Is it true that grapefruit juice has more nutrients than other fruit juices?

Yes, according to a new study by researchers at the University of Florida Institute of Food and Agricultural Sciences. But read on, because grapefruit and grapefruit juice aren't risk free.

The study, led by nutritionist Gail Rampersaud, whose position is supported by the Florida Department of Citrus, looked at six formulas for computing the density of nutrients per calorie in seven types of juice: apple, grape, orange, pink grapefruit, white grapefruit, pineapple, and prune.

Pink grapefruit juice came out tops in the nutrients-per-calorie race according to five of the six formulas, said Rampersaud, with orange juice second, followed by white grapefruit. Among the nutrients prevalent in these citrus fruits are vitamin C, folate, thiamin, vitamin A, and potassium. The advantage of drinking grapefruit juice, as opposed to eating grapefruit, said Rampersaud, is that it is more convenient; on the other hand, eating the fruit provides more fiber.

But before you tank up on grapefruit or grapefruit juice, be careful. Chemicals called furanocoumarins in grapefruit interfere with an enzyme called CYP3A in the intestine whose job is to break down certain drugs.

The furanocoumarins inactivate this enzyme, which means that higher levels of certain drugs get into the bloodstream, said David Greenblatt, chairman of the department of pharmacology and experimental therapeutics at Tufts University School of Medicine.

There are no significant grapefruit-drug interactions with over-the-counter medications, said Bill McCloskey, executive director of the center for drug information and natural products at the Massachusetts College of Pharmacy and Health Sciences. But some prescription drugs may interact with the fruit.

Among them are antiseizures drugs such as Tegretol; an antianxiety drug, BuSpar; statins such as Zocor and Mevacor; the tranquilizer, Valium; and some calcium channel blockers for high blood pressure such Plendil.

JUDY FOREMAN

E-mail health questions to foreman@globe.com.