Testicular StAR levels were not significantly different between the phytoestrogen-rich vs the phytoestrogen-free fed animals.
These results indicated that consumption of dietary phytoestrogens resulting in very high plasma isoflavone levels over a relatively short period can significantly alter body and prostate weight and plasma androgen hormone levels without affecting gonadotropin or testicular StAR levels. The findings of this study identify the biological actions of phytoestrogens on male reproductive endocrinology and provide insights into the
protective effects these estrogen mimics exert in male reproductive disorders such as benign prostatic hyperplasia and prostate cancer. (emphasis added)
Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5alpha-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague-Dawley rats -- Weber et al. 170 (3): 591 -- J
A recent study published in a 2007 issue of
Cancer Epidemiology Biomarkers and Prevention, however, had male bodybuilders ditching their soy protein-powder jugs. The researchers from the University of Medicine and Dentistry of New Jersey stated in their abstract that males taking 56 g of soy protein powder for four weeks experienced a 19% decrease in testosterone levels. Journalists duly reported that soy decreased testosterone levels by 19%, which triggered widespread concern among males. Yet, upon further analysis of the data, it’s clear that this statement about a 19% decrease is false.
The actual decrease was only 4%, and upon further analysis of the data, there are severe flaws in the study. For instance, one subject who was allowed to participate in the study had testosterone levels that were about 200% higher than the average testosterone levels of the other subjects. In fact, his testosterone levels were similar to those of someone using anabolic steroids, or just coming off of a cycle of steroids. The fact that his testosterone levels steadily dropped over the course of the study by 60% suggests that this subject had recently stopped taking anabolic steroids to participate in the study. If you remove his data from the study, it becomes obvious that there wasn’t even a 4% decrease in overall testosterone levels. In reality, the majority of the subjects experienced either a small increase in testosterone levels or no change in their testosterone levels at all during the four weeks of taking soy protein. Shocked at how sloppy these researchers were? Don’t be. What else would you expect from a group of researchers who misrepresented their data in the abstract?
Scientific Fact: Good research proves that soy protein will not affect your testosterone levels.
Myth: Soy can’t offer the muscle-building benefits that whey can.
Truth: Brand-new research finds that soy can boost nitric-oxide levels. Researchers from Virginia Polytechnic Institute and State University (Blacksburg) reported that the soy phytoestrogen, genistein, increased the amount of nitric oxide synthase (NOS) produced by the blood vessels. Since NOS is the enzyme that converts arginine to NO, this led to a significant increase in NO levels. Since soy also happens to be high in arginine, using soy protein is a smart way to boost NO levels and therefore blood flow to muscles, such as before workouts. An increase in blood flow during workouts delivers more nutrients, oxygen and hormones to the muscles.
In addition, research finds that soy better protects your muscles from the oxidative damage that typically follows exercise and can lead to better muscle recovery after exercise as compared to whey. The 2004 Ohio State University (Columbus) study comparing soy and whey protein from protein bars showed that the guys eating the soy protein bars experienced better antioxidant protection following exercise. Another 2004 study also found that when trained men supplemented with 40 g of soy protein before working out for four weeks, they experienced better antioxidant protection following weight workouts as compared to whey protein.
Muscle & Body Magazine