Garcinia cambogia is the plant commonly referenced as garcinia, citirn, cambooge or Tamarind, and is a member of the Clusiaceae family. It is native to Southeastern Asia where it has been used for centuries as a food preservative, flavoring agent and carminative. The fruit of the plant is yellow, about the size of an orange, and has a thin skin with deep furrows.  The rind of the fruit is the part of the plant emplyed for various medicinal applications. Garcinia does not have a long history of use in Western Herbalism, but has gained interest due to its effects on fat metabolism and appetite suppression.
The principle constituent in garcinia is hydroxycitric acid (HCA), or hydroxycitrate. This important component makes up 10 - 30% of the dried fruit rind. Garcinia is discussed essentially in terms of hydroxycitrate, with the majority of research focusing on this chemical compound. Garcinia also contains a significant amount of beneficial flavonoids.
The exact mechanisms of action for hydroxycitrate’s effect on physiologic and metabolic processes are not fully known. Early studies showed that it inhibits the formation of fat in animals. [2, 3] HCA was shown to be a potent inhibitor of ATP citrate lyase, an enzyme that catalyzes the extramitochondrial cleavage of citrate to oxaloacetate and acetyl-CoA:
- citrate + ATP + CoA –> acetyl-CoA + ADP + P(i) + oxaloacetate - 
The significance of this metabolic reaction is that inhibition limits the availability of acetyl-CoA units required for fatty acid synthesis and lipogenesis; especially when a diet high in carbohydrates is consumed. Furthermore, extensive animal studies indicated that (-)-HCA suppresses food intake and may actually induce weight loss. [4, 5]
Hydroxycitrate also appears to exert effects on processes other than fuel metabolism. One study in rats showed that hydroxycitrate can inhibit [3H]-5-HT (hydroxy-tryptophan) uptake, while also increasing 5-HT availability in isolated brain cortical slices; similar to the way SSRIs (selective serotonin reuptake inhibitors) work. The authors conclude that these effects may be applicable in controlling appetite, as well as treatment of depression, insomnia, migraine headaches, and other serotonin-deficient conditions. 
A novel derivative of hydroxycitrate, called Super Citrimax or HCA-SX, has been commonly used in research studies. It appears to be safe when taken orally and has demonstrated bioavailablity in human plasma when studied by gas chromatography-mass spectrometry. 
As mentioned, most of the research on garcinia has been linked to its effect on curbing appetite and inhibiting body fat biosynthesis. The majority of studies have been conducted either in vitro or in vivo using animal models. There are, yet, few positive articles published in human subjects that are large enough and designed well enough.
Data from animal studies suggest Garcinia may be of benefit in disorders of glucose metabolism and also obesity. Garcinia and the isolated hydroxycitrate have demonstrated favorable effects on glucose, insulin, and lipid metabolism in animal studies. A study in mice given a 3.3% Garcinia cambogia extract demonstrated reduced levels of serum insulin and leptin, as well as the leptin/WAT ratio, versus control.  Furthermore, glucose metabolism was improved and leptin-like activity was exhibited. Another animal study showed that hydroxycitrate suppresses de novo lipogenesis and may improve glucose tolerance. 
The derivative compound, Citrimax or HCA-SX, proved to be effective in restricting body weight gain in adult rats. The results of another animal study showed that at doses relevant for human consumption, dietary HCA-SX significantly contained body weight growth. Again, in this study leptin levels were affected. However, in this particular case study, lowered abdominal fat leptin expression was observed while plasma leptin levels remained unaffected. This study also identified a small set (approximately 1% of all genes screened) of specific genes found in fat tissue that are sensitive to dietary HCA-SX. Vital genes for transcribing mitochondrial/nuclear proteins were not affected. The results also showed that HCA-SX-sensitive genes upregulated genes encoding serotonin receptors, which is unique to this compound. 
The one well-designed, double-blind, placebo-controlled study of the use of garcinia in humans that has been published was not supportive.  This study found that garcinia was no more effective than placebo for overall body weight and/or fat weight loss. Problems with the experimental design include lack of measurement of appetite suppressant effect or the bioavailability of hydroxycitric acid to the bloodstream, as well as the use of a high fiber diet that may have influenced bioavailability of HCA.  A review of natural products for obesity concluded that the best available human data indicates that this garcinia is no more effective than placebo. 
A novel application for garcinia is in the treatment of peptic ulcers. A study in rats that were pretreated with a G. cambogia fruit extract (1 g/kg body weight/day at interval of 7 and 15 days) demonstrated a protective effect on gastric mucosa against HCl-ethanol induced damage. The extract decreased the volume and acidity of gastric juice. The authors conclude that due to garcinia’s ability to decrease acidity and increase mucosal defense, it is a potential anti-ulcer agent.  Another study showed similar results with indomethacin induced gastric damage. 
Garcinia, in combination with some other botanicals, has also demonstrated lipid lowering activity in rats. In one study, flavonoids from Cocos nucifera, Myristica fragrance, Saraka asoka and Garcinia cambogia exerted maximum hypolipidaemic activity at a flavonoid level of 10 mg/kg BW/day from Garcinia cambogia. Interestingly, higher doses were less effective in reducing lipid levels in serum and tissues, which were shown not to exert toxicity. 
In addition, garcinia may aid endurance during post-absorptive aerobic exercise by promoting gluconeogenesis; may be beneficial in hypertension, dyslipidemias, diabetes mellitus, and metabolic syndrome. As previously stated, its most popular application remains in controlling appetite, as well as in treatments of depression, insomnia, migraine headaches, and other serotonin-deficient conditions. [16, 17, 6]
Dosages are always dependent on the preparation. Most of the research has been conducted in animals, so doses that are effective in humans have not yet been fully determined. However, a typical dose of hydroxycitrate is 500 milligrams, three times daily . As well, a low fat diet should be maintained when taking this supplement for weight loss.
Long-term toxicity studies in humans are lacking. Most of the data on toxicity of Garcinia extracts comes from animal research. A review published in 2004 stated that acute oral toxicity studies in animals demonstrate that CitriMax (50% HCA as calcium salt) has a low acute oral toxicity. Doses up to 2500 mg/kg/day in rats for a period of 90 days caused a significant decrease in body weight and reduction in feed consumption without any adverse effects. 
Additionally, the authors of this recent research review concluded that based on its structure, mechanism of action, and long history of use, HCA is unlikely to cause reproductive or developmental effects. The animal study demonstrated that the 90 day treatment with HCA-SX (CitriMax) does not cause any changes in major organs or in hematology, clinical chemistry, and histopathology. 
One case report of rhabdomyolysis following the ingestion of a weight-loss herbal medicine, containing Garcinia cambogia, in an otherwise healthy 54-year-old woman has been published.  Serum creatine kinase (CK) was elevated. The condition resolved when the supplement was discontinued. As this was a combination product, it is unknown which component was causative.
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