Soy Consumption May Help Men Reduce PSA Levels.

A diet rich in soy may reduce levels of serum prostate-specific antigen (PSA) without reducing testosterone levels, according to a new study conducted by researchers from the Cancer Research Center of Hawaii and published on line by European Journal of Clinical Nutrition, June 14, 2006. Low prostate cancer incidence and high soy intake in Asian countries suggests a possible protective effect of soy foods against prostate cancer.

Twenty-four men with an average age 58 (+ or - 7.2 years) were randomized into two study groups. One group received a high-soy diet (two servings per day) and the other a low-soy (normal) diet for three months. After a one-month washout period, the groups crossed over to the other treatment for an additional three months. Blood was drawn from each subject four times and urine collected five times during the study. Samples were analyzed for serum testosterone and PSA by radioimmunoassay. Compliance was assessed by calendars, dietary recalls and urinary isoflavone excretion.

During the high-soy diet, dietary isoflavone intake and urinary isoflavone excretion increased significantly compared to the low-soy diet. A 14% decline in serum PSA was seen during the high-soy period, with no changes in testosterone. In addition, compliance with the intervention was high, based on dietary calendars and blood tests, demonstrating the feasibility of the intervention.