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Could soy products stop prostate cancer from returning?

Kathleen Blanchard's picture
Soy products tested for effect on prostate cancer recurrence in randomized study

Men treated for prostate cancer are often advised to make dietary and lifestyle changes that can minimize the chances that the disease will return. Research findings published in the Journal of the American Medical Association (JAMA) explored the association between soy consumption and prostate cancer among men who had undergone radical prostatectomy.

Prostate cancer is the second leading cause of cancer deaths among men in the United States making it important to find lifestyle interventions that can help prevent the disease.

Some studies have suggested soy protein might be beneficial for thwarting prostate cancer but until now the theory had not been tested in randomized control human trials.

Observational reports have found higher rates of prostate cancer in the Western and other countries, with lower rates in Asia where soy products are more widely consumed.

According to the study authors, 48 to 55 percent of men diagnosed with prostate cancer take some form of dietary supplement including soy, presumably to obtain the anti-cancer benefits that comes from isoflavones, though whether they help ward off cancer is unknown.

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Maarten C. Bosland, D.V.Sc., Ph.D., of the University of Illinois, Chicago and colleagues performed a randomized controlled study to find out if constituents of soy protein can stop prostate cancer from returning among men at high risk; following prostate cancer surgery.

For the study, 177 men from 7 centers throughout the U.S were given either 20 grams of soy protein in the form of a beverage or placebo beginning 4 months after surgery. The supplement was continued for 2 years. The study took place from July 1997 to May 2010.

PSA testing was initially done at 2-month intervals. After the first year, the men’s levels were checked every 3-months.

What is interesting about the study, in addition to the fact that soy was no benefit for preventing prostate cancer recurrence, is that it is contradictory to observational epidemiological and animal studies.

The researchers say a possible explanation is that “…in both epidemiological studies and animal experiments, soy exposure typically occurred for most or all of the life span of the study participants or animals”, making it possible that soy does help prevent prostate cancer when consumed early in life. There are no reports on the benefits of soy for prostate cancer prevention when it is started later in life.

JAMA. 2013;310(2):170-178. doi:10.1001/jama.2013.7842.

Image credit: Wikimedia Commons