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Gastroenterology Research and Practice
Volume 2011, Article ID 382852, 6pages
doi:10.1155/2011/382852
Review Article
The Use of Green Coffee Extract as a Weight
Loss Supplement: A Systematic Review and Meta-Analysis of
Randomised Clinical Trials
Igho Onakpoya, Rohini Terry, and Edzard Ernst
Complementary Medicine, Peninsula Medical School, University of Exeter, 25 Victoria Park Road, Exeter EX2 4NT, UK
Correspondence should be addressed to Igho Onakpoya, igho.onakpoya@pcmd.ac.uk
Received 17 June 2010; Accepted 10 August 2010
Academic Editor: Lubos Sobotka
Copyright © 2011 Igho Onakpoya et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
The purpose of this paper is to assess the efficacy of green coffee extract (GCE) as a weight loss supplement, using data from human
clinical trials. Electronic and nonelectronic searches were conducted to identify relevant articles, with no restrictions in time or
language. Two independent reviewers extracted the data and assessed the methodological quality of included studies. Five eligible
trials were identified, and three of these were included. All studies were associated with a high risk of bias. The meta-analytic result
reveals a significant difference in body weight in GCE compared with placebo (mean difference: −2.47 kg; 95%CI: −4.23, −0.72).
The magnitude of the effect is moderate, and there is significant heterogeneity amongst the studies. It is concluded that the results
from these trials are promising, but the studies are all of poor methodological quality. More rigorous trials are needed to assess the
usefulness of GCE as a weight loss tool.
1. Introduction
Overweight and obesity have become a serious health
concern [1]. Different weight management strategies are
presently utilised, and a variety of weight loss supplements
sold as “slimming aids” are readily available. However,
the efficacy of some of these food supplements remains
uncertain. One such supplement is the green coffee extract
(GCE).
GCE is present in green or raw coffee [2]. It is also
present in roasted coffee, but much of the GCE is destroyed
during the roasting process. Some GCE constituents, such
as chlorogenic acid (CGA) can also be found in a variety of
fruits and vegetables [3]. The daily intake of CGA in persons
drinking coffeevariesfrom0.5to1g[4]. The traditional
method of extraction of GCE from green coffee bean, Coffea
canephora robusta, involves the use of alcohol as a solvent
[5]. Extracted GCE is marketed as a weight loss supplement
under a variety of brand names as a weight loss supplement
such as “Coffee Slender”, and “Svetol”.
Evidence is accumulating from animal studies regarding
the use of GCE as a weight loss supplement [6,7]. In
human subjects, coffee intake has been reported to be
inversely associated with weight gain [8]. Consumption of
coffee has also been shown to produce changes in several
glycaemic markers in older adults [9]. Similarly, other
research has indicated that the consumption of caffeinated
coffee can lead to some reductions in long-term weight
gain, an effect which is likely to be due to the known
thermogenic effects of caffeine intake as well as effects of
GCE and other pharmacologically active substances present
in coffee [10]. GCE has also been postulated to modify
hormone secretion and glucose tolerance in humans [11].
This effect is accomplished by facilitating the absorption of
glucose from the distal, rather than the proximal part of the
gastrointestinal tract.
The objective of this paper is to analyse the results of
human clinical trials assessing the efficacy of GCE as a
weight-reducing agent.
2Gastroenterology Research and Practice
2. Methods
Electronic searches of the literature were conducted for
the following databases: MEDLINE, EMBASE, CINAHL,
AMED, and The Cochrane Library. Each database was
searched from inception up until April, 2010. Search terms
used included coffee, green coffee, green coffee extract,
roasted coffee, decaffeinated coffee, chlorogenic acid, caf-
feoylquinic acid, antiobesity agent, appetite suppressant,
abdominal fat, BMI, body mass index, body fat, body
weight, overweight, over weight, corpulen∗,obes
∗,weight
loss, weight decrease, weight watch, weight cycle, weight
control, weight gain, weight maintenance, weight reduc-
tion, weight change, dietary supplement, food supplement,
nutraceutical, nutri∗supplement, over-the-counter OR OTC,
nonprescription drugs, randomised controlled trial, clinical
trial, and placebo. We also searched other internet databases
for relevant conference proceedings, as well as our own files.
