Fiber in ice cream? You read that right. It turns out that the hot new additive being showcased at your supermarket is good, old-fashioned fiber. Today, yogurt, instant breakfast drinks and even toaster pastries are being pumped with it. What's new about roughage? Recent research reveals it does a whole lot more than keep you regular: It may prevent many of the diseases of old age.

Fiber is naturally found in plant foods such as fruits, veggies, beans and whole grains. Your digestive system can't break fiber down, so it goes in one end and comes right out the other. But in between, it's powerful stuff. Trouble is, most of us only get about half the fiber we need - even with these manufacturers' additions. Here's why you need more:

IT KEEPS YOUR TICKER IN TIP TOP SHAPE

Foods like fruits, vegetables, steel-cut oats and beans sport a special kind of fiber known as soluble fiber (it dissolves in liquid) that lowers lousy LDL cholesterol. It does this by snatching up bile acids (molecules made from cholesterol that help you digest fat) in your gut, putting a handcuff on them and escorting them out of your body. Once those bile acids are history, your body has to rebuild its supply, so it steals cholesterol from your liver, lowering your LDL. In fact, people who got 10 grams of soluble fiber a day slashed their LDL by 5 percent.

IT MAKES YOUR GUT HAPPY

A different type of fiber - insoluble fiber - can fend off some not-too-pleasant digestive ills. Insoluble fiber, generally from foods containing wheat bran (bran cereal, whole-grain breads, whole-grain pastas) draws in water, keeping things going smoothly so your gut doesn't have to work too hard to help things along.

If your intestine has to strain to keep things moving, small pouches (diverticula) may form in its walls. These can become infected, resulting in a nasty condition known as diverticulitis. So preventing those pouches from developing in the first place is key.

But this isn't the only gut-friendly fiber. There are also prebiotics, fibers with funky names like inulin and fructooligosaccharides (try saying that 10 times fast!).

These guys supply nutrients to the good bacteria in your GI tract (called probiotics), helping them grow and multiply, so your gut stays healthy and is less susceptible to infection. Get prebiotics from foods including bananas, onions, garlic and artichokes.

IT WHITTLES DOWN YOUR WAIST

Fiber-filled foods are usually big on volume, yet low in calories.

Not only do they take a long time to chew, they slow down the rate at which food empties from your stomach. That means you feel full longer and eat less overall.

In fact, people ate 10 percent fewer calories when they replaced some of the low-fiber foods in their diets with foods supplying an extra 14 grams of fiber a day (the amount in a cup of cooked steel-cut oatmeal, two slices of whole-grain bread, an apple and a half cup of cooked broccoli).

So does all this mean you should run out and fill your freezer with fiber-enriched ice cream bars?

Sorry. Added fiber doesn't turn ice cream or a toaster pastry into anything as healthful as a juicy apple or a sweet beet.

Plus, fiber's biggest benefits come when it's naturally packaged in the form of whole foods, where you'll get a mix of different types of fiber.

(And there aren't recommendations for how much of which type of fiber you need, anyway. The best advice is to mix it up.) The plant foods that pack the fiber also bring you a bundle of age-defying vitamins, minerals and phytochemicals.

How much is right for you? Twenty-five grams a day if you're a woman or 35 grams if you're a man. But fiber up slowly.

Add about one serving of fiber-rich food to your life every week - unless you want to clear out every elevator you step into - and drink lots of water to help your digestive system adjust.

The You Docs - Mike Roizen and Mehmet Oz - are authors of the best-selling "You: The Owner's Manual" and "You: On a Diet." To submit questions and for more info, go to www.RealAge.com.