Men who eat just half a serving of soya foods (e.g. miso, tofu and tempeh) a day may have drastically fewer sperm than those who do not consume such foods. Harvard researchers asked 100 couples seeking therapy for infertility about their intake of 15 soy-based foods over the preceding three months. An analysis of the data revealed that those men who consumed soy daily had sperm counts averaging 65 million sperm per milliliter, 40% less than the normal sperm count of 80 to 120 million sperm per mL. Men with counts lower than 20 million sperm per mL are generally considered infertile.
Soy contains high levels of estrogen mimicking isoflavones, which could affect a man's fertility.
The good news for those with infertility is that it can often be very effectively treated naturally (see Effective Natural Therapy for Infertility ).