Just the grapefruit facts.

Slice open a succulent grapefruit or pour yourself a glass of chilled grapefruit juice this winter and you'll be getting more than just a pucker and some vitamin C.

FIBER

All fruit contains fiber. An orange will give you seven grams, an apple five, and a banana four. But half a grapefruit provides six grams. That's about a quarter of the amount health authorities recommend. As with most fruits, roughly half of grapefruit's fiber is insoluble (which helps prevent constipation and which may reduce the risk of colon cancer) and half is soluble (which helps lower cholesterol levels).

There's a catch, though. To get all that fiber you have to eat the walls that separate the segments (It's okay to skip the stringy white stuff that's attached to the inside of the rind). That means peeling and eating your grapefruit like an orange, or digging out the walls with your spoon.

Don't like the chewy walls? You'll still get about two grams of fiber from spooning out the flesh from half a grapefruit. Grapefruit juice has no fiber. "Grapefruit can increase remarkably the absorption of certain drugs," says Paul Watkins, director of the University of Michigan's General Clinical Research Center in Ann Arbor.

In 1991, pharmacologist David Bailey of the University of Western Ontario reported that grapefruit juice boosted the average absorption of a blood pressure medication three-fold.(1)

Why? "There's an enzyme located along the gastrointestinal tract that partly inactivates certain drugs as they're being absorbed," says Watkins.

"Something in grapefruit juice neutralizes the enzyme, allowing more of those drugs than usual to be absorbed."

Although the risk of harm from this extra absorption is probably very low", says Bailey, "there's a potential for some people to experience side effects from their drugs because of it."

Among the drugs that grapefruit is known to affect: calcium-channel blockers like Procardia or Adalat, antihistamines like Seldane, immunosuppressants like cyclosporine, short-acting sedatives like Halcion, and estrogens like Estinyl.

So should you swear off grapefruit or grapefruit juice if you take them?

"Don't change your habits," says Watkins. "If you don't take your medicine with grapefruit juice in the morning, don't start. Doing that may interfere with the effective dosage your physician has determined."

The only exception: Invirase (saquinavir), a protease inhibitor taken by some people with HIV, is so poorly absorbed that using grapefruit juice to boost its effect can only help.

GOOD FOR THE HEART

"Do it for your heart," say the television ads for Florida grapefruit. "The American Heart Association (AHA) has certified Florida grapefruit and grapefruit juice as part of a heart-healthy diet."

What's Florida grapefruit got to do with your heart?

"Grapefruit and grapefruit juice are low in fat, saturated fat, and cholesterol," says Antigoni Pappas, manager of consumer nutrition for the AHA. "So they're foods that, when included in a low-fat balanced eating plan, can help to lower the risk of heart disease."

Of course, that's also true of many other fruits and vegetables. What's different about Florida grapefruit?

Its deep pockets. Florida farmers paid the Heart Association $450,000 for the exclusive right -- among U.S. grapefruit growers -- to promote its certification in their ads this season.

Grapefruit is a great fruit...but most unadvertised produce will make your heart just as happy.

(1) Lancet 337:268,1991