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July 2013

Soy May Not Reduce the Risk of Prostate Cancer Recurrence

Contrary to previous findings, a new study suggests that soy consumption may not reduce the risk of prostate cancer recurrence.

Soy contains protein, isoflavones and fiber, all thought to provide health benefits. Soy is an excellent source of dietary protein, including all essential amino acids. Soy is also a source of lecithin or phospholipid. Soy isoflavones and lecithin have been studied scientifically for numerous health conditions. Several large population studies have asked people about their eating habits and reported that higher soy intake (such as dietary tofu) is associated with a decreased risk of developing various types of cancers, including breast, prostate and colon cancer. However, other research suggests that soy does not have this effect. Until better research is available, it remains unclear if dietary soy or soy isoflavone supplements increase or decrease the risk of these cancers.

In a recent study, researchers randomly assigned 177 men at high risk of prostate cancer recurrence to receive a beverage powder containing 20 grams of soy protein isolate or placebo daily. Each participant started treatment within four months of initial prostatectomy and continued for a maximum of two years. Prostate-specific antigen (PSA) measurements were taken every two months within the first year of treatment, and then every three months for the second year.

The study was halted before completion due to lacking treatment effects. Within two years of entering the study, 28.3 percent of participants developed prostate cancer recurrence, with 27.2 and 29.5 percent developing in the soy and placebo groups, respectively. The authors noted that adverse effects were lacking.

The authors concluded that soy supplementation may not reduce the risk for prostate cancer recurrence. Additional studies are necessary to further evaluate these findings.

In additional to soy, many other integrative therapies have been studied for their potential to reduce the risk for prostate cancer. Initial evidence suggested that selenium supplementation may reduce the risk of developing prostate cancer in men with normal baseline PSA levels and low selenium blood levels. However, additional study showed an apparent lack of benefit. Further research is required before firm conclusions can be made.

For more information about integrative therapies with evidence of benefit for prostate cancer risk, please visit Natural Standard's Comparative Effectiveness Database.

For more information about soy, please visit Natural Standard's Foods, Herbs & Supplements Database.

To comment on this story, please visit Natural Standard's blog.

References

  1. Bosland MC, Kato I, Zeleniuch-Jacquotte A, et al. Effect of soy protein isolate supplementation on biochemical recurrence of prostate cancer after radical prostatectomy: a randomized trial. JAMA. 2013 Jul 10;310(2):170-8. doi: 10.1001/jama.2013.7842. 
  2. Natural Standard: The Authority on Integrative Medicine. 

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