Soy shows some potential for men
with prostate cancer

Soy products and some of its components—which are called isoflavones—have been widely studied for their effects on cancer, including prostate cancer. Researchers believe that some isoflavones (in particular one called genistein) may have estrogen-like effects. What isn’t yet clear is whether isoflavones have the ability to stimulate or stop the effects of the hormone estrogen.

Here are results of some studies which point to the potential benefits in men with prostate cancer:

• Pendleton et al concluded from a Phase II study of 20 men with a rising PSA after prior local therapy that dietary intervention with isoflavone supplements may have biologic activity in men with biochemical recurrent prostate cancer. In this study, men drank soy milk containing 47 mg of isoflavonoid per 8 oz serving 3 times per day for a year. PSA had increased 56% per year before the men entered the study, and only increased 20% per year for the 12-month study period. While this was a small study, the decline in the slope of PSA results was statistically significant
• Yan and Spitznagel did an extensive review of all the available data (called a meta analysis) and concluded that dietary soy is associated with a reduced risk of prostate cancer. They also concluded that this benefit may be due to the type of products a man consumes and how much he consumes
• Ahmad et al studied the use of these isoflavones in conjunction with radiation therapy in men with prostate cancer. In this small study, men who had 200 mg of soy when they started radiation experienced less dripping/leakage of urine, less rectal cramping/diarrhea, and less pain with bowel movements after 6 months than men who did not take it. There was also a higher overall ability to have erections.

On the flip side, Hwang et al concluded in their comprehensive meta-analysis of five cohort studies and 8 case-control studies that consumption of soybean milk, miso, or natto did not significantly reduce the risk of prostate cancer.

Hopefully, researchers, nutritionists, and prostate cancer specialists will work together to provide guidelines for what types of foods and/or supplements are ideal for men with prostate cancer, and how much men should consume each day. Studies should also be conducted to determine if long-term consumption is safe for men with cancer.

When we last checked the National Institutes of Health clinical trial database, there were 11 new clinical trials that are being conducted in this area in men who have prostate cancer.

Updated 1/12

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Yan L, Spitznagel EL. Am J Clin Nutr. 2009;89(4):1155-63.