The aim of this systematic review is to examine the efficacy of Garcinia extract, hydroxycitric acid (HCA) as a weight reduction agent, using data from randomised clinical trials (RCTs). Electronic and nonelectronic searches were conducted to identify relevant articles, with no restrictions in language or time. Two independent reviewers extracted the data and assessed the methodological quality of included studies. Twenty-three eligible trials were identified and twelve were included. Nine trials provided data suitable for statistical pooling. The meta-analysis revealed a small, statistically significant difference in weight loss favouring HCA over placebo (MD: −0.88 kg; 95% CI: −1.75, −0.00). Gastrointestinal adverse events were twice as common in the HCA group compared with placebo in one included study. It is concluded that the RCTs suggest that Garcinia extracts/HCA can cause short-term weight loss. The magnitude of the effect is small, and the clinical relevance is uncertain. Future trials should be more rigorous and better reported.
The prevalence of overweight and obesity has increased over the last decade [1 ], and current measures have not been able to stem the tide. A wide variety of weight management strategies are presently available, and some involve the use of dietary supplements marketed as slimming aids. One such slimming aid is Garcinia extract, (-)-hydroxycitric acid (HCA).
HCA is a derivative of citric acid and can be found in plant species native to South Asia such as Garcinia cambogia, Garcinia indica, and Garcinia atroviridis [2 ]. HCA is usually marketed as a weight loss supplement either alone or in combination with other supplements [2. 3 ]. Some authors have suggested that HCA causes weight loss by competitively inhibiting the enzyme adenosine triphosphatase-citrate-lyase [3 –6 ]. HCA has also been reported to increase the release or availability of serotonin in the brain, thereby leading to appetite suppression [7 ]. Other postulated weight loss mechanisms include inhibition of pancreatic alpha amylase and intestinal alpha glucosidase, thereby leading to a reduction in carbohydrate metabolism [8 ].
Animal studies have suggested that HCA causes weight loss [3. 9 ], and human trials involving the use of HCA as a weight loss supplement have been carried out [3 ].
The primary objective of this systematic review was to examine the efficacy of HCA in reducing body weight in humans, using data from randomised clinical trials.
Electronic searches of the literature were conducted in the following databases: Medline, Embase, The Cochrane Library. Amed, and Cinahl. The search terms used included dietary supplements, antiobesity agents, body weight, hydroxycitrate, garcinia. and derivatives of these. Each database was searched from inception until March, 2010. We also searched the Internet for relevant conference proceedings and hand searched relevant medical journals, and our own files. The bibliographies of all
located articles were also searched.
Only randomised, double-blind, placebo-controlled studies were included in this paper. To be considered for inclusion, studies had to test the efficacy of oral HCA or any of its salts for weight reduction in obese or overweight humans. Included studies also had to report body weight as an outcome. No age, time, or language restrictions were imposed for inclusion of studies. Studies which involved the use of HCA as part of a combination treatment (dietary interventions containing other supplements in addition to HCA), or not involving obese or overweight subjects based on body mass index (BMI) values, 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 [10. 11 ]. In addition, the Jadad score [12 ] was also used to assess the quality of included studies. Disagreements were resolved through discussion with the other authors.
Data are presented as means with standard deviations. Mean changes in body weight were used as common endpoints to assess the differences between HCA and placebo groups. Using the standard meta-analysis software [13 ], we calculated mean differences (MDs) and 95% confidence intervals (CIs). Studies included in the meta-analysis were weighted by SD (a proxy for study size). If a trial had 3 arms, only the HCA and placebo arms were included in the meta-analysis. The I 2 statistic was used to assess for statistical heterogeneity amongst studies. A funnel plot was used to test for publication bias.
Our searches produced 5002 “hits” of which 23 potentially relevant articles were identified ( Figure 1 ). Six trials were excluded because they involved the use of HCA in combination with other therapies [7. 14 –18 ]. One trial was excluded because it was not blinded [19 ], and another because it was single blinded [20 ]. Two articles were excluded because they were duplicates. One of these articles [21 ] was the same trial published in another journal which had been earlier excluded, while the other article [22 ] was a report of two individual trials which were included in this systematic review. One trial was excluded because the investigators did not measure weight as an outcome [23 ]. Thus 12 randomised clinical trials (RCTs) including a total of 706 participants met our inclusion criteria, and were included in this systematic review [2. 4 –6. 24 –31 ]. Their key details are summarized in Tables Tables1, 1. ,2, 2. and and3. 3.