Hand searches of the bibliography of retrieved full texts were
also conducted.
Only randomised, double-blind, and placebo-controlled
studies were included in this paper. To be considered for
inclusion, studies had to test the efficacy of GCE for weight
reduction in obese or overweight humans. Included studies
also had to report body weight and/or body mass index
(BMI) as an outcome. No age, time, or language restrictions
were imposed for inclusion of studies. Studies which involved
the use of GCE as part of a combination treatment or not
involving obese or overweight subjects were excluded from
this paper.
Two independent reviewers assessed the eligibility of
studies to be included in the paper. Data were extracted
systematically by two independent reviewers according to
the patient characteristics, interventions, and results. The
methodological quality of all included studies was assessed
by the use of a quality assessment checklist adapted from
the consolidated standard of reporting trials (CONSORT)
guidelines [12,13]. Disagreements were resolved through
discussion with the third author.
Data are presented as means with standard deviations.
Mean changes in body weight were used as common
endpoints to assess the differences between GCE and placebo
groups. Using the standard meta-analysis software [14],
we calculated mean differences (MD) and 95% confidence
intervals (CI). The I2statistic was used to assess for statistical
heterogeneity amongst studies.
3. Results
Our searches produced 2160 “hits”. 328 articles were
excluded because they were duplicate citations, while 767
articles were excluded because of wrong titles and abstracts.
Another 598 articles were excluded because they did not
investigate a food supplements, and 454 articles excluded due
to no report on clinical outcome. A further 13 articles were
excluded due to unsuitable study design. Thus, 5 potentially
relevant articles were identified (Figure 1). One trial was
excluded because it involved only normal weight individuals,
and did not measure weight as an outcome [15]. Another
trial was excluded because it was not randomised [16]. In
effect, 3 randomised clinical trials (RCTs) including a total
of 142 participants met our inclusion criteria, and were
included in this systematic paper [5,17,18]. Their key details
are summarized in Tables 1and 2.
Aforestplot(random-effect model) for the three trials
is shown in figure 2. The meta-analysis reveals a statistically
significant difference in body weight between GCE and
placebo (MD: −2.47 kg; 95% CI: −4.23, −0.72). The I2
statistic of 97% suggests that there is considerable hetero-
geneity amongst the studies. A further plot of two trials
which involved CGA-enriched GCE revealed a statistically
nonsignificant difference in body weight between GCE and
placebo (MD: −1.92 kg; 95% CI: −5.40, 1.56). Heterogeneity
was also considerable in this analysis (I2statistic of 99%).
One of the studies reported a statistically significant decrease
in the percentage of body fat in the GCE group compared
with baseline, but no significant difference in the placebo
group [5]. There was no mention of intergroup differences
regarding the percentage of body fat. None of the trials
reported any adverse events associated with the use of
GCE.
4. Discussion
The main purpose of this systematic paper was to assess
the efficacy of GCE as a weight loss supplement. The
overall meta-analysis revealed a significant difference in
change in body weight between GCE and placebo. The
magnitude of this significance is moderate, and the clinical
relevance is therefore not certain. There is also considerable
heterogeneity amongst the three trials.
