Soy Protein Lowers Testosterone in Strength-Training Men – See more at: http://w
The soy industry is putting a positive spin on a recent study out of the University of Connecticut1, but why they haven’t tried to spin it deep into the ground is a mystery to me.
In a randomized cross-over, placebodesigned study, researchers compared the estrogen production of men drinking soy protein to those drinking whey. They looked at changes in estradiol concentrations after only fourteen days, and reported some good news―the soy drinkers did not end up with more of the female hormone. The researchers did, however, find lower testosterone levels and higher cortisol levels in the soy drinkers. In other words, less of the manly hormone and more of the stress hormone. Sounds like stressed out soy boys to me!
For years top body builders such as the late Vince Gironda touted diets rich in eggs, raw milk, red meat and other animal products while warning about the dangers of soy protein.2 In today’s soy-pushing climate, the U Conn researchers describe these legitimate concerns of Gironda and others about feminization and testosterone depletion as “fears” that “largely stem from body building mythologies.”3
BAD FOR BODY BUILDERS
Other studies have shown that soy protein is less effective for body builders than whey protein because its amino acids are more likely to go into splanchnic circulation (stomach, small intestines, colon, liver, pancreas and spleen) than into peripheral regions such as muscle tissues.4,5 This makes sense because whey protein provides greater amounts of the branched chain amino acids (BCAAs) leucine, isoleucine and valine as well as more methionine and lysine, all of which are critically needed for muscle building.6-9 Researchers have also found the low BCAA content of soy protein adversely affects muscle building by disrupting both leucine signaling10 and the activation of myogenic translation initiation factors. 11-14
Prior to the U Conn study, only one previous study compared the effect of soy and whey protein supplementation on the hormones of men doing resistance training.15 That study reported “no significant differences” between the soy and whey groups for total testosterone, free testosterone and sex-hormone-binding globulin (SHBG) after twelve weeks of supplementation. But as the U Conn team suggests, soy may well put testosterone at risk. In fact, over the past few decades, many researchers have found that phytoestrogens have adverse effects on both the production and utilization of hormones in males.16-18 Indeed, scientists have even induced “testosterone deprivation” in animals simply by feeding them diets rich in soy isoflavones.19
For the most part, the soy industry has tried to promote any testosterone-tanking effects as beneficial. Just as they promote hormonal changes that can lead to anovulatory cycles and infertility in women as valuable tools in the war against breast cancer, they tout testosteronelowering in men as protective against prostate cancer and atherosclerosis.20,21
Although the possibility that soy foods or supplements could prevent these deadly conditions tends to make headlines, few men hear that the downside is demasculinization. Testosterone might appear to be just a macho thing, but it’s a vital hormone for growth, repair, red blood cell formation, healthy sleep cycles and immune function, in addition to sex function.22 And low levels of testosterone have also been linked to low thyroid function, another unwanted and common side effect of soy consumption. Low thyroid function leads to loss of libido in both men and women.23
Perhaps the most startling study came out of the University of North Carolina at Chapel Hill a few years back. Completed for the National Cancer Institute, it found soy-eating men experienced “nipple discharge, breast enlargement, slight decreases in testosterone and hot flashes.” In an attempt to downplay these rather sensational findings, lead researcher Steven H. Zeisel, MD, reported to The Washington Post that nothing “serious” was found, because they administered doses up to thirty times what might get from “normal foods.” To reassure men, he stated, “I don’t think there are a lot of estrogenic worries. Your testicles will not shrink and you won’t have massive breast enlargement.”24
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