Shift from a dairy product-rich to a dairy product-free diet: influence on cytotoxicity and genotoxicity of fecal water--potential risk factors for colon cancer.

Several epidemiologic studies have suggested that dairy product intake is associated with a decreased incidence of colon cancer. To determine whether the cytotoxicity and genotoxicity of the aqueous portion of human stool (two potential risk markers for the disease) were affected by a change in dairy product intake, 18 healthy male and female volunteers were randomly divided into two groups. In a crossover design, the volunteers shifted from their normal dairy product-rich diet to a dairy product-free diet. Nutritional analysis of the food consumed during the study period showed a significant decrease in energy intake from 9000 to 7866 kJ/d because of a decreased intake of protein and fat. Carbohydrate and fiber intakes remained unchanged during the intervention. Calcium intake decreased significantly from 1488 to 372 mg/d, with similar significant decreases in phosphate and vitamin D intakes. Cytotoxicity of fecal water, analyzed by the HT-29 cytotoxicity assay, indicated a significant decrease in cell survival from 34% to 20% when dairy products were excluded from the participants' diets. Single-cell gel electrophoresis (COMET assay), used to analyze genotoxicity of fecal waters, indicated no differences brought about by the dietary intervention. In conclusion, our findings indicate that a shift from a dairy product-rich to a dairy product-free diet resulted in a significant effect on an accepted risk marker for colon cancer and may suggest that the mechanism by which dairy products are protective is at the level of tumor promotion rather than initiation.