Fiber

(The Food and Drug Administration allows heart disease health claims for oats, barley, and psyllium, the fiber found in Metamucil.)

Perhaps it's because fiber lowers levels of "bad" LDL cholesterol, improves blood glucose levels, reduces inflammation, and binds to potential cancer-causing agents, helping to flush them out of the body, says lead author Yikyung Park, a staff scientist at the National Cancer Institute.

Inulin occurs naturally in chicory root and other plants and grains and is a form of soluble fiber but, like resistant starches, doesn't have the same anticholesterol effects, says Slavin.

Yogurts with added fiber actually contain inulin, a group of simple sugars that are not digested.

Because insoluble fiber hustles things along in the digestive tract, it's also a good source of relief if you're constipated.

Yogurts with added fiber actually contain inulin, a group of simple sugars that are not digested.

"Whole grains are rich sources of fiber, but also good sources of vitamins, minerals, and other phytochemicals that may provide health benefits," Park says.

Perhaps it's because fiber lowers levels of "bad" LDL cholesterol, improves blood glucose levels, reduces inflammation, and binds to potential cancer-causing agents, helping to flush them out of the body, says lead author Yikyung Park, a staff scientist at the National Cancer Institute.

So while there's an ongoing debate over which types of fiber confer which heart-protective benefits, the take-home is that no one should rely solely on soluble fibers to get the maximal heart benefit.

Here's a field guide to fiber sources:

Soluble fiber: Foods high in soluble fiber, so called because of its ability to dissolve readily in liquids—include oat bran, oatmeal, beans, peas, rice bran, barley, citrus fruits, strawberries, and apple pulp, according to the American Heart Association.

Unlike soluble fiber, it doesn't dissolve in liquids or form a gel but instead passes through the digestive tract pretty much unchanged.

They're found in legumes as well as starches like potatoes, pasta, and rice that have been cooked and cooled (as in potato or pasta salad, or sushi), and barely ripe bananas.

Men were 24 to 56 percent and women 34 to 59 percent less likely to die of heart and infectious or respiratory diseases, according to findings from the National Institutes of Health's AARP Diet and Health Study, published today in the Archives of Internal Medicine.

[Slide Show: 10 Fiber-Friendly Food Swaps]

Clearly, "all fibers are not created equal," cautions James Anderson, an endocrinologist at the University of Kentucky-Lexington.

Men were 24 to 56 percent and women 34 to 59 percent less likely to die of heart and infectious or respiratory diseases, according to findings from the National Institutes of Health's AARP Diet and Health Study, published today in the Archives of Internal Medicine.

And grains have powerful antioxidant and anti-inflammatory properties—another reason researchers say grain fiber is beneficial.

Viscous fibers found in foods like oat bran and beans seem to work particularly well because they form a gel in the gut that slows down fat formation and absorption, says Joanne Slavin, a professor of food science and nutrition at the University of Minnesota and author of the American Dietetic Association's 2008 position paper on dietary fiber.

Viscous fibers found in foods like oat bran and beans seem to work particularly well because they form a gel in the gut that slows down fat formation and absorption, says Joanne Slavin, a professor of food science and nutrition at the University of Minnesota and author of the American Dietetic Association's 2008 position paper on dietary fiber.

And they're also being added to foods to increase fiber content without affecting taste, as well as to reduce caloric density; a product called Hi-maize, for example, is added to pastas and energy bars.