FROM ASN EB 2012 SYMPOSIA Dietary Fiber Future Directions

The CODEX Alimentarius definition of dietary fiber includes all nondigestible carbohydrate polymers with a degree of polymerization of 3 or more as dietary fiber with the proviso that they show health benefits. The global definition, if accepted by all authoritative bodies, offers a chance for international harmonization in research, food composition tables, and food labeling. Its nonacceptance highlights problems that may develop when definitions vary by region. The definition requires that the research community agrees upon physiological effects for which there is substantial scientific agreement, e.g., fibers’ effects on laxation and gut health, on attenuating blood lipids and blood glucose and insulin, and in promoting fermentation in the large bowel. The definition also necessitates the delineation of research protocols to prove the benefits of various isolated and synthesized fibers. These should emanate from evidence-based reviews that fairly weigh epidemiological data while considering that added fibers are not reflected in many food composition databases. They then should include well-controlled, randomized, control trials and utilize animal studies to determine mechanisms. Agreement on many study variables such as the type of subject and the type of baseline diet that best fits the question under investigation will also be needed. Finally, the definition establishes that all types of fiber can address the severe fiber consumption gap that exists throughout the world by recognizing that the combination of fiber-rich and -fortified foods increases fiber intake while allowing consumers to stay within allowed energy levels. Adv. Nutr. 4: 8–15, 2013. Introduction The realization nearly 50 y ago that dietary fiber is important to good health has resulted in a “holy grail” quest to have a definition that includes all the types of substances that fulfill the criteria set by the definition. Currently, existing definitions may fail to capture all the nondigestible material in food. Thus, the issuance by CODEX Alimentarius of an international definition of dietary fiber in 2009 marked an important step forward for fiber research and nutrition (see Appendix). A single worldwide definition enables research studies to be comparable, because all would include the same materials measured in the same way. The fact that the CODEX process took over 16 y is testament to the difficulty in reaching international consensus on the definition. The CODEX definition has been adopted or reaffirmed by many national authorities, but it did not completely solve the issue of international harmonization, because a footnote to the definition allows national authorities to choose whether or not to include nondigestible polymers that are shorter than 10 sugar units [degree of polymerization (DP) #10]. Thus, the DP issue could impair international harmonization if some countries decide not to accept these short chain oligomers as dietary fiber. This paper will review the CODEX definition and its acceptance in countries around the world. It will feature the 3 CODEX classifications of fiber. These include fibers in category 1 that are intrinsic and intact; in category 2 that are extracted from food materials by some physical, chemical, or mechanical means; and in category 3 that are synthesized 1 Presented at the symposium “Frontiers in Fiber Nutrition Research and Applications” held at the Experimental Biology 2012 meeting, April 23, 2012, in San Diego, CA. The symposium was sponsored by the American Society for Nutrition and supported in part by educational grants from Corn Products International and Kraft Foods, Inc. A summary of the symposium “Frontiers in Fiber Nutrition Research and Application” was published in the September 2012 issue of Advances in Nutrition. 2 Author disclosure: J.M. Jones is a scientific advisor for the International Life Sciences Institute and the Joint Institute of Food Safety and Nutrition of the U.S. FDA and University of Maryland, the Grains Food Foundation, and the Wheat Foods Council. She has received travel grants to deliver speeches at conventions and for manuscript support, served on advisory panels, and has received support for student and other projects in the past 5 y from the Beneo Institute, California Raisin Marketing Board, the California Fig Advisory Board, Calorie Control Council, the Campbell Soup Company, the Traditional Dried Fruit Coalition, the Wine Grape Institute, Dakota Communities for the Developmentally Disabled, GMI Inc., EU’s HealthGrain Coalition, and WK Kellogg. * To whom correspondence should be addressed. E-mail: jmjones@stkate.edu. 8 ã2013 American Society for Nutrition. Adv. Nutr. 4: 8–15, 2013; doi:10.3945/an.112. 