Dietary Fiber- A Simple Matter?

Despite an evolving trend toward healthier eating, individuals continue to consume significantly less dietary fiber than the daily value (DV) of 25 or 30 grams, averaging only 14-15 g/person/ day. A recent study indicates only 24.4% of U.S. adults consumed fruits and vegetables (a good source of dietary fiber) five or more times per day (JAMA 286:1195, 2001).

Chronic inadequate intake of dietary fiber has led manufacturers to supplementing food with fiber and the marketing of dietary fiber supplements. As interest has increased in fiber and its potentially beneficial effects, manufactures have isolated dietary fiber for addition to food from a wide range of carbohydrate sources. Many of these isolated materials are used as food ingredients based on technical properties, such as thickening or fat reduction with fructans.

While the public and health experts are focused on the importance of dietary fiber and recommendations are made regarding intake, there has not been a consensus as to the definition of dietary fiber. Since the 1950s, a variety of definitions for dietary fiber have been promulgated by scientific and regulatory agencies worldwide. Some definitions specifically address the physiological effects of dietary fiber, whereas others rely more on prescribed analytical methods as the sole determinant of dietary fiber. Several analytical methods for the measurement of dietary fiber have been developed by the Association of Official Analytical Chemists International (AOAC) and are widely accepted in the U.S. In 1987, the FDA adopted the AOAC method 985.29 for regulatory purposes to identify dietary fiber as a mixture of non-starch polysaccharides, lignin and some resistant starch (resistant to the enzymes protease, amylase and amyloglucosidase used in the AOAC methods), with related methods added over the years. Therefore, the regulatory definition of dietary fiber is based on labeling and has been limited to methodology – the fiber must be enzymatically non-digestible and insoluble in four parts ethanol and one part water. This method excludes non-digestible water-soluble oligo- and polysaccharides, including polydextrose and fructans. At present, FDA does not have a written definition of dietary fiber for the purpose of food labeling and health claims.

The scientific community agrees the definition of dietary fiber should not only reflect methodology, but physiological effects as well. A commission of the Food and Nutrition Board’s (FNB)/Institute of Medicine (IOM) Dietary Reference Intake (DRI) Standing Committee established the Panel on the Definition of Dietary Fiber. The proposed definitions are included in the Institut