In professional wrestling there’s a common expression, ‘the double turn’. This is when over the course of match the bad guy becomes good as the good guy turns bad.

We already know about testosterone’s slow move from the alleged cause of things like heart disease in men to the possible solution for it. But what about the other side of that coin? What about a hero to villain switch?

Well that seems to be what’s happening to soy. Once championed as a healthy alternative to dairy and a great source of protein for vegetarians and vegans, some are now questioning just how good it really is for us. Not least with the charge that soy reduces male hormone levels.

Some in the bodybuilding community already seem convinced. You might have heard the term ‘Soy boy’. It’s this generation’s version of Governor Schwarzenegger’s “Girly men” slap down. But is it fair? Can soy really turn you from a tower of power to a delicate flower?

Soy Ahoy!

Glycine max to give it its technical name, is a legume native to East Asia, which is poisonous raw but edible when cooked.

It’s popular in cuisine round the world because on the face of it soybean has a lot of nutritional upsides. It’s rich in B vitamins, iron and phytic acid for example, and in common with most meats is a complete protein Meaning it contains all nine amino acids we need to stay healthy.

So what’s the problem? Sounds beneficial enough. What exactly is the beef (substitute) here?

From a hormonal standpoint the issue is soy is estrogen-like. In other words it contains isoflavones, or derived phytoestrogens, which potentially mimic the female hormone’s effect on your body. The higher our estrogen levels the lower our T, so you can see why some guys are wary.

At his point you might be thinking, “Wait a minute, this article doesn’t really concern me. I’m not into soy sauce, tofu, edamame beans, anything like that.” Well you might want to think again.

Soy sneaks into most things we eat even if it doesn’t have a starring role. Anytime you see vegetable oil on an ingredients list for instance, chances are that’s soybean oil. There’s also soy based hydrolysed vegetable protein (HVP) which is used to enhance flavor in anything and everything.

Plus soy makes up a large percentage of the feed given to livestock. So it’s in the food chain even if we don’t take it directly.

Legume of doom?

Concern started thanks to studies like that from the University of Guelph in Ontario, Canada circa 2005. Here 35 men took a number of protein isolates, including those with both high and low soy content for 57 days. Hormone levels were recorded on days 1, 29 and 57.

Results showed a slight drop in serum T and dihydrotestosterone (DHT) in those taking either high or low soy doses, while estradiol rose.

Another study in 2008 from the Harvard School of Public Health explored soy intake’s possible influence on sperm concentration. 99 infertile men were tested to get a baseline reading, then over a period of 3 months, subjects ate high levels of 15 soy based foods.

[Editor’s Note: 99 guys? They could have found just one more and made the percentage calculations a bit easier.]

Researchers found what appeared to be a negative relationship between soy consumption and sperm health, with those eating the most performing worst.

In an interesting case study from 2011 a 19 year old diabetic man reported a sudden loss of libido and erectile dysfunction while on a soy heavy vegan diet. His T and DHT levels were also low. Within one year of lowering the amount of soy in his diet symptoms had gone.

It’s worth pointing out however that this subject had an underlying metabolic condition and at the time was using soy for nearly all his protein needs, eating 10 times an average volume.

Soy it ain’t so

Before you go on panicky hunger strike to avoid any trace of soy for the good of your T, know that most of these scary results involved people being given very high amounts of soy. Well above the 2 servings a day currently recommended.

A 2010 large scale review by a team at Loma Linda University of 9 human and animal studies for example found there was no evidence the isoflavones in soy had feminizing effects on the male body.

Similarly that same year a meta-analysis of research in this area, involving 15 control groups, 32 reports and 36 treatment groups was also reassuring. It reported neither soy foods nor isoflavone supplements alter T levels in men. 

93% of soy in the U.S is currently genetically modified. It’s easy enough to stay natural though. Just look for the word ‘organic’. GMO products can’t legally make that claim.

Soy Division

There’s been concern that if soy binds to the estrogen receptors in the body, it may increase the chance of estrogen fuelled conditions, such as breast cancer. Recent evidence however appears to contradict this however.

A massive study of 73,000 women in China, where soy is staple of the diet, found that subjects who took 13g of soy a day had a lower risk of developing breast cancer than those who ate just 5g.

One area where the latest data does suggest it might be worth keeping an eye on your soy intake is prostate health.

A study, published in November 2017, investigated the eating habits of 27,000 men, monitoring their health over 12 years. Worryingly, they report that those who ate high amount of the isoflavones found in soy were 91% more likely to get aggressive prostate cancer than men who ate lower levels.

Sounds damning, but there are a few caveats. Firstly those at risk were eating well above the average advised amount we mentioned earlier. Second, at this point there’s no direct cause and effect link, just an association. More work is needed to answer certain questions.

For example, why do Asian countries, where soy is a much larger part of the daily diet, traditionally have lower prostate cancer rates?


There’s really no conclusive evidence that soy is especially bad for your T. In fact larger, arguably more comprehensive studies say it’s not.

It’s certainly not the edible sex change some bros would have you believe.

Indications are problems only arise if you’re eating large amounts of soy over a long period of time. To an extent that’s true of everything though. You should always strive for a varied, healthy diet.

Maybe you’re still skeptical. That’s fine, by all means give soy the swerve. Plenty more complete proteins in the sea (and on land.) It’s tough to avoid altogether, but there’s no need to worry about the trace amounts you might be getting.

Write a comment