Diets rich in soy products may reduce the risk of prostate cancer (PCa). Daidzein, the major isoflavone present in soy germ, can be metabolized by the gut microbiota into equol. The effects of daidzein and equol on PCa have not been well studied. The objective of this study was to investigate the effect of feeding 2% soy germ, 92 ppm daidzein, or 88 ppm equol diets on the progression of PCa in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model. 3-week old male C57BL/6 X FVB TRAMP

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... mice were weaned from our breeding colony and immediately acclimated to an AIN-93G control diet for one week. At 4 weeks of age, mice (n = 30 per diet group) were randomized to one of four pelleted study diets until 18 weeks of age. Unexpectedly, we did not detect any statistical differences in cancer incidence between diets. We suggest that these results are due to the physical attributes of the pelleted diets in the current study. Mice fed pelleted diets had reduced food intake and significantly decreased body weights (p < 0.001) compared to previous studies. A reduction in food intake is known to reduce cancer incidence in a number of cancer models and is likely to have contributed to the decrease in expected cancer incidence in the current study. In conclusion, we suggest that the hardness of the diets pellets could result in a decreased cancer incidence in TRAMP mice.