Soy is an excellent source of plant-derived female hormones called phytoestrogens.
The type of phytoestrogen in soy is known as isoflavones. They have a very weak
effect on the body, compared to the natural hormone and have been used in helping
people with menopausal symptoms.
There are not many studies done on the effects of soy on fertility. Reports in
countries where soy products are consumed in large amounts indicate that the birth
rate is similar to if not more than in countries where soy is not routinely consumed.
A few studies suggest that high levels of isoflavones may decrease fertility by
interfering the levels of pituitary hormones which stimulate growth of the egg and
ovulation.
However, these are taken in very large amount which most people normally do not
consume.
Experimental studies on various animal species have indicated that eating large
amount of soy can have adverse effects on fertility. But there is no evidence to
suggest that these results are applicable to human.
Toxicity studies did not find variations in fertility from soy consumption in
healthy couples indicating that normal intake of soy is basically harmless.
As with any food, it is wise not to overconsume. If you have difficulty conceiving,
it is a good idea to limit soy in your diet to rule out any possibilities of its
effect on your fertility.