Soy does not protect men from prostate cancer recurrence. Epidemiologists have long noted that prostate cancer is much lower in Asian countries. One hypothesis to explain this difference is dietary. People in China, Japan and Korea consume far more soy-based foods than men in the United States.
Because soy is high in phytoestrogens, some researchers thought that these isoflavone compounds might help block prostate cancer activity. A study conducted at seven centers in the U.S. recruited 177 men who had undergone radical prostatectomy after a cancer diagnosis. They were randomized to receive either a soy protein beverage or a placebo drink containing milk protein. PSA measurements were taken every few months to detect prostate cancer recurrence.
There was no difference between the two groups. Almost 30 percent of the subjects had a recurrence within two years. The researchers remarked that epidemiological evidence is based on people exposed to soy foods throughout their lives. Starting soy supplements after prostate cancer diagnosis does not appear to offer any benefit. Perhaps the prostate protection occurs only for a man who ate soy as a boy.
