In the 70s, fiber was simply described as the remnants of plant cell wall components that are resistant to breakdown by human digestive enzymes. The definition was then broadened to include all digestion-resistant polysaccharides. Methods were developed first for total fiber, then insoluble and soluble fiber. As of 1999, the definition of dietary fiber remained as “dietary fiber consists of the remnants of edible plant cells, polysaccharides, lignin and associated substances resistant to (hydrolysis) digestion by the alimentary enzymes of humans.” This definition identifies a macro-constituent of foods that include cellulose, hemicellulose, lignin, gums, modified celluloses, mucilages, oligosaccharides, and pectins and associated minor substances, such as waxes, cutin, and suberin. (DeVries JW, et al. 1999, Cereal Foods World 44(5):367)
But today, as the physiological effects of dietary fiber become better understood via the proliferation of clinical studies, and as ingredient manufacturers devise new offerings that provide functional benefits in both food systems and human digestion, debate rages as to whether fiber should be defined by its source material, its chemistry or its human physiological effect. For example, many new carbohydrates that do not have fiber labeling status, such as inulin and several naturally based oligosaccharides, still meet the general definition or concept of dietary fiber. (See www.AACCnet.org discussion page.) Formulators who are confused about fiber functionality, label and regulatory status and nutritional implications are not alone. The chart “Fiber Labeling by Analysis” clarifies the measurement issue, as dietary fiber labeling status is determined by measurement methods based on solubility in 78% ethanol.