A diet high in fat and meat but low in dietary fibre increases the genotoxic potential of 'faecal water'

To determine the effects of different diets on the genotoxicity of human fa ecal water, a diet rich in fat, meat and sugar but poor in vegetables and f ree of wholemeal products (diet 1) was consumed by seven healthy volunteers over a period of 12 days. One week after the end of this period, the volun teers started to consume a diet enriched with vegetables and wholemeal prod ucts but poor in fat and meat (diet 2) over a second period of 12 days. The genotoxic effect of faecal waters obtained after both diets was assessed w ith the single cell gel electrophoresis (Comet assay) using the human colon adenocarcinoma cell line HT29 clone 19a as a target. The fluorescence and length of the tails of the comet images reflects the degree of DNA damage i n single cells, The mean DNA damage, expressed as the ratio of tail intensi ty (fluorescence in the tail) to total intensity of the comet after incubat ion with faecal water from volunteers consuming diet 1 was about twice as h igh as for diet 2, The susceptibility of the cells incubated with faecal wa ter to DNA damage caused by additional hydrogen peroxide treatment showed n o significant differences between the two diets. Generation of oxidized pyr imidine and purine bases revealed no differences after pretreatment with bo th types of faecal water. The results indicate that diets high in fat and m eat but low in dietary fibre increase the genotoxicity of faecal water to c olonic cells and may contribute to an enhanced risk of colorectal cancer.