The objective of this systematic review was to assess the efficacy and effectiveness of HCA as a weight reduction agent. The overall meta-analysis revealed a small difference in change in body weight between the HCA and placebo groups. The effect is of borderline statistical significance and is no longer significant on the basis of a sensitivity analysis of rigorous RCTs. Arguably the overall effect size is also too small to be of clinical relevance. The overall meta-analytic result corroborates the findings from one of the studies without suitable data for statistical pooling [31
], but is at variance with another study [4
The overall result should be interpreted with caution. The pooled data from some of the studies were adjusted values. Three studies with small sample sizes [6
] seemed to have influenced the overall meta-analytic result in favour of HCA over placebo. If these three trials are excluded, the meta-analysis result is no longer significant. The largest and most rigorous RCT [25
] found no significant difference in weight loss between HCA and placebo.
The result of our systematic review corroborates the findings from a previous systematic review of weight loss supplements, which reported that the weight reducing effects of most dietary supplements is not convincing [32
]. HCA is a commonly marketed as a complementary weight loss supplement. The meta-analysis from this systematic review suggests that HCA is not as effective as conventional weight loss pills, for example, orlistat. In a meta-analysis report of 16 studies including over 10
000 participants [33
], overweight and obese patients taking orlistat had a clinically significant reduction in body weight compared to placebo (MD: 2.9
kg; 95% CI: 2.5, 3.2). Participants taking orlistat achieved a 5% and 10% weight loss compared to placebo in the results from pooled data. This contrasts quite sharply with the results from the meta-analysis of HCA clinical trials.
All of the studies included in this review had methodological issues, which are likely to have affected the outcomes in these trials. This is supported by the I2
values from the overall meta-analysis result which suggested substantial heterogeneity. Most of the studies included in this systematic review had small sample sizes. Only one included study [25
] reported that they performed a power calculation. Larger study sizes with a priori
sample size calculation will help eliminate a type II error (i.e., failure to reject the null hypothesis when it should have been rejected). Only one study [25
] performed an intention to treat (ITT) analysis, while all the participants in three other studies [24
] were reported to have completed the trial. The failure of about 66% of the included studies to report ITT analyses casts a doubt as to the validity of their results. In several of the RCTs, drop-outs/attrition was unclear. In one study [5
], participants were excluded due to mixed-pill ingestion (an error in coding of pill bottles resulted in some participants receiving a mixture of HCA and placebo). Male participants were also excluded from the analysis of this RCT because they were too few in number compared with females in the trial. It was also unclear to which intervention group the excluded participants belonged to in this study.
The dosage of HCA, and the duration of study also varied amongst the RCTs. The dosage of HCA used ranged from 1
g to 2.8
g daily. The optimal dose of HCA is currently unknown. Two included studies which differed widely in results [25
] also differed widely in dosage of HCA. Though one of these studies claimed the bioavailability of the HCA used in their trial was high [25
], the dosage of HCA used was almost twice that used in the other trial [29
]. It is not clear if the higher HCA dosage ensures a higher bioavailability of HCA. A nonlinear, significant (P
< .05) correlation between the dosage of HCA and body weight loss seems to exist (). Garcinia cambogia
was the main source of HCA in most studies, with Garcinia atroviridis
being the source of HCA in one included study [2
]. None of the trials used Garcinia indica
as an intervention. It is unclear if the strain of Garcinia
species influences the bioavailability of HCA. Furthermore HCA is also reported to be found in Hibiscus subdariffa
], and none of the studies included in this review used HCA extracted from this plant species. The duration of the studies included in the review also differed, with a range of 2 to 12 weeks, and mode of 8 weeks. This is probably too short a time to assess the effects of HCA on body weight.
Effect of dosage of HCA on body weight. The dosages from included RCTs did not produce a linear effect on body weight.
There was some variation in the design of the RCTs included in the review. All of the studies included had parallel-study designs except two which were crossover trials [26
]. Four included RCTs comprised three intervention groups [6
]. None of the included studies indicated whether or not outcome assessors were blinded, and seven studies did not specify the source of funding [2
]. The failure of study investigators to adhere strictly to the CONSORT guidelines [10
] may have contributed to the variation in methodology (and heterogeneity) of the trials included in the review.
Most (7/12) RCTs reported adverse events, with headache, nausea, upper respiratory, and gastrointestinal tract symptoms being the most frequent ones. In most of the trials, there were no significant differences in adverse events between HCA and placebo. This seems to corroborate the report in another article [34
] which suggested that HCA is safe for human consumption. A few of the studies reported a positive effect of HCA on the blood lipid profile [6
], while one did not find any significant difference between HCA and placebo on this blood parameter [2
]. However, given the short duration of the studies involving the use of HCA, it is unclear how safe this dietary supplement is on the intermediate and long term. In 2009, the Food and Drug Administration (FDA) warned consumers about the potential for serious adverse effects associated with the consumption of hydroxycut, a popular HCA-containing slimming pill. This resulted in the withdrawal of this supplement from the market [35
All of the studies included in this review except two [26
] incorporated some form of dietary control into their trials, with participants in one study receiving high fibre diets [25
]. The daily caloric intake for participants in the trials included in this review ranged from as low as 1,000
], to as high as 3,009
]. Half the number of studies in this review did not institute any form of exercise. The extent to which the variation in these lifestyle adjustment factors could have influenced study results is uncertain. Two studies [28
] reported a significant reduction in appetite in the HCA group (P
< .001), but not with placebo. Three other studies did not find any significant difference between HCA and placebo groups in terms of satiety effect [5
All of the studies described their participants as overweight, obese, or both. However, in one RCT [2
], the definition of the participants as obese individuals is questionable, because they had a BMI between 25–30
. Based on the World Health Organisation definition [36
], a BMI between 25–29
is considered overweight, while a BMI ≥ 30
is termed obese.
This systematic review has several limitations. Though our search strategy involved both electronic and non-electronic studies, we may not have identified all the available trials involving the use of HCA as a weight loss supplement. Furthermore, the methodological quality of most of the studies identified from our searches is poor, and most studies are of short duration. These factors prevent us from drawing firm conclusions about the effects of HCA on body weight.