A DIET RICH IN FAT AND POOR IN DIETARY FIBER INCREASES THE IN-VITRO FORMATION OF REACTIVE OXYGEN SPECIES IN HUMAN FECES

Production of reactive oxygen species in the lumen of the colon, a pro cess that is influenced by nutritional factors, may be important in th e etiology of colorectal cancer. Because research on humans in support of this hypothesis is lacking, the objective of this study was to mea sure the effect of different dietary compositions on the in vitro oxyg en radical production in human feces. Over a period of 12 d, seven hea lthy subjects received a diet rich in fat (50%) and meat and poor in d ietary fiber. After a period of 1 wk, they received a vegetarian diet poor in fat (20%) and rich in dietary fiber. At the end of each study period, feces were collected and analyzed for in vitro oxygen radical production with dimethylsulfoxide as the free radical scavenger. The m ean hydroxyl radical production was 13 times greater in feces of subje cts when they consumed the diet rich in fat and poor in dietary fiber [52.7 +/- 29.5 mu mol/(g feces.h)] than when they consumed the diet po or in fat and rich in dietary fiber [3.9 +/- 3.9 mu mol/(g feces.h); P < 0.05]. This difference was associated with a 42% higher fecal iron concentration when they consumed the first diet (7.0 +/- 19.2 mu mol/g feces) than when they consumed the second (4.9 +/- 1.9 mu mol/g feces ; P < 0.05). The results of this study confirm that diets high in fat and meat and low in fiber markedly increase the potential for hydroxyl radical formation in the feces, which in turn may contribute to an en hanced risk of colorectal cancer.