The onion extract used for the experiment in rats was a crude preparation from onion bulb.
“We need to investigate the mechanism by which onion brought about the blood glucose reduction,” said lead investigator Anthony Ojieh from the Delta State University in Abraka, Nigeria.
“We do not yet have an explanation,” Ojieh noted.
To rats with medically induced diabetes, the researchers 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.
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.
It 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. However, it seems to increase the metabolic rate and, with that, to increase the appetite, leading to an increase in feeding,” Ojieh said.
The findings were presented at ENDO 2015, the annual meeting of the Endocrine Society in San Diego, California.