Grapefruit juice can help dieters lose weight, and also assist in the management of diabetes, according to a new study from the University of California.

Mice were fed a high-fat diet, and provided with either water or grapefruit juice to drink. Those rodents who drank fruit juice gained significantly less weight than those who consumed water. In addition, both insulin and blood sugar levels were much healthier among those given the citrus beverage than the control group, promoting better protection against diabetes. Triglycerides, a type of fatty compound essential for the absorption of sugar into the bloodstream, were also better-maintained by mice who drank juice.

Blood glucose levels were down between 13 and 17 percent in mice given grapefruit juice, and insulin levels in the blood decreased by 66 percent. Weight gain was reduced an average of 18 percent through the intake of grapefruit juice among mice in the study.

Water provided to the control group of mice included glucose and artificial sweeteners, in order to match the saccharin content and calories of grapefruit juice.

Mice in the study were separated into six groups, some of which ate a high-fat diet, consuming meals of up to 60 percent fat, while others ate diets with fat levels as los as 10 percent. Researchers did not find as great of a difference among mice eating a low fat diet, as among those with high levels.

Grapefruit juice has long been a regular component of many popular diets, and many people swear by the weight-loss effects they have seen from consuming the beverage. This is the first study that shows this popularly-held belief is true, showing this natural substance is just as effective as metformin, a frequently-prescribed drug for diabetes, at treating the disease.

The Grapefruit Diet started becoming popular in the 1930's, and is sometimes called the Hollywood diet. The plan centers on reducing calories, while consuming grapefruit with every meal.

"I was surprised by the findings. We even re-checked the calibration of our glucose sensors, and we got the same results over and over again," Andreas Stahl, associate professor of nutritional sciences and toxicology at the University of California Berkeley, said.

Researchers are uncertain how or why the fruit juice helps to control diabetes, or assists with weight loss. Human trials still need to be conducted, to measure whether or not the fruit has an effect on obesity and diabetes in our species.

This investigation was funded by the California Grapefruit Growers Cooperative, but researchers insist this did not affect or bias the study in any way.

Research into the role grapefruit juice can play in management of diabetes and weight loss was profiled in the online journal Plos One.