Resistant starches (RS) have been shown to have a wide variety of physiological benefits. Many of these positive effects arise from the fermentation of the RS by the colonic microflora. It has been observed that RS acts as a prebiotic by promoting the growth and beneficial activity of specific species of colonic bacteria while reducing the numbers of pathogenic microorganisms. The use of RS is effective in stimulating the indigenous microflora to assist in the treatment of conditions such as bacterially induced diarrhoea and ulcerative colitis. Although probiotics have often been linked with improving the health of the host, experimental results concerning their efficacy have been inconsistent. It has been suggested that "synbiotics", a combination of prebiotic and probiotic, would be useful in improving the reproducibility of the beneficial results obtained from Probiotics. RS offers the opportunity of providing "targeted synbiotics". In this case the RS has multiple functionalities through assisting in the protection of the viability of the probiotic during its passage through the upper gastrointestinal tract and then in helping to induce the desired specific physiological effect in the colon. The preparation of a targeted synbiotic, incorporating a Bifidobacteria lactis and a RS from high amylose maize that is specifically fermented by this bacterial strain, has been shown to significantly increase the apoptotic index (a positive biomarker) in a colorectal cancer rat model. The diversity of forms and types of RS offer the opportunity to prepare targeted synbiotics using selected probiotics to improve colonic health and/or treat various diseases that occur in the large bowel.

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The present review refers to the proposal for resolving the confusion on concept of dietary fiber in the world. The working committee established by Japanese Association for Dietary Fiber Research (JDF) in 1997 first overviewed the changes of discussions on the definition, terminology and classification of dietary fiber conducted in different countries since 1972. Further reviewing has been carried out concerning the physiological significance and classification of new indigestible substances appearing year by year with the proceedings of the researches in this field. Based on the discussions, the committee members agreed that the term "dietary fiber" is inappropriate as a term which covers all indigestible components. The "luminacoids" was designed, as a comprehensive term that covers all such components, including dietary fiber in the conventional meaning. This comprehensive terminology should be classified into starch and non-starch components. Dietary fiber is a major component of non-starch substances and can be sub-classified into polysaccharides and lignin. Thus, the definition of "luminacoids" is proposed as follows: "dietary components which are not digested and/or absorbed in the human small intestine and which exert physiological effect that are useful in maintaining good health via the gastrointestinal tract". After presenting the proposal to the Annual Meeting of JDF in 1998 and 1999, it was finally approved at the 6th Annual Meeting in November 2000. We further describe the significance of new proposal by JDF, and also compare and discuss about these advantages and drawbacks of each revised definition of dietary fiber proposed currently by five international organizations and other investigators.

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Effects of viscous dietary fibers on the digestive organs were investigated in 5 week aged rats. Rats were fed the diets containing cellulose, pectin, tamarind gum or sodium alginate at 4.78% as Prosky dietary fiber for 19 days. After feeding, weights of digestive organs and activities of digestive enzymes in the pancreas and small intestinal mucosa were determined. 1. The weight gains were lower in the groups fed viscous dietary fibers compared with cellulose group, significantly lower in sodium alginate group. 2. The weights of small intestine and cecum were significantly higher in the groups of viscous dietary fibers than the cellulose group. The stomach was significantly heavier in the sodium alginate group and colon was significantly heavier in the pectin and sodium alginate groups. 3. The protease activity in the pancreas was higher in the sodium alginate group compared with other groups. 4. Disaccharidase activities in the jejunal mucosa were lower in the groups of viscous dietary fibers than in the cellulose group, whereas the disaccharidase activities in the duodenal mucosa were similar among the groups. Our observations suggest that the viscosity of dietary fiber was associated with the enlargement of digestive organs and the increased enzyme activity in the pancreas. However, another mechanisms may play in the mucosal enzymes of small intestine.

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