Soy Improves Prostate Cancer Outlook

Adding 2 Ounces Daily Improves PSA Levels in Afflicted Men

From the WebMD Archives

Sept. 24, 2004 -- A soy-rich diet, thought to prevent the development of certain cancers, may improve the prognosis for men diagnosed with prostate cancer. And the effect seems to be immediate.

Studies have found that adding about 2 ounces of soy grits a day to the diets of men diagnosed with prostate cancer caused a quick and noticeable improvement in their PSA levels. PSA, or prostate-specific antigen, is commonly used to screen for prostate cancer and for tracking the disease once it's been found.

In the latest study, Australian researchers find that adding about 2 ounces of soy each day for one month results in a 13% drop in total PSA and a 27% increase in the free-to-total PSA ratio in men with prostate cancer.

PSA exist in two forms, one bound to proteins and one that is free. Many studies have suggested that men with prostate cancer have lower free PSA levels and lower free-to-total PSA ratios, making the ratio a more specific measure of prostate cancer.

The study is published in this month's Urology.

The 29 men, who were scheduled for radical prostatectomy, ate the soy in four slices of bread containing soy grits -- soybeans that have been toasted and cracked into coarse pieces and eaten as a cereal or added to recipes.

They were compared to other men who ate either wheat grains not enriched with soy or a combination of soy and linseed. Their total PSA scores worsened by 40% and 21%, respectively. Their free-to-total PSA level worsened by 16% and 10%, respectively.

Soy Shakes Help, Too

This research, by scientists at Monash University, follows another study published in the May issue of the journal Prostate showing a reduction in PSA levels among men with early-stage prostate cancer -- the "watch and wait" category for this often slow-growing cancer -- who drank a little over 2 ounces of soy daily in a milkshake. In that three-month study, 20% of those men had a PSA drop of 3 or more points.

The suspected benefit from soy comes from its high amounts of isoflavones, phytochemicals believed to help prevent the development of certain types of cancer, including breast cancer.

"The way I explain it is that the isoflavones in soy keep cells from going rowdy," says researcher Nagi B. Kumar, PhD, RD, of the Moffitt Cancer Center in Tampa, who headed that study in Prostate. "Most cells function, mature, and eventually die off. But some cells are mutated, and they proliferate in a way that's pointless, progressive, and wild. That's what causes cancer, and soy seems to help stop this."

Quick Results

Kumar says she's not surprised by her findings or by the Australian findings showing PSA improvement, since many previous studies have indicated that a soy-rich diet can prevent cancer development.

"But I am surprised at the results observed after only one month," she tells WebMD of the Australian study. "That's pretty remarkable when you consider this disease has a long latency period -- there's something like 16 to 20 years before you see evidence of prostate cancer. If men regularly consume this amount of soy over a lifetime, it has the promise of significantly reducing their risk of prostate cancer."

Her advice: Eat like Japanese men, who have one of the world's most soy-rich diets and lowest rates of prostate cancer.

"That means eating about 2-3 ounces of soy, three or four days a week -- by way of food, not supplements," she says. "Soy grits are a very good form, but we especially recommend fermented products like soy milk, because they are better absorbed in the gut."

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SOURCES: Dalias, F. Urology, September 2004; vol 64; pp 510-515. Kumar, N. Prostate, May 2004; vol 59; pp 141-147. Nagi B. Kumar, PhD, RD, director of nutrition and cancer control researcher, Moffitt Cancer Center; associate professor, University of South Florida College of Medicine, Tampa.
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