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Food & Beverage Industry

Redefining

Prepared Foods, Feb, 2000 by Linda Milo Ohr

A new proposal broadens the definition of dietary fiber.

Some may argue whether to spell it "fiber" or "fibre," but food scientists, nutritionists and academics are currently wrestling with a much more important question: the definition of fiber itself.

An expert ad hoc committee created by the American Assoc. of Cereal Chemists (AACC) is currently drafting a new definition of dietary fiber. The draft takes into account some of fiber's physiological effects and broadens the definition to include polyfructans and oligosaccharides. If the FDA were to base fiber policy on the new definition, these ingredients could be labeled as dietary fiber in final food products.

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The committee will issue its draft along with a final report to AACC's board of directors in February 2000, says Bryan Tungland, an active participant in AACC's ongoing dietary fiber discussion and vice president of scientific and regulatory affairs for an inulin supplier.

Upon receipt and approval of the report, AACC will make the new definition for dietary fiber available for all regulatory bodies throughout the world to use at their discretion.

According to Tungland, the definition being submitted to the board of directors will define dietary fiber as being made up of edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine. The proposed definition would also include dietary components not currently part of the dietary fiber complex, such as polyfructans and oligosaccharides. Another key element of the proposed definition/description will likely be a statement of fiber's beneficial physiological effects, such as laxation, blood glucose attenuation and/or blood cholesterol attenuation.

A Physiological Perspective

Some may wonder why a new definition of dietary fiber is necessary. The current de facto definition of dietary fiber reads, "Dietary fiber consists of the remnants of edible plant cells, polysaccharides, lignin and associated substances resistant to (hydrolysis) digestion by the alimentary enzymes of humans."

The current FDA-approved method of measuring total dietary fiber for nutrition labeling--method 985.29 by the Assoc. of Official Analytical Chemists (AOAC)--accurately measures those substances listed in this de facto definition.

"The brief description of this method serves as the current definition of dietary fiber. Dietary fiber is the defatted food material that remains after in vitro digestion with two amylases and one protease to simulate physiological digestion, and it precipitates in 78% alcohol, corrected for protein and ash in the precipitate," said Dennis Gordon, chair of the AACC Dietary Fiber committee in Cereal Foods World, Feb. 1999.

This analytical definition doesn't take into account any of fiber's physiological properties, even though physiological properties are what make fiber beneficial to human health.

Consumption of both insoluble and soluble fiber results in distinct physiological effects. Insoluble dietary fiber is relatively unfermentable in the colon and has a high water-holding capacity, which results in the formation of softer stools that pass through the system faster. Shorter transit time reduces exposure of the gut walls to cytotoxic and carcinogenic compounds and thus lowers the risk of several gastrointestinal disorders, including enteritis, colitis, diverticulitis, colorectal cancer and other gastrointestinal disturbances. Softer stools also reduce constipation and ease or prevent hemorrhoids, explains Tungland. Another modest effect of insoluble fiber is its scrubbing/cleaning action on epithelial walls in the intestine.

In general, soluble fiber reduces calorie load to the host and adds viscosity, which has an effect on insulin resistance and postprandial blood sugar increase, says Tungland. A viscous soluble fiber slows transit of chyme in the upper gastrointestinal tract, resulting in slower absorption rates, lower blood concentrations of nutrients and altered hormonal responses to the absorbed nutrients. This affects cholesterol absorption.

"By contrast, low-viscosity soluble dietary fibers such as inulin have little effect on gastric emptying, but rather appear to affect blood glucose and cholesterol levels by regulating hepatic enzymes through the production of specific short-chain fatty acids," explains Tungland. "Scientific studies in animals suggest that short-chain fatty acids produced during inulin fermentation have influence on hepatic lipogenic enzymes and reduce hepatic fatty acid and triglyceride synthesis."

As soluble dietary fiber is fermented in the colon, a substantial quantity of soft, bulky and water-retaining bacterial mass accumulates. This increase in bacterial mass and stool softening affects transit time, providing relief of constipation.

Increased research of selective dietary fibers (prebiotics) such as inulin has cited additional physiological activities, including enhanced resorption of minerals such as calcium, magnesium and iron in the large intestine and promotion of the growth of beneficial gut microflora such as bifidobacteria. These health-promoting gut microflora inhibit growth of harmful bacteria and result in the synthesis of B vitamins and digestive enzymes; promote proper digestion and intestinal function; reduce food intolerances and allergies; produce immune-stimulating factors; and help reduce levels of carcinogenic compounds in the colon.

Food & Beverage Industry

Redefining

Prepared Foods, Feb, 2000 by Linda Milo Ohr

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