Men who took soy supplements after having their prostate cancer removed were just as likely to see their cancer return as men who didn't take soy, in a new study.
"I think this study clearly demonstrates men in this particular situation… will not benefit," said Maarten Bosland, the study's lead author from the University of Illinois at Chicago.
According to the American Cancer Society, prostate cancer is the second most common cancer among men after skin cancer. It's estimated that one in every six men will be diagnosed with it.
Some doctors believed compounds found in soy - known as isoflavones - might help prevent prostate cancer, but more recent studies have found those and other nutritional supplements don't reduce the risk of developing the disease.
For the new study, published in the Journal of the American Medical Association, Bosland and his colleagues randomly assigned 177 men who'd had their cancerous prostates surgically removed less than four months earlier to drink either a soy or placebo beverage every day for up to two years between July 1997 and May 2010.
Although the vast majority of the participants reported following the instructions, the study was stopped during an early evaluation because there was no benefit seen with soy, Bosland said.
He and his colleagues found that 27 percent of the participants in the soy group ended up having their cancer return according to prostate-specific antigen (PSA) blood tests, which are used to check for evidence of cancer. That compared to about 30 percent in the placebo group.
"When we did the analysis and there was an absolute absence of the effect, I was a little surprised. But in a way, it was good because the outcome was clear," Bosland told Reuters Health.
"This adds to the evidence that nutrition supplements really aren't beneficial," said Dr. Eric Klein, chairman of the Cleveland Clinic Glickman Urological and Kidney Institute.
Other than undergoing regular PSA tests to check for a recurrence, Klein, who was not involved with the new study, told Reuters Health patients who had their prostate cancer removed have no promising options to help prevent the cancer from coming back.
But both Klein and Bosland said there is some evidence to suggest people who eat soy starting early in life may be less likely to develop prostate cancer in the first place.
"Those kind of studies suggested if you eat soy your entire life you may benefit from it," said Bosland.
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