Gymnema Sylvestre is a herb native to the tropical forests of southern and central India and Sri Lanka.
Chewing the leaves suppresses the sensation of sweetness. This effect is attributed to the eponymous gymnemic acids. Gymnema Sylvestre has been used in herbal medicine as a treatment for diabetes for nearly two millennia, and though there is insufficient scientific evidence to draw definitive conclusions about its efficacy two small clinical trials have shown Gymnema to reduce glycosylated hemoglobin levels. Common names include Gymnema, cowplant, Australian cowplant, gurmari, gurmarbooti, gurmar, Periploca of the woods, meshasringa, and miracle fruit(also a common name for two unrelated plants).
While it is still being studied, and the effects of the herb are not entirely known. Gymnema reduces the taste of sugar when it is placed in the mouth. From the extract of the leaves were isolated glycosides known as gymnemic acids, which exhibit anti-sweet activity. This effect lasts up to about 2 hours.
Some postulate that the herb may block sugar receptors on the tongue. This effect was observed in isolated rat neurons. The active ingredients are thought to be the family of compounds related to gymnemic acid: purified gymnemic acids are widely used as experimental reagents in taste physiology and have also an anti-diabetic effect in animal models, reduce intestinal transport of maltose in rats when combined with acarbose, and reduce the absorption of free oleic acid in rats. Historically, the leaves were used for stomach ailments, constipation, water retention, and liver disease; However, these claims are not supported by scientific studies.
Clinical trials with type 2 diabetics in India have used 400 mg per day of a water-soluble acidic fraction of the Gymnema leaves administered for 18 -20 months as a supplement to the conventional oral drugs. During GS4 supplementation, the patients showed a significant reduction in blood glucose, glycosylated haemoglobin, and glycosylated plasma proteins, and conventional drug dosage could be decreased. Five of the 22 diabetic patients were able to discontinue their conventional drug and maintain their blood glucose homeostasis with GS4 alone.
These data suggest that the beta cells may be regenerated/repaired in Type 2 diabetic patients on GS4 supplementation. This is supported by the appearance of raised insulin levels in the serum of patients after GS4 supplementation. Though for the moment G. Sylvestre cannot be used in place of insulin to control blood sugar by people with either type 1 or type 2 diabetes, further evidence of its positive effect is accumulating[ Source: Wikipedia