Abstract

Gymnema inodorum (GI), a vegetable widely used in a Northern Thai food, is known for not only its health nourishing effect, but also its hypoglycemic effect. But no scientific evidence on the hypoglycemic effect of GI has ever been reported in human. In this study, the effect of GI consumption on peak plasma glucose concentrations in healthy subjects was investigated. Either oral glucose load (75 g) or standard meal was given to the subjects with respect to the presence or absence of GI consumption and postprandial peak glucose levels were compared. When GI was consumed, 15 min after oral glucose load, the glucose concentration with GI was significantly lower (130 ± 32 vs. 145 ± 27 mg/dl, p < 0.05; N = 73). Doubling dose of GI showed much greater decrease in peak blood glucose concentration than that of the single dose (108 ± 15 vs. 130 ± 32 mg/dl, p < 0.05). When standard meal was used instead of oral glucose load, similar hypoglycemic effect was observed in GI group; 16 out of 20 subjects had a lowered peak glucose concentration (129 ± 27 vs. 147 ± 39 mg/dl, p < 0.05). In order to evaluate the impact of long term GI consumption on plasma glucose concentration and liver function, fasting plasma glucose and liver function test (AST, ALT, GGT and ALP) were monitored at days 0, 2, 4, 7, 14, 21 and 28. The results showed no change in both fasting plasma glucose and liver enzymes. To envisage the mechanism of this hypoglycemic effect, GI leaves were extracted with various solvents and tested for insulinotropic property in INS-1 cells as well as the determination of its inhibition ona-glucosidase activity. Neither increase in insulin level nor inhibition of a-glucosidase enzyme was observed, suggesting that the hypoglycemic effect of GI is involved with other mechanisms than the activation of beta cell or enzymatic inhibition of carbohydrate absorption.

Key words: Gymnema inodorum, hypoglycemic effect, plasma glucose, human, liver function.

Abbreviation

Abbreviations: ALP, Alkaline phosphatase; ALT, alanine transaminase; AST,aspartate transaminase; GI, Gymnema inodorum; GGT, gamma glutamyltransferase; GS, Gymnema sylvestre; OGTT, oral glucose tolerance test.