You may have heard here or there in the past few years about the potential protective benefits of soy. There have been many claims made about soy including that it might reduce the risk of developing prostate cancer.
So what do we really know about soy and prostate cancer?
Has It Ever Been Studied?
There have been just a few, small, less-than-perfect studies that sought to determine if soy gave any protection against the development of prostate cancer.
All of these studies have been retrospective studies. This means that researchers looked back in time at data instead of setting up an experiment to directly compare men who ingested soy versus those that didn't. Retrospective studies are always very difficult to accurately interpret and can end up being misleading.
What Have the Studies Shown?
Keeping the limitations of retrospective studies in mind, those studies that have been done have shown a small protective benefit associated with the intake of soy.
One study, called a meta-analysis, looked over the data of eight other studies that had already been completed and determined that, overall, these eight studies showed a modest amount of protection from prostate cancer development was gained with increased soy intake.
Additionally, it is hypothesized that Asian men may have overall lower rates of prostate cancer in part due to their much higher intake of soy than other men.
How Is Soy Thought to Work in the Body?
Soy contains compounds called phytoestrogens (such as flavones and isoflavones) that behave in a similar way to estrogen in the human body.
It is generally thought that these phytoestrogens work as a sort of balance against the effects of testosterone. Testosterone and other similar androgens (male hormones) are thought to promote the growth of prostate cancer cells. By reducing the influence of testosterone, phytoestrogens may slow the growth of prostate cancer cells.
The Bottom Line
So far, there has been no conclusive data showing that soy definitely affords protection against developing prostate cancer. However, several small, retrospective studies have shown that some protection might be gained.
It's up to you, with the help of your doctor, to determine if increasing your soy intake is the right thing to do or not.
Jacobsen BK; Knutsen SF; Fraser GE. Does high soy milk intake reduce prostate cancer incidence? The Adventist Health Study (United States). Cancer Causes Control 1998 Dec;9(6):553-7.
Kurahashi N; Iwasaki M; Inoue M, et al. Plasma isoflavones and subsequent risk of prostate cancer in a nested case-control study: the Japan Public Health Center. J Clin Oncol. 2008 Dec 20;26(36):5923-9. Epub 2008 Nov 17.
Yan L, Spitznagel FL. Meta-analysis of soy food and risk of prostate cancer in men. Int J Cancer. 2005 Nov 20;117(4):667-9.