A study by UC Berkeley researchers published Wednesday concluded that mice fed a high-fat diet gained about 18 percent less weight when they drank grapefruit juice than those that drank water and were fed the same diet.
The research, which was published in the peer-reviewed scientific journal PLOS ONE, also indicated that mice that were fed grapefruit juice showed better metabolic variables, such as lowered blood glucose and insulin levels, in comparison to their water-drinking counterparts.
A lower insulin level, according to Joseph Napoli, one of the researchers and chair of the campus department of nutritional science and toxicology, indicates higher insulin sensitivity. When individuals have insulin insensitivity, they are more prone to develop type-two diabetes.
Grapefruit juice has been linked to weight loss in the past, and many “popularized Hollywood diets” promote juice consumption, according to Andreas Stahl, associate professor of nutritional sciences.
Together, Napoli and Stahl led the six-person research team.
“We set out with a very skeptical mind at the beginning,” Stahl said. “I thought that the juice would have no effect. The results were a surprise for me.”
Though there were previous experiments that involved animal tests and grapefruit juice, there was a “discordance in the literature,” leading to different conclusions, according to Napoli.
“We wanted to create a well controlled, animal-based paradigm to look at the effect of grapefruit juice,” Stahl said.
Funding for the research came from the California Grapefruit Growers Cooperative, which approached the researchers and proposed the idea.
“The grapefruit growers came to us, because grapefruit juice has gotten bad publicity,” Napoli said. “We told them that we can’t predict the outcome, and we can’t guarantee anything. But we did continue with preliminary tests.”
Mice were split into six groups and given either high- or low-fat diets. Members of each group were then given clarified grapefruit juice, sweetened water, water with naringin — a component of grapefruits — or metformin, an anti-diabetic drug.
The grapefruit juice was diluted with water, and saccharin was added to mask the juice’s bitter taste. The water groups had the same glucose and saccharin content to match the grapefruit juice.
Researchers discovered that only the mice given grapefruit juice during the diet experienced weight loss. The team, however, has not yet identified which component of the juice led to the weight loss.
“It’s certainly interesting,” said Daniel Nomura, an assistant professor in the nutritional science department. “Once you identify what the active chemical ingredient in the grapefruit juice is, you might be able to turn it into a therapeutic drug.”
Though the cooperative has ceased funding the experiments, Napoli hopes to expand the research by investigating the lowest possible amount of grapefruit juice needed to still be weight-loss effective. Further funding would be achieved through federal grants.
“Their findings stress the importance of rigorous research on nutrition and nutraceuticals in human health and disease,” said James Olzmann, an assistant professor in the nutrional science department, in an email. “The intersection of nutrition and disease remains an untapped area of study with a lot of potential to positively impact human health and medicine.”
According to Stahl, the team also hopes that its animal tests will spur other researchers to use the same parameters on human cohorts.
“We are an agricultural college,” Napoli said. “We have an obligation to the California growers. (The research) was done in good citizenship.”