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Does Soy Make Men Sterile?

Soy isoflavones are believed to have estrogen-like effects in the body. As plant-based and vegetarian diets are slowly growing in popularity among men, should we expect male fertility to take a hit?

If you’re on a plant-based diet, soy is a huge source of protein. The bean is arguably one of the world’s most versatile — you find it in soy milk, imitation dairy products, tofu, soy sauce, and tempeh. What most people don’t know is that soy is also an additive in a myriad of other foods, including coffee whiteners, whipped toppings, fortified pasta and cereals, baked goods, and even processed and whole meat products.

In other words, you don’t have to be following a plant-based regime to consume soy.

Though some research suggests that chowing down on soybeans and soy products can boost heart health, prevent cancer, and help you maintain a healthy weight, other studies aren’t so sure of soy’s benefits.

A 2008 study published in Human Reproduction even linked soy-based foods to low sperm counts in men, sparking worries that all that soy was making men sterile. As soy becomes a staple in the American diet, it’s time to set the record straight.

Is Soy a Factor in Male Infertility?

Nearly a decade ago, some outlets reported that men trying to conceive might be best to simply avoid soy. However, WebMD cautioned taking the results of the study, which examined sperm samples from 99 men, as fact.

The truth is that although the findings sparked a lot of buzz the study had some serious shortcomings. For one, the men who ate soy products still had sperm concentrations within a healthy range. Their counts were marginally lower than men who ate no soy whatsoever.

Not to mention, soy-eating men were especially likely to have lower sperm concentrations if they were also overweight or obese. Since the study didn’t control for weight, it simply isn’t enough to rule out that being overweight or obese might be behind the low sperm concentrations.

Moreover, the small sample of men surveyed — only 20 participants said they ate soy foods twice a week or more — just isn’t enough to conclude that men who want to conceive should avoid soy products altogether.

Soy Isoflavones: Friend or Foe?

The culprit behind the brouhaha might very well be isoflavone, a plant compound found in soy that is believed to behave similarly to the female sex hormone estrogen in the body. Isoflavones bind to estrogen receptors in the heart, liver, brain, bones, and reproductive organs, causing a cascade of effects. The thinking was that men who consumed isoflavones would experience estrogen-like effects, including feminization, infertility, and erectile dysfunction — but that theory has since been disproven.

In the decade since the initial study was published, new findings have also emerged to suggest that soy may have drawn unwarranted attention. A 2010 study indicated that the quantity of isoflavone ingested has no noticeable effects on sperm quality in young men who are otherwise healthy.

If that’s not proof enough, consider this: men in Asian countries have been consuming high-soy diets for generations — and they’re still fathering children.

[Image via Shutterstock]

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