which has been classified as a dominant and epidemic
influenza subtype since 1968. Carnitine is an obligatory
amino acid for the transfer of long-chain fatty acids from
the cytosol to mitochondria. These fatty acids contribute
the major source of energy in the mitochondria, particularly
in patients with high fever, vomiting and anorexia during
the newborn/suckling periods. Antipyretics, such as aspirin,
ibuprofen and diclofenac, have potent anti-inflammatory
effects, though impair the mitochondrial fatty acid metabolism
and generation of ATP. Furthermore, influenza virus proteins,
such as M protein, PB2 and PB1-F2, also cause mitochondrial
damage and inhibition of β-oxidation (17, 18). Therefore
influenza virus infection in combination with antipyretic
treatment may cause a systemic disorder of fatty acid metabolism,
particularly in the newborn/suckling period (19). Newborn
JVS mice have significantly higher numbers of virus-genome
in the brains, accumulation of virus antigen in the capillaries,
and an increased blood-brain barrier permeability after
intranasal infection with non-neurotropic IAV. Mini-plasmin
was prominently accumulated with virus antigen in the brain
capillaries of JVS mice, but only mildly in WT mice. Although
the mechanisms of IAV-associated encephalopathy by antipyretics
have not been clarified, Funato et al. have recently described
a single-base mutation of the CYP2C9 gene, the major cytochrome
P450 gene product that catalyzes diclofenac in human liver,
in one of thirty healthy subjects (20). This mutation in
the CYP2C9 gene may be related to diclofenac-induced influenza-virus-associated
encephalitis or encephalopathy.
DISCUSSION
The major components of oolong tea and green tea were caffeine
and polyphenols (Table 1). Caffeine is well known to increase
EE (4-14). Recently, Rumpler et al. (16) compared 24-h EE
of those who consuming oolong tea with that of those who
consumed water containing 270 mg caffeine, which was equivalent
to the concentration in the tea, and observed that while
EE was increased 2.9% for the oolong tea, it was increased
3.4% for the caffeinated water. From this result, they suggested
that the caffeine was the main factor in causing the increase
of EE. In contrast, Dulloo et al. (15) reported that the
consumption of water containing 150 mg caffeine did not
affect the 24-h EE, while the consumption of green tea extract
which contained equivalent amounts of caffeine elevated
24-h EE 4% above the water alone. From the result they suggested
that EGCG, which constituted about 70% of total catechins,
was the major factor in causing the increase of EE.
In the current study, the subjects consumed the test beverages
without a meal and measured the EE for 2 h. Since the metabolism
of caffeine and polyphenols are swift, the plasma caffeine
peaks at 1 h (18) and plasma polyphenols peaks at 3 h (19),
the effect of these tea components on EE can be observed
more clearly when the test beverage is administratered alone
and the EE can be determined at the expected time when the
tea components reached their peak level. If might be better
to measure the EE after more than 2 h, because the EE after
the consumption of oolong tea kept increasing after 2h.
However, the 2 h was the maximum length to measure the EE
when we used the indirect calorimeter with the fasting condition.
As shown in the results, oolong tea increased EE and the
effect was about double that of green tea. Since concentrations
of caffeine and EGCG in oolong tea were about a half of
those in green tea, this suggested that not only caffeine
or EGCG, but also the other components of oolong tea enhanced
EE. Major polyphenols of oolong tea are polymerized polyphenols
produced by its unique fermentation. In the current study,
the concentration of total polymerized polyphenols in oolong
tea (68 mg/300 ml) was much higher than that in green tea
(17 mg/300 ml). These results suggest that polymerized polyphenols
might be the major factor in causing the increase of EE
by oolong tea. Dulloo et al. (20) showed that catechin-polyphenols
affect the sympathetic stimulation of thermogenesis by inhibiting
the enzyme catechol-O-methyltransferase. This mechanism
on the thermogenic effect of catechin-polyphenols is different
from that of caffeine, accordingly, the synergistic interection
between catechin-polyphenols and caffein is suggested. Since
there has been only a few studies that determined the thermogenic
effect of the polyphenols and we have not been able to specify
the polymerized polyphenol(s) that affected EE, further
studies are needed to confirm the mechanism that led to
the larger increase of EE with the consumption of oolong
tea.
In the studies of both Dulloo (15) and Rumpler (16), they
observed an enhancement of the substrate oxidation after
the consumption of those teas. Dulloo (15) reported a small
increase in fat oxidation with the consumption of 150 mg
caffeine but a much greater increase with the consumption
of green tea (33%), indicating that the catechin content
of the tea stimulated the fat oxidation. Rumpler (16) observed
a greater increase in fat oxidation with the consumption
of oolong tea (12%) than that with the consumption of 270
mg caffeine (8%). In the present study, however, the RQ
values were not different among the treatments and remained
constant throughout the study period (Fig. 2). The present
measurement of RQ for 2 h might be too short to determine
the impact of the tea on fat oxidation.
The effect of oolong tea on nutrient absorption may be an
important factor on the weight reduction. There are some
studies that showed the inhibition of fat (21, 22) and carbohydrate
absorption (23). Other studies on this topic would be desirable.
In conclusion, there were some limitations in the current
study, but the results suggested that oolong tea increased
EE and the factor was not only caffeine or EGCG but also
some kinds of polymerized polyphenols.
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