Dietary fibres may protect or enhance carcinogenesis

Dietary fibre (DF) is widely considered to protect against cancer, especial ly colorectal cancer. However, a large prospective epidemiological study ha s shown no apparent effect of DF intake on the development of colorectal ca ncer. We suggest that this may be because the term DF represents a wide ran ge of materials, some able to protect, but some able to enhance carcinogene sis. This is consistent with data from animal carcinogenesis experiments. M ost of the DF in western diets is in the form of plant cell walls, but thes e vary in their composition and it is unlikely that all types are protectiv e. The few data available indicate that plant cell walls containing suberin or Lignin may be the most protective, although they are present in only sm all amounts in food plants. DFs are also added to foods. These include comp onents obtained from plant cell walls, such as pectins, as well as soluble DFs from other sources. In general, animal carcinogenesis experiments indic ate that soluble DFs do not protect and some may enhance carcinogenesis. Fe w human intervention studies have been done on DF or sources of DF, with th e exception of wheat bran, a good source of DF, which has been shown to pro tect. Possible mechanisms whereby DF may enhance carcinogenesis are discuss ed. In addition to DFs, resistant starches and non-digestible oligosacchari des are added to foods; these, like DF, escape digestion in the small intes tine. However, so far only a few animal carcinogenesis experiments have bee n reported using these materials, and no human intervention studies. We bel ieve caution should be exercised in the addition of such materials to food. (C) 1999 Elsevier Science B.V. All rights reserved.