WEDNESDAY, Aug. 25, 2004 (HealthDayNews) -- A grapefruit or two a day, along with a healthy diet, could help shrink widening waistlines. It might also cut smokers' risk for cancer as it inhibits a carcinogen in tobacco smoke.
Those findings come from two of several studies on the benefits of citrus fruits presented Wednesday at the annual meeting of the American Chemical Society in Philadelphia.
The so-called grapefruit diet -- which advocates mostly eating grapefruit with some protein -- has been popular on and off for weight loss for years, said Dr. Ken Fujioka, director of nutrition and metabolism research at the Scripps Clinic in San Diego and lead author of a study evaluating grapefruit for weight loss. Most nutrition experts have deemed the grapefruit-and-protein regimen unhealthy, and Fujioka is not advocating any return to such a strict diet.
However, his findings do suggest that a grapefruit or two each day, added to a balanced diet, might help the weight-conscious stay svelte.
In the study, Fujioka and his colleagues assigned 100 men and women who were obese to one of four groups. One group received grapefruit extract, another drank grapefruit juice with each meal, another ate half a grapefruit with each meal, while the fourth group received a placebo. "They weren't trying to diet," he said. "To make everyone even [on activity], all were asked to walk 30 minutes three times a week."
At the end of 12 weeks the placebo group lost on average just under half a pound, the extract group 2.4 pounds, the grapefruit juice group 3.3 pounds, and the fresh grapefruit group 3.5 pounds.
"In this study they had one and a half grapefruits a day," he noted. "That's not easy to do." And participants ate the fruit more like an orange: "They cut it in half, then into four sections, then separated the fruit from the skin." Eating grapefruit this way is thought to yield more beneficial compounds, he explained.
Exactly how grapefruit might spur weight loss isn't known, Fujioka said, but "it appears to help insulin resistance," which develops as people become obese.
The weight loss associated with eating grapefruit isn't surprising to another expert familiar with the study. "Eat fruit before any meal and you will lose weight," said Julie Upton, an American Dietetic Association spokeswoman. "The fiber fills you up, and fruit has fewer calories than other foods."
One half of a grapefruit has 60 calories, no fat, and six grams of fiber.
The fruit may have other health benefits. In a second study, grapefruit juice helped decrease the activity of an enzyme that makes cigarette smoke more carcinogenic.
Kristine Cuthrell, a research nutritionist at the University of Hawaii's Cancer Research Center, gave 49 smokers grapefruit juice or another test food, onions. Then they evaluated their urine to evaluate the activity of a liver enzyme called CYPIA2, thought to activate the cancer-causing chemicals found in tobacco smoke. Those who drank three six-ounce glasses of grapefruit juice a day reduced the activity of the enzyme, she said.
Other studies have also found that foods rich in flavonoids, like grapefruit, can inhibit the activation of a carcinogen, Cuthrell said.
The finding that grapefruit juice reduced the activity of the enzyme linked with making smoke more carcinogenic is also not surprising, Upton said, since a multitude of studies link eating a diet rich in fruits and vegetables with lowering cancer risk.
But she advised picking whole fruit over fruit juice whenever possible, because the whole fruit is more filling.
Cuthrell said, "My initial advice, of course, is to stop smoking. If you are not able to do that, it would not be a bad idea to drink a reasonable amount of grapefruit juice -- six to 12 ounces a day -- in addition to eating other fruits and vegetables." In the study, the grapefruit juice tested was white.
To learn more about grapefruit juice and its potential interaction with medications, visit the American Dietetic Association.