EFFECTS OF HIGH-RISK AND LOW-RISK DIETS ON GUT MICROFLORA-ASSOCIATED BIOMARKERS OF COLON-CANCER IN HUMAN FLORA-ASSOCIATED RATS

Formulated diets associated with a high risk (HR) or low risk (LR) for colon cancer were used to assess the effect of diet on putative metab olic biomarkers in human flora-associated rats: The HR diet was high i n fat and sucrose and low in calcium and fiber; the LR diet was low in fat and high in starch, calcium, and fiber. The nutrient-to-energy ra tio and energy intake were the same for both diets. Body and liver wei ghts were significantly higher in animals fed the HR diet possibly due to greater energy availability from far. Cecal weights were significa ntly higher in animals fed the LR diet, presumably due to a bulking ef fect of the fiber and increased bacterial biomass. The HR diet signifi cantly altered cecal bacterial enzyme activity: beta-glucuronidase act ivity increased 2.5-fold, and beta-glucosidase activity was halved. Am monia production and the bacterial metabolism of 2-amino-3-methyl-7H-i midazo[4,5-f]quinol (IQ) to 7-hydroxy-IQ (7OHIQ) were significantly hi gher in animals fed the HR diet. The HR diet, which contained factors common to diets consumed throughout the Western world, increased beta- glucuronidase activity, elevated cecal ammonia concentrations, and enh anced the genotoxic risk from 7OHIQ formation, three putative metaboli c biomarkers of colorectal cancer. The significance of the reduction i n beta-glucosidase is unclear.