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International Journal of Biotechnology and Biomedical Sciences
Volume 1, Number 1; July- December, 2015 pp. 21-24
© Krishi Sanskriti Publications
http://www.krishisanskriti.org
Green Tea and Weight Loss:
An update (Meta-Analysis)
Poonam Pawar
Sir H N Medical Research society, Sir H N Reliance Foundation Hospital and Research Centre
E-mail: poonam.pawar@rfhospital.org
Abstract—Obesity is the growing health disorder globally and
lifestyle changes are at the heart of this problem. It has been found
that green tea market is increasing. One of the supposedly many
effects of green tea is the weight loss. There is vast literature
available related to this subject. The purpose of this study was to
elucidate by meta-analysis whether green tea has an effect on body
weight. PubMed search was done for the term - Green tea and later
limited by English-language, human studies published in last decade
and available as full text. Out of the 704 initially retrieved articles 11
were included in the present meta-analysis after considering the
exclusion and inclusion criteria of the study. The pooled results of all
the studies with the random effect model is -1.26 [-1.87 to -0.65]. It is
imperative by this meta-analysis that green tea consumption leads to
weight loss. However the substantial heterogeneity (I2 = 81.71%)
among the studies warranties larger studies for confirmation and
validation of the effect of green tea on weight of an individual.
Keywords: Green Tea, Weight Loss, Meta-Analysis
1. INTRODUCTION
Obesity is a growing health issue worldwide. According to
world health organization (WHO) report updated in January
2015 (a) prevalence of obesity has more than doubled since
1980 (b) 600 million adults are obese and 39% are overweight
as per the 2014 statistics (c) obesity is also prevalent in
children under age 5, according to 2013 statistics it accounts to
42 million [1].
Specifically in India there is a growing prevalence of obesity.
India is third most obese country in the world, just behind US
and China [2]. India is a developing country with 270 million
people under poverty line. In such a scenario the rise in
obesity and obesity related disorders focuses on the increasing
effect of Lifestyle changes specifically eating habits i.e. more
consumption of junk food [3].
The solution to this problem is to have healthy lifestyle
speaking of which opens a lot of doors from exercise to food.
India is the world’s largest Tea-drinking nation and there is an
emerging trend of drinking green tea is observed specifically
for the reasons of weight loss [4]. There is increase in the
demand of green tea in Indian market [5].
Asians have been aware of health benefits of green tea for
over a century [6] and for almost 24 years now, it is has been
considered as enhancer of energy expenditure and fat
oxidation and thereby inducing weight loss (WL) [7,8]. The
polyphenols in green tea such as EpiGalloCatechin Gallate
(EGCG) stimulates energy expenditure because it has
thermogenic effect as proven by a couple of short-term studies
showing significant increase in energy expenditure and fat
oxidation [9, 10]. Later on the longer term studies were
published on the effect from an EGCG–caffeine mixture on
WL.
Hence a lot of literature is generated in context to green tea
and weight loss. Therefore this study aimed to find out
whether green tea has effect on body weight through meta-
analysis of the available literature.
2. METHODOLOGY
2.1 Identification of Relevant Studies
PubMed was searched for the term – Green tea.
The search was limited to English language and human
studies. All the studies available as free full text articles for
the past decade.
2.2 Inclusion and exclusion criteria
A study was included in the review if (a) the study participants
were randomly assigned to conditions, (b) the results allowed
a direct comparison of the effects of green tea consumption
(either dosage versus placebo or high dosage versus low
dosage) on either WL or WM, and (c) the study lasted at least
for 8 weeks. Green tea is served as either regular tea or as
capsules.
An important exclusion criterion was the use of any tea other
than an EGCG–caffeine mixture (such as oolong tea).
2.3 Data extraction
We extracted data for various parameters from the original
articles using a standardized data extraction form. Wherein the
study’s author(s), year of publication, the duration of the
Poonam Pawar
International Journal of Biotechnology and Biomedical Sciences
Volume 1, Number 1; July- December, 2015
22
treatment phase (weeks), the age range, average body weight
and gender of the participants in the study was recorded. We
also recorded the number of participants and the dosage of
green tea administered (mg/day).
For each condition, we calculated or extracted the mean
weight change (kg) between the post-treatment and the
baseline assessment. For studies which mentioned WL and/or
WM the baseline corresponded to the time immediately before
starting of WL phase and /or WM phase respectively. The
post-treatment mean was recorded just after the intervention
ends. Irrespective of the study design, negative values for the
mean change, indicate WL, a value of zero indicates no
change, and positive values indicate an increase in the body
weight on average. The effect size measure for the
Metaanalysis was therefore difference between values of the
mean change for the treatment minus the mean change value
for the control group.
