Bitter melon (Momordica charantia) reduces adiposity, lowers serum insulin and normalizes glucose tolerance in rats fed a high fat diet.

Bitter melon (BM) is known for its hypoglycemic effect but its effect on rats fed a hyperinsulinemic high fat diet has not been examined. In a dose-response (0.375, 0.75 and 1.5%) study, oral glucose tolerance was improved in rats fed a high fat (HF; 30%) diet supplemented with freeze-dried BM juice at a dose of 0.75% or higher (P < 0.05). At the highest dose, BM-supplemented rats had lower energy efficiency (P < 0.05) and tended (P = 0.10) to have less visceral fat mass. In a subsequent experiment, rats habitually fed a HF diet either continued to consume the diet or were switched to a HF+BM, low fat (LF; 7%) or LF+BM diet for 7 wk. BM was added at 0.75%. Final body weight and visceral fat mass of the two last-mentioned groups were similar to those of rats fed a LF diet for the entire duration. Rats switched to the HF+BM diet gained less weight and had less visceral fat than those fed the HF diet (P < 0.05). The addition of BM did not change apparent fat absorption. BM supplementation to the HF diet improved insulin resistance, lowered serum insulin and leptin but raised serum free fatty acid concentration (P < 0.05). This study reveals for the first time that BM reduces adiposity in rats fed a HF diet. BM appears to have multiple influences on glucose and lipid metabolism that strongly counteract the untoward effects of a high fat diet.