Soy and Cancer: A Meta-Analysis

by Michael Greger, M.D.

Some studies suggest that soy consumption prevents cancer, some studies find no association and internet sites like Mercola.com suggest that ingesting soy actually causes cancer. (Joseph Mercola, who boasts the "#1 natural health website," just received a warning letter from the FDA ordering him to stop making illegal claims about the products he sells. See http://www.casewatch.org/fdawarning/prod/2005/mercola.shtml). So what does the balance of evidence show? That's where a meta-analysis comes in.

Instead of picking and choosing studies to suit one's agenda, meta-analyses look at essentially every study ever done on a topic and kind of pool the data all together. A meta-analysis of the effect of soy on cholesterol levels back in the '90s, for example, showed that the evidence of a cardio-protective role of soy was so strong that the FDA authorized a health claim on soy products that they may reduce the risk of heart disease. Now finally, published in a recent issue of the Journal of the American College of Nutrition, a meta-analysis on the role of soy in cancer prevention.

Researchers looked at three types of cancer: breast cancer, prostate cancer and gastrointestinal cancer (like colon cancer). Combining all the best published studies, they found highly significant reductions in cancer risk among consumers of soy products. Women of all ages who eat soy enjoy 22% less breast cancer (36% less for postmenopausal women!), male soy consumers are 34% less likely to get prostate cancer, and both men and women who consume soy reduce their risk of developing gastrointestinal cancer by 30%.[21]

The evidence is so strong that there is now another health claim before the FDA--soon we may see labels saying that soy protects against cancer as well.

REFERENCES

[21] Badger TM, et al. "Soy Protein Isolate and Protection Against Cancer." Journal of the American College of Nutrition 24(2005):146S-149S.