Dietary habit affects the composition of human feces thus determining intestinal 
environment and exposure of colon mucosa to risk factors. Fecal water (FW) 
citotoxicity and genotoxicity were investigated in 33 healthy young Italian 
people, as well as the relationship between genotoxicity and nutrient intake or 
microflora composition. Two fecal samples were collected at 2 weeks apart and 
3-d dietary diary was recorded for each volunteer. Cytotoxicity was measured 
using the Trypan Blue Dye Exclusion assay and genotoxicity using the Comet Assay 
(alkaline single-cell electrophoresis). Fecal bifidobacteria, total microbial 
count and nutrient intakes were also assessed. High intra- and inter-variability 
in genotoxicity data and in bacteria counts were found. None of the FW samples 
were citotoxic, but 90% of FW samples were genotoxic. Seventy five percent 
indicated intermediate and 15% were highly genotoxic. There was a different 
sex-related distribution. Genotoxicity was positively correlated to the total 
lipid intake in females and to the bifidobacteria/total bacteria count ratio in 
male volunteers. These results demonstrate that the majority of FW samples 
isolated from free-living Italian people show intermediate level of genotoxicity 
and sustain a relation between this possible non-invasive marker of colorectal 
cancer risk with both dietary habits and colonic ecosystem.