This paper summarizes the contradictory epidemiological data concerning the association between vegetal fibres intake and colorectal cancer incidence. The key to these discrepancies might reside in the different amounts and ratios of butyrate and other short chain fatty acids (SCFA) produced by colonic anaerobic bacteria during fermentation of fibers from different origins, wheat bran fibers being better producers and therefore more protective. Butyrate, an established histone deacetylase inhibitor, acts by favoring an active chromatin configuration of the P21WAF1/CIP1 gene which, as an inhibitor of cyclin-dependent protein-kinases, blocks the cell cycle.