Hydroxycitric acid (HCA) is a chemical (derivative of citric acid) that is found in a variety of tropical fruits Garcinia cambogia, Garcinia indica (Kokum), Hibiscus subdariffa, and Garcinia atroviridis (Asam gelugor). Hydroxycitric acid is sold as a fat burner, regulator of appetite and carbohydrate metabolism and as healthy digestion aid. It is now incorporated into many commercial weight loss products.
Recommended Dose and How to Take
Recommended doses by manufacturers vary from 250 – 1.000 mg per serving up to 3 times daily. In experimental studies, doses ranging from 1.000 mg to 2.800 mg daily are used.
Weight Loss Effects
Hydroxycitric acid has been reported to suppress appetite via increasing the release or availability of serotonin in the brain . Some authors suggested that HCA causes weight loss by inhibiting the enzyme ATP-citrate-lyase (an extra-mitochondrial enzyme involved in the initial steps of fat formation) [2-4]. This also limits the availability of acetyl coenzyme A (acetyl CoA) for lipid synthesis during carbohydrate feeding . Animal studies are also suggesting that chronic HCA feeding promotes lipid oxidation and spares carbohydrate utilization in mice at rest and during running .
In a rigorous controlled trial  which evaluated the effectiveness of G. cambogia extract (50% hydroxycitric acid by chemical analysis) for weight loss and fat mass reduction with a total of 135 subjects, no significant differences (in weight loss as well as body fat mass loss) were observed after 12 weeks of treatment. In a meta-analysis from 2010  failed to draw a firm conclusion based on available data at that time. Researchers did report a small difference in change in body weight with HCA supplementation but warned about limitations of studies examined.
Does Hydroxycitric Acid Improve Exercise?
Hydroxycitric acid is claimed to improve exercise performance by limiting the use of stored energy in the muscles, which in return prevents fatigue. This is achieved via its ability to increase fatty acid oxidative capacity . These results of a study by Kriketos and colleagues  does not support the hypothesis that 3.000 mg of HCA affects energy expenditure, either during rest or during moderately intense exercise. Subjects in this study consumed a typical western diet composed of 30-35% fat. While on the other hand, Kyoko et al.  reported that short-term ingestion of 500 mg daily HCA for 5 days increases fat oxidation during moderate intensity exercise. Kyoko and colleagues suggested that HCA ingestion increases the fat oxidation capacity and spares carbohydrate use during the same-intensity exercise even in untrained men.
A study  that evaluated the effects of chronic hydroxycitric acid administration (10 mg twice/day) on endurance exercise in mice, reported that HCA promoted the accumulation of glycogen in skeletal muscle (16 h after administration), significantly increased maximum swimming time (after 3 days of oral administration), increased lipid oxidation with spared carbohydrates.
Recently, a small-scale study (8 healthy male volunteers) has shown that oral HCA supplementation increases glycogen synthesis in exercised human skeletal muscle and lowers insulin response under oral glucose challenge .
Hydroxycitric acid has also been shown to affect the whole-body insulin sensitivity by significant down-regulation of the insulin-regulated glucose transporter (GLUT4) and up-regulation of fatty acid translocase (FAT/CD36) . This new study provides some evidence that HCA supplementation provides additional benefit to improve insulin sensitivity in humans. However, it should be noted that increasing fat oxidation after HCA supplementation could have a risk of increasing ketosis for patients with severe diabetes.
In clinical trials, gastrointestinal adverse events were twice as common in subjects taking hydroxycitric acid compared with placebo . Other side effects from randomized clinical trials include a headache, skin rash and common cold. Some studies even reported adverse events on a daily basis, however without any serious or severe adverse events . No treatment-relevant changes were observed in 10 healthy male volunteers after administering HCA at a dose of 3.000 mg daily for 30 days . Another study  also examined the same dose of HCA in 48 patients and also reported no severe side effects.
In subchronic animal studies, administration of high doses of certain HCA-containing preparations led to testicular toxicity (testicular atrophy and impaired spermatogenesis) . So, based on available toxicological data, the main health concern associated with the use of HCA refers to a male reproductive system. However, human data are currently insufficient to conclude on the safety of HCA with regard to the human male reproductive system .
There is also a case study of a patient with Garcinia cambogia-associated hepatic failure, which required a transplant .
(Other Common Names: HCA, Hydroxycitrate, 1,2-Dihydroxypropane-1,2,3-tricarboxylic acid, Garcinia Extract, Kokum Extract, Asam Gelugor Extract, Garcinia cambogia fruit rind extract, Garcinia indica fruit rind extract, Garcinia atroviridis fruit rind extract, Slim339®)
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