Soy has gradually become the darling of the nutrition world. In fact, soy-based foods have played an integral role in East Asian diets for centuries. Soy itself, and its many derived foodstuffs are highly esteemed for being an inexpensive alternative source of protein. In recent decades Soy has enjoyed an uptick in popularity among health-conscious individuals in Western cultures. This is important because Soy is the only widely consumed food containing biologically relevant levels of isoflavones; this means that Soy has the potential to induce Estrogen-like effects on those who consume it. What does this say for men? What effects, if any, will Soy consumption have on men’s Testosterone levels? Let us dig deeper.
SOY IS EVERYWHERE!
People are often unaware of how much Soy they are in fact consuming. The average American consumes over 120 pounds of Soy per year! Once you begin reading food labels with Soy in mind, you will find that soy and soy derivatives are everywhere. Even more surprising is the fact that most of the soy we consume is not labeled as such. You will find inordinate amounts of soy embedded in animal products that most consumers eat daily. The most bewildering fact is that none of this soy content is listed because it gets there through the feed that animals receive.
Because of this, you will find high amounts of soy in chicken, eggs, pork, beef, and even cheese. Processed food products also contain elevated levels of soy and soy derivatives. For example, the oil used in the manufacture of salad dressings is more often than no soybean oil. Various filler products, such as soy lecithin, enjoy widespread use in the pre-packaged food industry.
Soy is everywhere; from baby food to hamburger patties. Soy protein is cheap, and it often lauded for its many beneficial effects. Yet some men around the world are beginning to worry about the elevated levels of dietary soy due to widespread rumors that soy is capable of inducing estrogenic effects on the male reproductive hormone system, specifically on testosterone.
SEX HORMONES AND SOY
Testosterone and Estrogen are the primary sex hormones in humans, and they are vital to much more than just physical appearance. General wellbeing, as well as sex drive, energy metabolism, muscle mass generation, bone density, and aging, are related to some degree to our sex hormone production. It is often erroneously thought that sex hormones are gender specific; that is, that only males have testosterone and only females have estrogen. The truth is that a delicate balance of both testosterone and estrogen is needed in both sexes. In fact, all estrogen is synthesized from testosterone in the liver, brain, and muscle cells of the body.
However, testosterone does predominate in men where it is known to increase lean muscle mass, bone density, and enhance cardiovascular and neurological function. As men age, a shift in sex hormone balance occurs. Men begin producing less testosterone and estrogen becomes more predominant. This shift causes men to experience diminishing musculature, increased bone fragility and markedly reduced libido. Additionally, various studies have linked this shift in sex hormone prevalence to the development of several chronic disorders such as cardiovascular disease, depression, diabetes, and prostate cancer.
So, what are the health implications if soy products, as is believed by many, can accelerate the pace at which this shift naturally occurs? Does soy actually affect the presence or absence of testosterone and estrogen in men?
SOY ISOFLAVONES AND PHYTOESTROGENS
Each gram of soy protein of the type generally found in food products contains, on average, around 3.5 milligrams of isoflavones. A typical male can ingest on a daily basis as much as 50 milligrams of isoflavones through soy consumption.
This is alarming to some because Isoflavones are di-phenolic chemical compounds that are found to readily bind to estrogenic receptors in the brain and exert strong estrogen-like effects. For this reason alone, isoflavones are considered strong phytoestrogens, or estrogens not generated by the endocrine system. The two primary isoflavones found in soy protein are Genistein and Daidzein.
Initial studies into the effects of these substances found that in women at least, they function as selective estrogen receptor modulators because they have no impact on many biological processes that are affected by estrogen. Isoflavone classification as selective estrogen receptor modulators is, however, an incomplete characterization because they exert non-hormonal effects that are relevant to various other pathologies. Find out more about Isoflavones and the potential for reduced sperm production in men here.
WHAT ABOUT ISOFLAVONE EFFECTS IN MEN?
Research into the potential effects of Isoflavone consumption in men is much more limited. However, some studies have been performed in an attempt to gauge isoflavone action on the inherent risk of developing prostate cancer. Because one of the primary factors associated with decreased risk of prostate cancer is a lower testosterone concentration, it has been strongly suggested that soy foods are capable of actively lowering bioactive testosterone levels in men. Is this true? We investigated soyboy extremely low levels of Testosterone in another article.
In an attempt to determine whether isoflavones exert estrogen-like effects in men by lowering testosterone levels, a recent Meta-analysis of 15 placebo-controlled treatment groups with baseline and ending testosterone measures concluded that no significant pooled effects of soy protein or isoflavone intake on testosterone levels in men were detected.
To be fair, some studies, such as one conducted in 2007 by Goodin, et al. reported significantly lowered serum testosterone levels in men after only four weeks of ingesting 56 grams per day of isolated soy protein. However, the study included no control group, did not specify the methods of assessing hormonal levels, and only 12 subjects participated. Another study published a 5% decrease in participant’s serum testosterone after six weeks in response to 120 milligrams a day of isoflavones from soy flour. This study, however, failed to provide essential and relevant information such as the baseline and ending hormonal measures of the control group and without these data is impossible to gather an informed conclusion. Further investigation will be needed to corroborate their results.
It is important to note that soy protein has been attributed with providing a plethora of health benefits such as lowering blood pressure and serum cholesterol levels. Soy protein can also boost your dietary fiber intake as well as help to cut down on saturated fat consumption. Soy foods are also an excellent source of various vitamins, minerals, and Omega-3 fatty acids. A study in 2002 reached a similar conclusion. Because of this and the fact that no statistically significant decrease in serum testosterone levels has been positively identified as a side effect of soy consumption, there is no reason to avoid its inclusion in a balanced diet.
- Nieschlag, Eberhard, and Hermann M. Behre. “Pharmacology and clinical uses of testosterone.” Testosterone. Springer, Berlin, Heidelberg, 1998. 293-328.
- Wikipedia article Soybean
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- Kuiper, George GJM, et al. “Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor β.” Endocrinology 139.10 (1998): 4252-4263.
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- FDA Revoking claim that Soy reduces heart disease
- BBC Claim Sperm counts could make Humans extinct mention Soy Products could be a factor