Soy is often thought to be a healthy alternative to other foods. Since soy is a plant-based protein, many assume it's a healthier option. However, certain chemicals contained in the soy plant can impact male fertility.
A man's body doesn't produce pure estrogen. Instead, a small portion of the testosterone that a man produces is converted into estradiol (the male equivalent of testosterone) by the enzyme aromatase. Ideally, this process helps maintain your hormonal balance- it allows for just enough estrogen for your body to keep your brain running and your bones strong, but not enough to interfere with your testosterone levels. When you consume outside estrogen, this delicate balance is thrown off, leading your body to have too much estrogen and too little testosterone.
A healthy level of testosterone is crucial to the production of sperm. It helps maintain a balance of Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH), both of which are need to signal the body to begin producing sperm. Testosterone also helps nurture the baby sperm cells- growing them in to lean, mean baby-making machines. When too much estrogen is consumed and your testosterone plummets, your sperm production slows and your overall sperm quality declines.
Studies are still fairly split as how much soy actually leads to this hormonal imbalance. However, one study found a correlation between lowered sperm counts and men that consumed two or more servings of processed soy (think veggie burgers, tofu, and soy milk products) lost about 41 million sperm/per milliliter from their usual sperm count. Using this as a guideline, keeping your processed soy intake down to one serving or less per day will help keep your hormones balanced and your little swimmers happy and healthy.