In animals, GCE has been reported to influence post-
prandrial glucose concentration and blood lipid concen-
tration [5]. This is thought to be via reduction in the
absorption of glucose in the intestine; a mechanism achieved
by promoting dispersal of the Na+electrochemical gra-
dient. This dispersal leads to an influx of glucose into
the enterocytes [19]. GCE is also thought to inhibit the
enzymatic activity of hepatic glucose-6-phosphatase, which
is involved in the homeostasis of glucose [20]. Reports
from animal studies have suggested that GCE mediates its
antiobesity effect possibly by suppressing the accumulation
of hepatic triglycerides [6]. Some authors have also posited
that the antiobesity effect of GCE may be mediated via
alteration of plasma adipokine level and body fat distribution
and downregulating fatty acid and cholesterol biosynthesis,
whereas upregulating fatty acid oxidation and peroxisome
proliferator-activated receptor alpha (PPARα) expression in
the liver [7].
Diets rich in polyphenols may help to prevent various
kinds of diseases associated with oxidative stress, including
coronary heart disease and some forms of cancer [21,
22]. GCE has been reported to have antioxidant activity,
demonstrated by its ability to scavenge free radicals in vitro,
and to increase the antioxidant capacity of plasma in vivo
[16,23]. There is also evidence that certain dietary phenols,
including GCE, may modify intestinal glucose uptake in a
Gastroenterology Research and Practice 3
Tab l e 1: Methodological characteristics of included studies.
Author Year
Country
Main outcome
(s)
Main
diagnoses of
study
participants
Study
design Gender M/F Randomisation
appropriate?
Allocation
concealed?
Groups
similar at
baseline?
Similar
follow-up
of groups?
Outcome
assessor
blinded?
Care
provider
blinded?
Patients
blinded?
Attrition
bias?
ITT
analysis?
∗Ayton
Research
2009 United
Kingdom
Body weight,
waist, bust and
hip
circumference
Healthy
overweight
subjects
Parallel Unclear ? ?++?????
Thom 2007
Norway
Body weight,
body mass
index
Slight to
moderately
overweight
subjects
Parallel 12/18 ? ?++???
−−
Dellalibera
1998 France
Body weight,
body mass
index
Overweight
volunteers Parallel Unclear ? ?++???
−−
Abbreviation: ITT (intention-to-treat); M/F: Males/Females.
Symbols: ∗: Unpublished study, +:Yes,−:No,?:Unclear.
4Gastroenterology Research and Practice
Tab l e 2: Main results of included RCTs1.
Author Year GCE
specification
No. of
participants
randomised
Age in yrs; Sex:
M/F
Body weight at
baseline
Dosage of
GCE
Treatment
duration
Main results; reported as
means with standard
deviations
Adverse
events
Control for
lifestyle
factors
Ayton Res. 2009
(unpublished)
CGA
enriched
green coffee
62 Not reported
76.65 ±7.25 kg
(GCE) 77.44 ±
12.93 kg (PLA)
180 mg daily 4 weeks
Weight loss was
1.35 ±0.81 kg and
0.12 ±0.27 kg for GCE
and PLA respectively
Not reported Normal
lifestyle
Thom 2007
CGA
enriched
green coffee
30 Not reported
12/18
85.2±4.5kg
(GCE)
84.3±4.3kg
(PLA)
200 mg daily 12 weeks
Mean weight loss was
5.4±0.6 kg (GCE) and
1.7±0.9 kg (PLA). Mean
fat loss was 3.6±0.3%
(GCE) and 0.7±0.4%
(PLA)
No adverse
events
Regular diet,
normal level
of exercise
Dellalibera 2007 Green coffee
extract 50 Range: 19–75 Not reported 200 mg daily 12 weeks
2Mean weight loss was
4.97 ±0.32 kg and
2.45 ±0.37 kg for GCE
and PLA, respectively
Not reported Not reported
Abbreviation: PLA: placebo
1Unless otherwise specified, values are reported as means with standard deviations.
2Values reported as means with standard errors.
Gastroenterology Research and Practice 5
2 articles excluded for the following reasons:
- Only normal weight individuals: 1
3 randomised clinical
trials included
5 full texts retrieved for more
detailed evaluation of the articles
2160 references
retrieved
2155 articles excluded based on duplicate citations;
wrong title/abstract; did not investigate a food
supplement for weight loss; did not report clinical
outcome; or the study design was unsuitable
- Nonrandomised study: 1
Figure 1: Flow chart for inclusion of randomised clinical trials.
