I promise this will be the last blog post on soy foods for a long time. Even though I am a strong advocate of a plant-based diet (vegetarian or vegan), I don't believe soy foods are any more essential to such a diet than garbanzo beans. I'm not saying soy foods aren't great - garbanzo beans are great too - they're just not the focus of this blog. A healthy plant-based diet is possible with or without soy foods.
However, there is some confusion regarding soy foods and fertility. Because soy is loaded with isoflavones (plant-estrogens that can mimic estrogen), it is believed to affect the likelihood of pregnancy. Some studies have shown soy estrogens have no impact whatsoever on a woman trying to conceive, as soy foods do not interfere with menstrual cycles or ovarian function.
This makes sense because soy estrogens (along with other plant-estrogens) only raise estrogen levels when they are low. This also makes sense when we look at Asian women, who consume more soy foods than any other people group and yet have an extremely low prevalence of infertility. So low in fact, certain Asian countries have to put limits on population growth. (Obviously, soy is not hindering fertility in China).
There is a recent study (July 2008) that has linked soy foods with a decreased sperm count in men (published in the Journal of Human Reproduction). However, they found that men who were overweight or obese experienced a significantly lower sperm count than men who had healthy weights. One of the reasons for this is because fat cells, even in men, produce estrogen, which can hinder sperm production in men. Considering that 72% percent of the men with decreased sperm counts were overweight or obese, I would say this seems to be more of an impediment to fertility than soy consumption.
On a personal note, my husband and I both consumed tofu pretty regularly before we had our daughter, and we had no problem getting pregnant. (That was also when my husband was in the best shape of his life!)
So I would conclude that a healthy weight in men is more important than soy intake. And a plant-based diet - with or without soy - is the best fertility diet.