What is Fiber? 

New Definitions

There are two main ways that scientists define fiber, analytically and physiologically. Analytical methods dissect foods, to arrive at “fiber content” for labeling purposes; they define “fiber” as any food component that reacts a certain way during the dissection process in a chemical lab. Physiological methods define fiber as any food component that reacts a certain way during the digestive process in our bodies.

Some food components test positive as fiber through both these methods, while others with proven beneficial digestive and physiological effects aren’t measurable through traditional analytical methods. This dichotomy has led to efforts to create new, more comprehensive analysis procedures – and new definitions of fiber.

Since 1953, when nutritionist EH Hipley first coined the term “dietary fiber,” the scientific community has struggled to define the meaning of this phrase. Most recently, in 2000, the American Association of Cereal Chemists (AACC) proposed a physiological definition that would include many components not traditionally considered fiber according to analytical methods.  Two years later, the National Academy of Sciences built on the work of the AACC and many other sources to create its own updated definition.

DEFINITION OF FIBER

American Association of Cereal Chemists (2000)

Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation.

DEFINITION OF FIBER

National Academy of Sciences (2002)

Dietary Fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants.

Functional Fiber consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humans.

Total Fiber is the sum of Dietary Fiber and Functional Fiber.

The NAS definition recognizes the many natural sources of fiber as Dietary Fiber, and classifies most manufactured fibers as Functional Fiber.  Naturally occurring resistant starch (such as found in whole grains, legumes, cooked and chilled pasta, potatoes and rice, unripe bananas) is considered Dietary Fiber under the NAS definition; Resistant starches added to foods for health benefits are classified as Functional Fiber.