Does Soy and Soy Products Negatively Affect Fertility and Preconception Time?

Tania Tod's picture

This question might be interesting for vegans consuming soy products, and generally people who eat soy and are trying to conceive a baby.

Connection between soy and infertility or decreased fertility is somehow cemented in my mind, I am not sure why, but there must be a reason, right?

So, I decided to make a little “research”, and in this article I have listed the main premises I have learned. I hope you will enjoy reading it, and perhaps learn something new.

First of all – connection between soy consumption and infertility is half a myth – countries such as Japan or China, where soy products are consumed in large amounts do not have lower birth rates than countries, such as USA and European countries where soy products are usually not a part of a daily menu. Statistically, despite the fact that Asians consume more soy products, they do not have bigger problems when trying to conceive comparing to western world.

In addition, there are studies available that suggest that soy does not have negative effect on fertility.

In a study that was exercised 10 years ago, American researchers injected genistein in prepubescent rats. Their thesis was to effect fertility or menstrual cycle, but the result was that there were no significant changes shown in menstrual cycle, body weight, fertility alterations or number of male or female offspring.

On the other hand, another study suggests that genistein injections had an effect on males! Scientists compared effects of isoflavone genistein between human and mouse sperm, and they found out that that human sperm was more than 3 times likely to lose acrosomes an hour after genistein exposure than before exposure. (Acrosomes are the caps that enable sperm to penetrate the egg.)
Other studies suggest that soy actually lowers sperm count and several studies concluded that a diet rich in soy products may lower the sperm count by as much as half.

For example, scientist took a study group of 99 men who were suffering from fertility problems at that moment. Men who were on a daily basis consuming the most soy-based foods had the most significant impact on their sperm count. The leading conclusion behind this study is due to the chemicals known as isoflavones that are found in soy products and mimic the estrogen hormone.

As said before, people living in Asia consume much more soy product than Americans or Europeans. For this reason American researchers compared the level of soy that is consumed by Asian women, and they gave a soy supplement containing twice the level of plant estrogen consumed by Asian women, to monkeys. Scientists chose monkeys because monkeys have menstrual cycles similar to those of human females. The results suggested the following: no changes in menstrual cycle, including length, bleeding or hormone levels, and no changes in ovarian function.

However, there are also few studies available that suggest the opposite. A small number of studies in Report in The Journal of Clinical Nutrition have shown that high levels of soy can increase menstrual cycle length by an average of 2.5 days, decrease follicle-stimulating hormone and decrease leutinizing hormone. But, it is important to bring out that the participants in the study were drinking three 12-ounce glasses of soy milk (60 g soy protein equivalent to 45 mg of isoflavones) for a month. These are very high levels and therefore generate such results. The results cannot be applied to a ‘typical’ soy consumer who does not consume this much soy food.

In conclusion, I agree with researchers who believe the main problem lies in ‘overeating’. As with any other food and every other ‘thing’ in life: moderation is the key. Eating soy in moderation allows you to avoid any potential harm, as well as leaving room for variety in your diet. The more variety in your diet, the more likely you are to get all the important nutrients that your body needs in preconception time.