A Historical Perspective on Defining Dietary Fiber

It is generally believed that Hipsley in 1953 was the first to use “dietary fiber” as a shorthand term for the nondigestible constituents that make up the plant cell wall (1). These constituents were known to include cellulose, hemicellulose, and lignin. The term “dietary fiber” was clearly an attempt to distinguish some property or constituent of the food above and beyond what was then being measured by the crude fiber method. Between 1972 and 1976, Trowell, Burkitt, Walker, Painter, and co-workers (2‐6) adopted Hipsley’s term in conjunction with a number of health-related hypotheses they were developing, referred to as their “dietary fiber hypotheses. ” The term was used to describe the remnants of plant components that are resistant to hydrolysis by human alimentary enzymes. Thus it was a physiological-botanical description, characterizing dietary fiber’s indigestibility in the human small intestine, with plant cell walls being the major source of digestion-resistant material. The components included cellulose, hemicellulose, lignin, and associated minor substances, such as waxes, cutin, and suberin. Its edibility was implied. The inclusion of certain other obvious fiber properties was probably implied as well, such as those associated with the stringy fiber of celery and other vegetables and the character of edible peels on fruits, as well as the resistance of cereal bran to grinding. The “dietary fiber hypotheses” postulated an inverse relationship between dietary fiber consumption and the incidence of colon cancer and heart diseases. Publication of the hypotheses led to numerous dietary fiber research projects in nutrition, analysis, and food technology, among other areas. By 1976, the dietary fiber definition had been broadened to include all indigestible polysaccharides (mostly plant storage saccharides), such as gums, modified celluloses, mucilages, oligosaccharides, and pectins (7). It remained primarily a physiological definition, identifying dietary fiber on the basis of edibility and resistance to digestion, but was broadened to reflect chemical research findings obtained in the interim years. Some of the nondigestible polysaccharides were included because they were found to have the physiological actions attributed to dietary fiber but could not necessarily be chemically identified as having their origins in the cell wall. This broadened definition (6) quickly gained widespread acceptance. Driven by growing knowledge of the benefits of dietary fiber, numerous researchers began developing analytical methods in an attempt to quantify the portion of foods that provides the physiological functionality of dietary fiber. Among others, Asp of Sweden (8,9), Schweizer of Switzerland (10), Theander of Sweden (11,12,13), Southgate of the United Kingdom (14,15,16), and Furda, Baker, Van Soest, Heckman, and co-workers in the United States (17‐23) developed procedures aimed at achieving this goal. The focus was primarily on removing the digestible portions of the food from the digestion-resistant portions, using enzymes as the primary tool. Various degrees of success were achieved, but success was limited in part by digestive activity present in commercially available enzymes that was not present in human enzymes. In the late 1970s, Prosky began to seek consensus on a dietary fiber definition in the scientific community (24). To assist in the effort to quantify dietary fiber in foods for nutrition improvement and labeling purposes, he also sought consensus on analytical methodology that would be commensurate with the definition and gathered the opinions of over 100 scientists worldwide. By the 1981 spring workshop of the Association of Official Analytical Chemists (AOAC) in Ottawa, Canada, general consensus had been achieved (25) on pursuing methodology that would quantify dietary fiber, as defined by Trowell and co-workers in 1976. The methodological research work of Asp, Furda, and Schweizer and co-workers was deemed to be the best approach. In a cooperative effort led by Prosky, these researchers (along with DeVries and Harland) arrived at a single method deemed suitable for a multinational collaborative study. Interest in and support for this approach was so high that 43 laboratories in 29 countries agreed to participate in the study. After researcher’s initial disappointment with enzymatic-gravimetric methodology during a first collaborative study, minor modifications in the method protocol were made, a rugged accurate method was obtained, and a successful collaborative study was completed (26,27). The method was adopted by AOAC as the first Official Method of Analysis for total dietary fiber