Soya and fertility...

Soya foods contain phytoestrogens, including isoflavones, which have weak oestrogen-like qualities. Because of this, some people think soya foods can affect male fertility. However, there is no scientific evidence to support this notion. A recent review of all the available research shows that neither soya foods, nor isoflavone supplements from soya, affect testosterone levels in men. This research adds to the large body of evidence supporting the role of soya as part of a healthy veggie diet.

Hamilton-Reeves et al., 2009. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertility and Sterility. 94 (3) 997-1007.