Ayton 2009
Dellalibera 2007
Thom 2007
−1.35
−4.97
−5.4
0.81
1.75
0.6
30
30
15
−0.12
−2.45
−1.7
0.27
1.66
0.9
32
20
15
34.6%
31.6%
33.8%
−1.23 [−1.53, −0.93]
−2.52 [−3.48, −1.56]
−3.7 [−4.25, −3.15]
−10 −50 510
Favours GCE Favours placebo
100%
Total (95% CI)
Test for overall effect: Z=2.76 (P=.006)
75 67
Study or subgroup Mean Mean
GCE
SD SDTotal Total Weight
Mean difference
IV, random, 95% CI
Mean difference
IV, random, 95% CI
−2.47 [−4.23, −0.72]
Placebo
Heterogeneity: τ2=2.3; χ2=61.66, df =2(P<.00001); I2=97%
Figure 2: Forest plot showing the effect of GCE on body weight.
number of ways [8,24]. This activity might provide a basis
for explaining its effects on body weight. The purported
slimming effect of GCE would have a protective effect against
diabetes mellitus, via changes in gastrointestinal hormone
secretion [10]. A few questions, however, arise from the RCTs
which involve the use of GCE as a weight loss aid.
All the RCTs involving the use of GCE which have been
conducted so far have very small sample sizes, with the largest
number of participants being 62 in one trial [17]. These
small sample sizes increase the possibility of spurious or false
positive results. Two of the RCTs were unclear about drop-
outs of participants from the trial; neither did they report
on intention-to-treat analysis [17,18]. All of the trials so far
identified have been of very short duration. This makes it
difficult to assess the efficacy and safety of GCE as a weight
reduction agent on the medium to long-term. Although
none of the RCTs identified reported any adverse events,
this does not indicate that GCE intake is “risk-free”. Two
participants in a study report dropped out due to adverse
events associated with the intake of GCE [16]. These included
headache and urinary tract infection. Thus, the safety of this
weight loss aid is not established.
The effective dosage of GCE for use as a weight loss
supplement is also not established. The dosages of GCE
reported in most of the human trials identified were
estimated, as the GCE was a component of coffee. While 2
of the RCTs identified enriched their GCE with CGA [5,17],
the third trial did not report that the GCE used was fortified
with CGA [18]. This warrants further investigation.
The RCTs identified from our searches were not also
clear on blinding issues. None of the RCTs reported on
how randomisation was carried out, and none provided
information regarding blinding of outcome assessors. This
casts doubt on the internal validity of these trials. Future
trials involving the use of GCE as a weight loss supplement
should be conducted in line with the CONSORT guidelines.
This will ensure the validity and applicability of study results.
Two authors in one study were affiliated to a company which
marketsSvetol[18] but did not specify whether or not they
had any conflicts of interest.
6Gastroenterology Research and Practice
This systematic review has several limitations. Though
our search strategy involved both electronic and nonelec-
tronic studies, we may not have identified all the available
trials involving the use of GCE as a weight loss supplement.
Furthermore, the methodological quality of the studies
identified from our searches is poor, and all are of short
duration. These factors prevent us from drawing firm
conclusions about the effects of GCE on body weight.
5. Conclusion
The evidence from RCTs seems to indicate that the intake of
GCE can promote weight loss. However, several caveats exist.
The size of the effect is small, and the clinical relevance of this
effect is uncertain. More rigorous trials with longer duration
are needed to assess the efficacy and safety of GCE as a weight
loss supplement.
Conflict of Interests
I. Onakpoya is funded by a grant from GlaxoSmithKline. The
funder had no role in the preparation of the paper. R. Terry
and E. Ernst declare no potential conflict of interests.
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