To three groups of rats with medically induced diabetes, Ojieh and his colleagues gave metformin and varying doses of onion extract--200, 400 and 600 milligrams per kilograms of body weight daily (mg/kg/day)--to see if it would enhance the drug's effects. They also gave metformin and onion extract to three groups of nondiabetic rats with normal blood sugar, for comparison. Two control groups, one nondiabetic and one diabetic, received neither metformin nor onion extract. Another two groups (one with diabetes, one without) received only metformin and no onion extract. Each group contained five rats.
Two doses of onion extract, 400 and 600 mg/kg/day, strongly reduced fasting blood sugar levels in diabetic rats by 50 percent and 35 percent, respectively, compared with "baseline" levels at the start of the study before the rodents received onion extract, Ojieh reported.
Allium cepa also reportedly lowered the total cholesterol level in diabetic rats, with the two larger doses again having the greatest effects.
Onion extract led to an increase in average weight among nondiabetic rats but not diabetic rats.
"Onion is not high in calories," Ojieh said. "However, it seems to increase the metabolic rate and, with that, to increase the appetite, leading to an increase in feeding."