002907. Downloaded from https://academic.oup. com/advances/article-abstract/4/1/8/4591588 by guest on 30 March 2018 or modified. Fibers in categories 2 and 3 require proof of their physiological benefits and data supporting this must show substantial scientific agreement. Research protocols are needed that will enable the approval of fibers from categories 2 and 3. Such protocols will likely require thorough characterization of the fiber in question and evidence-based reviews (EBRs) of existing data collating and synthesizing the existing literature regarding a particular isolated or synthesized fiber. Such reviews can help identify data gaps to set the direction for future fiber research. Further, research will be needed that not only clarifies the importance of adequate total dietary fiber intakes but also delineates the benefits and synergies that result from the intake of fibers of a variety of types and from a variety of sources. This review will try to outline some of the issues associated with each of these goals. Current status of knowledge Dietary fiber became an important nutritional concept in that late 1960s and early 1970s with the launching of the dietary fiber hypothesis by a team of British physicians, Burkitt, Painter, Walker, and Trowell (1–3). They noted that diseases regularly seen in Western countries were rare in rural Africa. It was their contention that the difference in disease rates was due to differences in diet, specifically the marked difference in intake of unrefined carbohydrate. Thus, the dietary fiber hypothesis emerged. It suggested that the occurrence of conditions from constipation to coronary disease (Table 1) could be reduced with the addition of dietary fiber to the diet (1–3). With dietary fiber as part of the nutrition canon, advances in research and understanding of the kinds of materials and the many physiological benefits suggested a need to refine the definition of dietary fiber and to improve the methods required to measure it. The progression of existing dietary fiber definitions shows nuanced refinements in the definition. These definitions are found in the following references (4–14). The difficulty in arriving at a definition is due to many factors, but 3 important ones are: 1) the inability to define dietary fiber as a single chemical entity or group of chemically related compounds; 2) the many and varied physiological functions it performs; and 3) analytical difficulties in accurately characterizing it (13). In many ways, the discovery period for dietary fiber mirrors the discovery of vitamins and their functions. Both fibers and vitamins are heterogeneous groups of compounds. Both have unique and overlapping functions and their roles in improving nutrition and importance to health are without dispute. As with vitamins, health is optimal when all the various fiber entities are ingested in the recommended amounts so that they can complement and augment each other. Dietary fiber, as defined by all existing definitions, is recognized to be a group of carbohydrate polymers and oligomers that escape digestion in the small intestine and pass into the large bowel, where they are partially or completely fermented by the colonic microflora. Many definitions recognize that dietary fibers can be intrinsic in foods, extracted from edible material, synthesized, or modified and added back to the food or the diet. The 2009 CODEX (4) dietary fiber definition and the recently approved definition by Health Canada (5) both recognize this. The Institute of Medicine definition proposed in 2002 bears similarity with and differences from the CODEX definition (9). It is similar to the definition in that it recognizes carbohydrates that are not digested in the small intestine. It is different in that the CODEX definition enfranchises all materials, intrinsic or added, that have been proven to function physiologically as dietary fibers. The Institute of Medicine definition gives them different names: dietary fiber, functional fiber, and total fiber. This creates a scenario that reserves the term dietary fiber to be used only for those fibers that are intrinsic and intact. For some, this nuanced difference in naming appears to make functional fiber unqualified to be called dietary fiber and in fact suggests that it is fake fiber. This is an ironic conclusion, because there are much more intervention data on the benefits of isolated fibers than there are on fibers found in foods. Epidemiological data dominate the evidence proving the benefits of fibers inherent in foods. The difficulty with these data is attributing the beneficial effect to the fiber and not to other aspects of fiber-containing foods such as fruits and vegetables or whole grains. Dietary fiber, like other nutrients, only warrants interest from nutritionists and health professionals because of its physiological benefits. Nearly all dietary fiber definitions that include materials extracted from foods or those that are synthesized or modified and then added back to food require proof of at least one health benefit in order to attain the status of dietary fibers. While the metabolic fate of a dietary fiber does not differ by its origin as inherent in the food or added to the di