Does Eating Soy Foods Cause Male Infertility?

Does eating soy foods lead to male infertility? A new study raises this important question. Soy has become a meat substitute and a popular source of protein for people eating a vegetarian or vegan diet, but some experts are concerned about the possible health effects of eating too many soy foods. Should men cut back on how much soy they eat?

Does Eating Soy Cause Male Infertility?

In a study published in the journal Molecular and Cellular Endocrinology, researchers fed a group of male mice a diet rich in soy foods from the time they were born until they became adults. Another group of mice ate a diet that was soy free. At the end of the study, they found that the mice that had munched on a soy diet had sperm counts that were a twenty-five percent lower than their non-soy eating counterparts. Their litter sizes were also 21 percent smaller.

Although this research was carried out in mice, a study carried out using human subjects found that men who ate a soy rich diet had lower sperm counts. Studies show that soy also lowers testosterone levels in men who eat it in abundance.

How Does Soy Cause Male Infertility?

Soy is rich in two isoflavones called genistein and daidzein. These isoflavones have phytoestrogen type effects in the human body - meaning they mimic the actions of the female hormone estrogen. This is of concern since high levels of estrogen could throw off levels of the male hormone testosterone. Testosterone is involved in sperm production and low levels of testosterone decrease male libido which could contribute to male infertility.

What's Good about Eating Soy?

There's some evidence that a soy rich diet reduces the risk of heart disease, boosts bone density, and even helps to reduce blood pressure. It's also a good source of low fat protein. The testosterone lowering effects of soy could have positives for men since decreasing testosterone levels reduces the risk of prostate cancer according to some studies.

Should Men Stop Eating Soy?

If soy causes male infertility, should men stop eating it? Some experts argue that this most recent study where mice were given soy continuously from conception to adulthood doesn't mimic the way humans eat soy - and that there's little danger of male infertility when soy is eaten in moderation. It's not completely clear whether soy is a cause of male infertility, but men who are having problems conceiving should limit how much soy they eat until more is known.

References:

http://www.foodnavigator.com/Science-Nutrition/Soy-again-linked-to-male-infertility-Mouse-study
Hum Reprod. 23 (11): 2584'"90.