Dietary fiber refers to fiber that is naturally present in plant foods. Functional fiber is isolated fiber that is added to foods or used as a supplement. Functional fiber's effects are real, but studies linking lower cancer risk with higher dietary fiber intake may partly reflect benefits of other nutrients and compounds in whole plant foods. Fiber is not all the same, and sources differ in the health benefits they offer. Here's a rundown on different fiber types:

Traditionally, fiber was classified as soluble (linked with lower blood cholesterol) or insoluble (linked with better intestinal regularity). While these terms are still seen in some studies, each includes types of fiber that act quite differently.

Viscous fiber is gel-forming in the intestines; fermentable fiber is the type that gut bacteria can ferment.

Resistant starch -- a significant portion of the starch in dried beans -- has traditionally not been counted as dietary fiber, yet it also is fermented by gut bacteria.

Fiber sources and types overlap. Soluble fiber can be fermentable, viscous or both. Insoluble fiber may or may not be fermentable. The same food, whether apples, dried beans or oatmeal, contains several types of fiber. So, get your fiber from a wide variety of sources to gain the full array of potential health benefits.

Fiber-boosting strategies

The best strategy is to meet or exceed fiber recommendations through a variety of naturally high-fiber foods so you get all types of fiber and the bevy of nutrients that accompany them. Expand your high-fiber choices from these categories daily:

Grains: Each 1/2 cup (or 1-ounce) serving of whole grains provides 2 to 4 g of dietary fiber; some with added bran provide 5 to 10 g.

--Grain products, including pita bread and sandwich wraps, labeled "contains whole grains" are better than refined grains, but not as good as "100 percent whole grain."

--If switching to a high-fiber cereal is challenging, mix it with your usual lower-fiber choice as you transition.

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