The idea that tofu and other soy products affect male fertility is not new. These foods contain phyto-oestrogens, isoflavones, the plant chemical that mimics the female hormone (oestrogen) and may reduce male hormone (testosterone ) levels in the body. The impact of isoflavones on male fertility has been studied and remains unclear.
In 2008, researchers from the Harvard School of Public Health in Boston found that regular consumption of these foods may lower the sperm count. They studied 99 men from infertile couples.These men were asked to complete a questionnaire that included items on how often, on average, they had eaten each of 15 soy foods listed during the past three months. They were also asked to describe their usual serving sizes compared to an illustration of a medium-size serving.
They found that the men who ate soy foods had, on average, 41 million fewer sperm per ml than men who didn’t eat these foods. But there were no changes seen in the shape of sperm (morphology) or in their ability to swim (motility ) or in the volume of the ejaculate, all of which are important factors in fertility.
The results of this relatively small study are not consistent with the large body of U.S. government and National Institute of Health-sponsored human and research, in which controlled amounts of isoflavones from soy were fed to subjects, with no effect on quantity, quality or motility of sperm.
Besides, it is observed that east Asians have regularly consumed large amounts of soy foods without fertility issues, and they have produced very healthy children for centuries.
Until further large controlled studies are done, there is no harm for you to consume tofu and other soy products.