Part of the reason prostate cancer rates are so much lower in Asia than in Western countries is often credited to the soybean and numerous studies have found a relationship between the consumption of soy foods and a reduction in prostate cancer risk in men.
For years however, there has been controversy surrounding the use of soy and how it may cause, stimulate, or otherwise aggravate hormone-drive cancers, such as prostate, breast, and uterine cancers. The arguments center around the fact that soybeans contain soy isoflavones often referred to as phytoestrogens. These isoflavones have extremely mild estrogen-like effects, which is one reason some people are reluctant to eat soyfoods: they are concerned the isoflavones will stimulate estrogen activity and promote tumor growth in the prostate. See: Can soy cause cancer?
Many experts claim soy is a highly nutritious and beneficial food that does not contribute to prostate (or any other) cancer. One reason they make this argument is that soy contains an isoflavone called genistein, which was found to slow the growth of prostate tissues in BPH and to interfere with the growth of prostate cancer cells. (Raffoul 2006; Kazi 2003)
Soy and Prostate Studies
There are a number of studies on soy and its impact on prostate health and most are generally favorable.
- In animal studies, soy has hindered the ability of prostate cancer cells to spread by not allowing them to detach from the primary prostate tumor and metastasize to create new tumors. (Am Assoc Cancer Research 2008) Studies of large populations show that when people consume more foods rich in genistein, there is less prostate cancer, and vice versa; with lower intakes of genistein there are higher rates of cancer. (Moline 2009)
- The results of an analysis of 13 studies published in Nutrition and Cancer showed that both genistein and another isoflavone found in soybeans, daidzein, were associated with a lower risk of prostate cancer. The investigators noted that soy food consumption could reduce the risk of prostate cancer, and that in their analysis tofu illustrated a significant benefit over soybean milk, miso, and natto. (Hwang 2009)
- A Stanford University School of Medicine team of scientists explored the impact of genistein on prostate cancer cells and published their findings in the International Journal of Cancer. They found that genistein inhibited the synthesis and actions of prostaglandins, which are known to stimulate the growth of prostate cancer. The genistein therefore demonstrated an ability to reduce the risk of prostate cancer. (Swami 2009)
- In a study published in 2007 in Cancer and Epidemiological Biomarkers Preview, researchers evaluated the biological activity of an over-the-counter soy protein supplement in the blood of 12 healthy male volunteers ages 25 to 47 and in an estrogen receptor test. (Goodin 2007) The men consumed two scoops (56 grams) of pure soy protein powder daily for 28 days. Their testosterone levels decreased a mean of 19 percent during the trial and then increased within 2 weeks after they stopped taking the soy. The authors concluded that soy protein powder decreases testosterone levels in healthy men and acts as an estrogen-beta agonist. For those with concerns that high testosterone levels may prompt prostate cancer development, this study illustrates that soy protein may actually decrease levels of the hormone.
- In a 2009 study published by the American Society for Reproductive Medicine, the researchers found that soyfoods, isolated soy protein (like that found in powdered protein supplements), and soy isoflavone supplements have no significant impact on the levels of testosterone in men. (Hamilton-Reeves 2009) Once again, this study indicates that soy does not have a negative influence on testosterone levels and a possible association with prostate cancer development.
Despite the above studies, there is still a strong movement against soy in the US given its potential estrogenic effect. Part of the issue with soy may come down to the level of processing, the type of soy (unfermented or fermented soy) and how much you eat. Asian populations actually eat less soy than we think (see The China Study and Soy) and it is possible that the US population is just eating too much of the food and overdosing on the product. Hormones strive to be in balance and anything that upsets the balance is likely to have a potentially negative health effect. (See: How much soy is healthy?)
Soy Is Like Chocolate
How is soy like chocolate? Every once in a while a study comes out touting a health benefit of chocolate. Of course, in small print they tell you that the chocolate must be dark unsweetened chocolate and you should only eat an ounce or two, but hey, it’s chocolate! Chocolate is a good source of folic acid, copper, magnesium, and the antioxidant polyphenols. But chocolate also has its downsides: it’s high in saturated fat, it has lots of calories, and cocoa butter can raise serum cholesterol concentrations. Chocolate is rich in oxalates, which may contribute to the development of kidney stones, and its high content of methylxanthines may promote the development of benign breast disease and migraine.
The point is, a small amount of the healthiest type of chocolate several times a week is fine, even good for you. Eating milk chocolate bars all day, however, is not healthy. When it comes to soy, there are hundreds of articles written by both advocates and opponents of soy, with both sides presenting some pretty convincing arguments as to whether soy should be enjoyed regularly or in moderation for prostate health.
Other Benefits of Soy
Soy has a number of benefits outside of prostate health.
- Isoflavones in soy foods may inhibit the breakdown of bone. Soy contains the isoflavone daidzein, a compound that is very similar to the drug ipriflavone, a drug is used throughout Europe and Asia to treat osteoporosis.
- Intake of soy foods could reduce the risk of colorectal cancer. (Yang 2009)
- A recent study (January 2010) looked at the effect of soybean foods on diabetes. After reviewing both animal and clinical and epidemiologic studies, the investigators found evidence that fermented soy foods may be better for preventing or delaying the progression of type 2 diabetes compared with nonfermented soy foods. (Kwon 2010)