Soy, a member of the pea family, is native to Southeast Asia, where it has been a staple food for 5,000 years and has been fermented into tamari soy sauce and miso for 2,500 years. MayoClinic.com describes soy as a mixed food and pharmaceutical. In addition to high-quality dietary protein, essential amino acids and fiber, soy provides lecithin and isoflavones, such as genistein, with estrogen-like properties that have important implications in male health and disease.
Meta-Analysis
Prostate cancer can become more aggressive in men in the presence of the male sex hormones testosterone and androgen, the counterpart to the female sex hormone, estrogen. Scientists at the U.S. Department of Agriculture's Grand Forks Human Nutrition Research Center in North Dakota reported in 2009 in the "American Journal of Clinical Nutrition" on the results of 24 research studies on the estrogen-like effects of soy isoflavones on men. The results documented that men who consume soy foods experience lower than average prostate cancer risk. The protection varied with the amount and type of soy foods consumed.
Androgen Receptors
The prostate gland contains receptors for androgen and estrogen, which males also produce, though in far smaller quantities than females. In 2007, Dr. J. Hamilton-Reeves at the Department of Food Science and Nutrition of the University of Minnesota in Minneapolis administered purified soy protein isolate to men who volunteered to undergo prostate biopsies before and after six months of daily doses. The results, published in the "Journal of Nutrition," showed that soy protein isolate selectively suppresses the prostate gland's androgen receptors. The researchers suggested that this effect of soy protein isolate might explain prostate cancer protection.
Estrogen Enhancement
In a separate study, the University of Minnesota researchers documented that soy products alter the metabolism of male estrogen in ways similar to the effects of soy on estrogen metabolism in postmenopausal women, in which soy enhances the activity of estrogen. The report, published in 2007, in the "Journal of Nutrition," proposes that soy consumption by men at high risk for prostate cancer might be useful in helping estrogen slow the progression of new cancers.
Heart Protection
According to a June 2010 MayoClinic.com report, the androgen and estrogen balance in men also might contribute to cardiac disease risk factors. Soy protein's estrogen-like properties have been investigated for their benefit against some cardiac risk factors, including weight loss, exercise performance enhancement, preventing inactivity caused by arthritis pain and age-related declines in brain function. Evidence suggests that dietary soy might decrease some of these cardiac risk factors.
Safety
MayoClinic.com warns that it is not known whether soy isoflavones have the same side effects as estrogen, such as an increased risk for blood clots. Until more research is done, it cautions you to consult your doctor before trying soy for any medical condition. Soy is considered a food, an herb or a supplement, depending on its form. It is not strictly regulated by the U.S. Food and Drug Administration. Strength, purity, safety, effects and side effects of products can vary.
References
- The Journal of Nutrition: Soy Protein Isolate Suppresses Androgen Receptors in Men at High Risk of Prostate Cancer
- The Journal of Nutrition: Soy Protein Isolate Increases Urinary Estrogens in Men
- The American Journal of Clinical Nutrition: Soy Consumption and Prostate Cancer Risk in Men
- MayoClinic.com: Soy (Glycine Max)
- MayoClinic.com: Soy Safety
