SAN DIEGO -- The grapefruit diet, which gained popularity in the '70s and then faded, is back.

Now, for the first time, there is scientific evidence that confirms grapefruit can promote weight loss.

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Study Claims Grapefruit Diet Works

For decades, the grapefruit has been a staple for dieters. The fruit has a powerful effect on the liver and the body. But until now, researchers did not know if it could really help with weight loss.

Nutritional researcher Ken Fujioka at Scripps Research Institute in La Jolla, Calif., led a study to find out whether grapefruit really possesses weight loss properties.

"We did not expect to see this kind of weight loss, in all honesty," Fujioka said.

Researchers believe there is a compound in grapefruit that interacts with the liver to lower cholesterol and helps regulate insulin. Too much insulin can cause weight gain.

"The fresh grapefruit actually lowered their insulin," Fujioka said.

The 12-week study found that people who ate fresh grapefruit or drank grapefruit juice lost weight without changing their diet.

"We took a group of people who had a half of a grapefruit three times a day before each meal. And, much to our surprise, without really altering their diet, they lost 3½ pounds, or a pound a week, without really doing anything else," Fujioka said.

Researchers said the weight loss has something to do with the grapefruit membrane.

"It may be that the membrane has something that will give you a feeling of fullness or it has separate effect in helping with weight loss. We are not really sure," Fujioka said.

But even those who drank grapefruit juice lost weight.

Now researchers want to see if this potent fruit will help people with metabolic disorders lose weight.

Grapefruit can cause problems with certain medications, so be sure to check with your doctor before starting this diet.

The study included 100 San Diego participants and was funded by a research grant from the state of Florida.

A larger study is planned for next year.