Contrasting effects of non-starch polysaccharide and resistant starch-based diets on the disposition and excretion of the food carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in a rat model Lynnette R. Ferguson a,b, *, Shuotun Zhu b , Philip Kestell b a Discipline of Nutrition, University of Auckland Faculty of Medicine and Health Science, Private Bag 92019, Auckland, New Zealand b Auckland Cancer Society Research Centre, University of Auckland Faculty of Medicine and Health Science, Private Bag 92019, Auckland, New Zealand Accepted 17 January 2003 Abstract It has commonly been believed that increasing fibre in the diet should reduce the incidence of cancers, especially those of the colon and rectum. The earliest definitions of dietary fibre restricted the term to plant cell walls in which non-starch polysaccharides are key chemical components. However, new definitions encompass a wider range of materials, including starches resistant to digestion in the colon (resistant starches). Nevertheless, most definitions require that ‘‘dietary fibres’’ show physiological effects considered beneficial against cancer, including enhanced laxation and faecal bulking. On theoretical grounds, such properties might be expected to dilute the concentration of any carcinogen present and move it more rapidly through the colon, thereby reducing bioavailability. We have compared the properties of two dietary fibre preparations that are primarily non-starch polysaccharides with two resistant starch preparations for effects on carcinogen disposition in a rodent model. Although both preparations enhanced laxation and faecal bulking, only the non-starch polysaccharide preparation reduced carcinogen biovailability. Indeed, carcinogen biovailability was significantly enhanced by resistant starch. We suggest that there may be fundamental differences in the manner by which non-starch polysaccharides or resistant starches affect carcinogen disposition, and express concern that the events seen with the resistant starches [RS] are unlikely to be beneficial with respect to protection against cancer by exogenous carcinogens. Furthermore, the data reveal that the observation of enhanced laxation and faecal bulking does not necessarily imply a reduction in carcinogen bioavailability. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Dietary fibre; Resistant starch; Non starch polysaccharides; Carcinogen absorption; 2-Amino-3-methylimidazo[4,5-f]quinoline 1. Introduction A diet high in dietary fibre (DF) has been suggested to protect against various western diseases including colo- rectal cancer (Burkitt, 1971), and current nutrition guide- lines for many western countries recommend the intake of between 20–30 g of DF per day. This can theoretically be achieved by increasing levels of fruit, vegetables and/or cereal products (such as wheat bran) in the diet. The chemical component that has been considered impor- tant is non-starch polysaccharides (NSP), and indeed isolated NSP have been considered as a DF for many years (Harris and Ferguson, 1993; Englyst et al., 1992). Such materials as wheat bran are good DF sources, but it would be necessary to add around 25 g/day of wheat bran in order to add an extra 10 g of DF (Ferguson et al., 1997). Such quantities seem to be too high to be palatable to many people, so are not currently being reached. More recent definitions of DF (Baghurst et al., 1996; Prosky, 1999) have included forms of starch that are resistant to digestion in the colon (resistant starches or RS), and these appear to be more readily acceptable 0278-6915/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0278-6915(03)00012-7 Food and Chemical Toxicology 41 (2003) 785–792 www.elsevier.com/locate/foodchemtox Abbreviations: DF, dietary fibre; RS, resistant starch; NSP, non starch polysaccharides; IQ, 2-amino-3-methylimidazo[4,5-f]quinoline. * Corresponding author. Tel.: +64-9-373-7599x86372; fax: +64-9- 373-7502. E-mail address: l.ferguson@auckland.ac.nz (L.R. Ferguson).