The jury is still out on the health effects of soy and its attendant endocrine-bending isoflavones; some experts point to its association with decreased prostate cancer and others toward its link to decreased fertility in animal studies. Well, you may want to think twice before stocking the fridge with soy milk. Some evidence suggests that at high levels the plant-based estrogens in soy can disrupt the ovarian cycle. And according to a Harvard study of 99 men from an infertility clinic, those who knocked back the most soy products also had the lowest sperm count: 41 million sperm per milliliter fewer than men who didn't consume soy. That's one-half to one-third of the normal sperm count (80 to 120 million sperm per milliliter).
Source: "Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic," Human Reproduction