While there are some health benefits associated with soy milk and other soy-food products, the hormones found in soy beans can be harmful in large amounts. Soy milk isn't necessarily dangerous to adults, but it should be consumed in moderation, according to Baseline of Health Foundation.
Phytoestrogen is a plant-based estrogen hormone found in high quantities in soy products. Consumed in moderation, it can have positive effects for both men and women, decreasing menopausal symptoms in women and improving prostate health in men. According to Jon Barron at the Baseline of Health Foundation, studies have shown that in helping with menopausal symptoms, soy-derived phytoestrogen was less effective than normal estrogen but more effective than a placebo. Some studies also indicated that a diet that included soy products helped with lowering blood pressure and cholesterol, as well as decreasing the risk of diabetes. While a balance of estrogen is good for humans, eating too much phytoestrogen or drinking too much soy milk can cause estrogen dominance, which may lead to a range of health problems including increased risk of endometrial cancer and breast cancer, increased risk of testicular cancer in men, increased body fat, increased blood clotting and worsening of premenstrual symptoms
Barron also notes that soy beans, like many other foods, contain chemicals called phytates, which block the absorption of nutrients from soy and other foods eaten with the soy. In most plant foods, these chemicals can be neutralized by cooking or soaking the plants, however, in soy it is more difficult to get rid of them; the best way to do this is through fermentation. Because soy milk is not fermented, it has a relatively high amount of phytates. Over-consumption of soy milk may lead to mineral deficiencies.