As part of a new study at the University of California, Berkeley, two groups of mice were fed a high-fat diet. One group was also given clarified, pulp-free grapefruit juice. The other drank water. At the end of the experiment, the juice-drinkers had put on 18 percent fewer pounds than the control group.
"I was surprised by the findings," study co-author Andreas Stahl, an associate professor of nutritional sciences and toxicology at UC Berkeley, said in a press release. "We even re-checked the calibration of our glucose sensors, and we got the same results over and over again."
The study was funded by the California Grapefruit Growers Cooperative, but researchers insist they and their study was uninfluenced by outside interests.
After finding that the juice-drinking mice also had lower blood glucose levels, the scientists decided to pit grapefruit juice against a glucose-lowering drug usually used to treat Type 2 diabetes.
"The grapefruit juice lowered blood glucose to the same degree as metformin," Stahl's colleague and study co-author, Joseph Napoli, said. "That means a natural fruit drink lowered glucose levels as effectively as a prescription drug."
Researchers also attempted to isolate the vital ingredient in grapefruit juice by giving mice naringin, a grapefruit component previously linked to weight loss, but found it didn't hold up under the scrutiny of lab experiments.
"There are many active compounds in grapefruit juice, and we don't always understand how all those compounds work," said Stahl. "Basically, we couldn't see a smoking gun that could explain why or how grapefruit juice affects weight gain."
Naturally, Stahl and his colleagues say they're not giving up yet; there is more testing to come. These latest experiments were detailed in the latest edition of the journal PLOS ONE.