A newly released study showed that prostate cancer survivors who took daily soy supplements did not have lower risks of the disease returning compared to men who took a placebo.
These findings contradict other laboratory, animal and observational (looking at patterns) studies on soy supplements.
"Tell your doctor about all the supplements you’re taking."
Maarten C. Bosland, DVSc, PhD, of the University of Illinois at Chicago, and colleagues conducted a randomized trial between July 1997 and May 2010.
The aim of this study was to learn if daily consumption of a soy supplement for two years would reduce the rate of prostate cancer recurrence (return) as measured by prostate-specific antigen (PSA) levels in prostate cancer survivors who had had their prostates removed.
PSA is a protein that's released from the prostate. High PSA levels can signal prostate cancer.
This study involved 177 men who took part in the study at seven centers around the US.
These participants were randomly assigned to have a daily beverage powder containing 20 grams of soy protein isolate or a placebo containing calcium caseinate.
The men started taking the daily supplement within four months after they'd each had surgery to remove the prostate, and they continued taking it for up to two years.
To measure progress, PSA tests were taken every two months during the first year and every three months in the second year.
The researchers were looking to see if participants developed what’s known as a biochemical recurrence, which is defined as a PSA of 0.07 ng/mL or more.
About the same number of men from each group saw their prostate cancer return, including 22 men who were taking the soy supplements and 23 men taking the placebo.
The period of time until the cancer returned was shorter in the group of men taking the soy supplement — 31.5 weeks compared to 44 weeks for those who didn’t take the supplement.
Nutrition and preventive medicine expert Deborah Gordon, MD, told dailyRx News that the study points out "...that associations seen in observational trials (that men eating soy suffer less prostate cancer) and animal trials do not necessarily correlate with the outcomes in clinical interventions."
She continued, "In general, I see no role for soy, particularly now that genetically modified soy is so prevalent, if not universal, in a health-conscious diet, and resort to other recommendations for reducing risk of primary and secondary prostate cancer," said Dr. Gordon, who is an integrative physician at Madrona Homeopathy in Ashland, Oregon.
She recommends to her patients a diet that relies on "...healthy sources of meat, fats, fruits and vegetables as a reasonable strategy for someone seeking a nutritional response to a risk of prostate cancer."
This study was published in the July 10 issue of JAMA.
This work was supported in part by National Institutes of Health. Minor support was provided by the Prevent Cancer Foundation and the United Soybean Board. Solae LLC provided the intervention materials.
One of the study's authors, Dr. Taneja, has served as a consultant for Eigen, Gtx and Bayer and, as a speaker for Janssen, receives royalties from Elsevier and is a clinical trial investigator for Steba. No other disclosures were reported.