2.4 Statistical Analysis
The results are represented as weighted mean of the body
weights (kg) of the study participants. The Meta-Analysis is
performed using Exploratory Software for Confidence
Intervals, ESCI software. The effect size estimates were
aggregated based on a random effects model to estimate the
amount of heterogeneity in the effect sizes. We report the
estimated average effect (µ), the estimated amount of
heterogeneity (τ), and the estimated percentage of the total
amount of variability that can be attributed to heterogeneity
(I2). Corresponding 95% confidence intervals are given for all
of these statistics.
3. RESULTS
Initially 48 potentially relevant articles were retrieved.
These articles where then assessed on the basis of titles and
abstract thereby excluding in vitro studies, unrelated studies,
biochemical and molecular biology based studies..
Further review articles which didn’t contribute any additional
data were excluded. Also articles having any of the following
insufficiencies: 1) animal studies 2) full text in language other
than English 3) insufficient data; were excluded. The relevant
data from two studies was requested from the corresponding
authors through e-mail but could not be procured. Hence these
two studies could not be included in this review. None of these
studies were excluded due to lack of blinding. After this
rigorous screening, 10 articles are included in this review [13-
22]. Fig. 1 summarizes the selection procedure of these
articles.
More than one effect size could be calculate from two studies.
Hursel et al. [14] provided two effect sizes corresponding to
two sub-groups viz. adequate protein (AP) diet and high-
protein (HP) diet under green tea-caffeine mixture
consumption and placebo groups in WL and later WM. Also
Wang et al. [15] study group provided three effect size
estimates as a result of three treatment groups wherein
participants received increasing order of dosage as a result of
different number of servings. Therefore a total of 13 effect
size estimates could be extracted from the 9 studies. Fig. 2
shows a forest plot of the individual effect size estimates with
corresponding study weightings and 95% confidence intervals.
The random-effects model indicated a modest, but significant
positive effect of catechins on WL (µ = -1.26, 95% CI: -1.87
to -0.65; p = 0.01). Therefore, it is estimated that subjects in
the treatment groups lost on average 1.26 kg more weight (or
gained on average 1.26 kg less weight) than people in the
control groups [Fig. 2].
Removal of any individual study from the meta-analysis did
not alter this conclusion. However, the results were clearly
heterogeneous (I2 = 99.53%, p= 0.01; τ = 1.061 kg, 95% CI:
0.98, 1.15).
4. DISCUSSION
This meta-analysis shows green tea consumption has a
negative impact of body weight of an individual even when
consumed as an EGCG-caffeine mixture. Also the results
show that difference in dosage of catechins in the EGCG–
caffeine mixture among treatment and control groups had no
effect on overall effect size estimates of this meta-analysis.
Green Tea and Weight Loss: An update (Meta-Analysis) 23
International Journal of Biotechnology and Biomedical Sciences
Volume 1, Number 1; July- December, 2015
This result is in line with study by Berube-Parent et al. [10]
wherein different mixtures of EGCG and caffeine with a
different dosage of catechins were examined. The results from
that study showed that all mixtures increased 24-h energy
expenditure and that the increase was similar for all doses of
EGCG in the mixtures, which was also found in the study
from Wang et al. [15].
It is important to note all the studies included in this particular
meta-analysis had comparable designs: in the WL studies [13–
22] participants immediately started to consume an EGCG–
caffeine mixture for 8-12 weeks following randomization. All
studies had test period for at least 12-13 weeks except for
Tsuchida T et al. [21] that had a test period of 8 weeks. Two
WM studies [14, 20] had participants with first weight loss
phase for 4 weeks using a very low energy diet, followed by
randomization and then an EGCG–caffeine mixture
supplementation phase for either 12 or 13 weeks. One study
[16] randomly assigned subjects to three different dosage
conditions as compared to controls. All the studies had true
placebo group except one [22] made the comparison between
two groups of low and high dosage of catechins.
However there was significant heterogeneity observed in this
meta-analysis. Therefore there was a need to look up for
factors influencing meta-analytical heterogeneity. Two factors
were highlighted from the data provided in the research
articles included in this review which are ethnicity and
habitual caffeine intake. It is noted that Asian studies had a
low caffeine intake and while almost all Caucasian studies had
a high caffeine intake. Although caffeine intake was not a
significant moderator alone but when examined together in a
model including ethnicity it was found have an impact. If
more studies with both ethnicities with different amounts of
caffeine intake are conducted and then a similar meta-analysis
would provide a clearer picture of the effectiveness of these
moderators.
5. CONCLUSION
Taken together, this meta-analysis has shown that EGCG–
caffeine mixtures have a positive effect on WL and on WM.
Moreover, it also shows that habitual caffeine intake and
ethnicity may be moderators, whereas different doses of
catechins do not have a significantly different effect.
6. ACKNOWLEDGEMENTS
Medical Research Society of Sir H N Reliance Foundation
Hospital and Research Centre for providing necessary
infrastructure for this review writing.
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