Mice that were fed a high-fat diet gained 18 percent less weight when they drank grapefruit juice, a new study finds.

The study was conducted by researchers from the University of California - Berkeley. The researchers noted that this juice was more effective in keeping weight gain at bay when it was clarified and without pulp.

"I was surprised by the findings," said  Andreas Stahl, associate professor of nutritional sciences and toxicology, in a press statement. "We even re-checked the calibration of our glucose sensors, and we got the same results over and over again. We see all sorts of scams about nutrition. But these results, based on controlled experiments, warrant further study of the potential health-promoting properties of grapefruit juice."

The mice in the study were divided into six groups based on the liquid they consumed. The liquid groups included sweetened diluted grapefruit juice, sweetened water and water mixed with metformin. There was also a controlled group that drank only water. The mice were fed either a high-fat or a low-fat diet.

At the end of the study, researchers found that the mice who were given a high-fat diet and drank diluted grapefruit juice not only gained less weight than their control counterparts, they also had a 13 to 17 percent decrease in blood glucose levels and a threefold decrease in insulin levels, which reveals greater sensitivity to insulin.

"The grapefruit juice lowered blood glucose to the same degree as metformin," said Joseph Napoli, professor and chair of nutritional sciences and toxicology. "That means a natural fruit drink lowered glucose levels as effectively as a prescription drug."

The impact was not so great among the mice that were given the low-fat diet. Those that drank the juice experienced a two-fold decrease in insulin levels, but there was no significant change in weight or other metabolic variables.

"The effects were more subtle for the low-fat diet group," explained Stahl. "Mice are incredibly healthy animals with naturally low levels of bad cholesterol. So if they are eating a healthy, low-fat diet, it will take more to see a significant effect on their health."

"Basically, we couldn't see a smoking gun that could explain why or how grapefruit juice affects weight gain," said Stahl. "Obesity and insulin resistance are such huge problems in our society. These data provide impetus to carry out more studies."

The study was funded by the California Grapefruit Growers Cooperative. Findings of the research were published online in the journal PLOS ONE.