PRF1 and prostate cancer: The present study showed that substituting 3 oz of walnuts per day for fat sources in an Average American Diet significantly increased intake of γ-T and mono- and polyunsaturated fats and resulted in a significant decrease in serum α-T:γ-T, with a trend towards an increase in serum γ-T and PFP, in this population of older men at risk for prostate cancer.