Collaborative Study of a Method for Soluble and Insoluble Dietary Fiber

Abstract

The Food and Drug Administration issued a final rule in 1987 concerning the nutrition labeling of foods with respect to calories content¹. The Agency amended the existing food labeling regulations to provide for the exclusion of nondigestible dietary fiber when the calorie content of a food for nutrition labeling purposes is determined. In essence, the amendment allows a manufacturer to subtract the carbohydrate attributable to nondigestible fiber from the total carbohydrate content of a food, when the appropriate declaration of calorie content for that food is calculated. The Federal Register further stated that “The nondigestible dietary fiber will be determined by the method, Total Dietary Fiber in Foods, Enzymatic Gravimetric Method, First Action, in the Journal of the Association of Official Analytical Chemists (JAOAC), 68:399, 1985, as amended in JAOAC 69:370, 1986.” These methods were previously published as research papers previously in the JAOAC^2,3. Considering that soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) often exhibit distinctly different physiological effects⁴, the basic method was extended to give not only total dietary fiber (TDF) values, but also separate values for SDF and IDF. A previously completed interlaboratory study of a method for SDF and IDF⁵ revealed that the same enzymatic-gravimetric approach accepted by the AOAC for TDF could be used for SDF and IDF. The collaborative study reported on in this chapter is not yet completed, but sufficient data to assess its value as a method for determining SDF and IDF in a variety of foods and food products have been obtained.