The beneficial health effects of dietary fiber have long been a controversial issue in the health care community, as well as the dietary supplement industry. This has, at least in part, been the result of some premature and, to a lesser extent, unscrupulous claims about the benefits of fiber in the human diet. As in all matters involving medical research, it has taken some time to elucidate and substantiate the true nutritional benefits of fiber as well as its role in preventive health.
      In May 2001, the prestigious National Academy of Sciences (NAS) released a comprehensive report on fiber, a component of their multi-year study on Dietary Reference Intakes. Dietary Reference Intakes: Proposed Definition of Dietary Fiber serves as a preliminary report that defines what fiber is, proposes a definition of terms, and summarizes its health benefits. The forthcoming complementary NAS study on the dietary reference intakes for the macronutrients (as yet untitled) will quantify the recommended amount of fiber in the diet. It is scheduled for completion later this year.

      The National Academy of Sciences has been evaluating the science of human nutrition for decades, the results of which have been used by the Food and Drug Administration (FDA) as the basis for food labeling in the U.S. It is not unreasonable to conclude that the current NAS summary on the definition and health benefits of fiber, as well as their forthcoming quantitative recommendations for dietary intake of fiber, will subsequently become the basis of the recommended intake of fiber on food labels in this country.
      It is also reasonable to conclude that the recommended amount of fiber that should be included in the daily human diet will be considerably higher than most individuals will consume, or can reasonably be expected to consume, based upon the average adult diet. This fact has not been lost on dietary supplement manufacturers, and is the driving force behind the proliferation of the marketing of dietary fiber supplements.

      The NAS report details, at some length, the biochemical definition of fiber and its role in the human diet. In summary, the report proposes a new definition of dietary fiber:       The report goes on to recommend the gradual phasing out of the currently used terms, insoluble fiber and soluble fiber, and replacing them with dietary fiber and added fiber, as the former are definitions based upon the analytical methods used to quantify fiber, while the latter are based upon physiologic function and its resulting health benefit.
      Dietary Fiber includes food plant carbohydrates, consisting primarily of material derived from the plant cell wall or its intercellular structure, that is essentially nondigestible in the human small intestine, and is further distinguished by the presence of other macronutrients, such as digestible carbohydrates and protein. A few examples would include cereals, such as ground brans and flaked corn, legumes, onions, some artichokes, as well as many other fruits and vegetables.
      Added Fiber is specific to fiber with known beneficial effects in humans, and is characterized by nondigestible carbohydrates that are not integral to food plant structure; i.e., extracted by enzymatic, aqueous or other chemical processing, and synthetically manufactured or naturally occurring isolated oligosaccharides and manufactured resistant starch. This group also includes animal-derived nondigestible carbohydrates. By definition, intact and unprocessed food sources contain only small quantities of added fiber, larger concentrations being available only in special preparations such as those found in dietary supplements.
      On the matter of the redefinition of terms, the NAS report concludes that... “these definitions are a true improvement over existing definitions because they begin to recognize fiber as a nutrient with demonstrable health effects and lessen the emphasis on fiber as a constituent of food requiring quantification; this improvement warrants the adaptation that will have to occur... in developments and modifications of fiber analysis, additional research into physiological actions of many fibers... and the reflection of these efforts on food composition databases and on the nutrient label.”

      Among the conclusions of this important report are a number of observations that have been publicized by the dietary supplement industry for a number of years, based upon the same research evaluated by the NAS study: Simply put, dietary fiber contributes to the reduction of high blood sugar, contributes to the reduction of high cholesterol, and promotes bowel evacuation by acting as a mild laxative which can result in any number of preventive health benefits.