Taking soy dietary supplements also seems to be safe for most people when used short-term (up to six months). Only three intervention studies reported hormonal effects of soy isoflavones in men. It was long thought that soy products were bad for men or that soy's effect on males caused hormonal imbalances. Soy and its influence on breast cancer have long been a source of concern. Consuming soy foods such as soy protein is SAFE. The men were also asked to describe their serving sizes in relation to an average size (i.e. It was long thought that soy products were bad for men or that soy's effect on males caused hormonal imbalances. Out of an abundance of caution, some scientists and dietitians suggest males of all ages should limit soy to an average of no more than 1-2 servings per day. But … Therefore, it’s unlikely that soy is the real culprit. Soy contains phytoestrogens, naturally occurring hormone-like compounds with weak estrogenic effects, which—in the lab—have shown to fuel many cancers. The most common saw palmetto side effects are gastrointestinal issues. If the isoflavones in soy do have a biological effect, most likely young males are most susceptible. Soy Side Effects. These include upset stomach, vomiting, constipation, or diarrhea. The soy foodstuffs included tofu, tempeh, veggie or tofu burgers, miso soup, soy milk, soy ice cream, soy nuts, etc. It can also cause allergic reactions involving rash and itching in some people. Soy can cause some mild side effects such as constipation, bloating, and nausea.  However, in many saw palmetto studies, side effects occurred just as commonly in those taking the placebo as those taking saw palmetto. In particular, high amounts could potentially affect levels of testosterone in men, although research has turned up conflicting results. But there's little evidence this is the case. These data do not support concerns about effects on reproductive hormones and semen quality. It’s tempting to look at these cases and declare soy to at least have the potential to cause unwanted, testosterone-related side effects, but it’s important to apply what we’ve already learned—that phytoestrogens are transient and only affect a limited number of receptors. In fact, quite the opposite. whether they ate more or less than this in each serving). That means the safe amount for boys and teens may be different than of adult men. These recent studies in men consuming soyfoods or supplements containing 40--70 mg/d of soy isoflavones showed few effects on plasma hormones or semen quality. However, concerns in the Western world about the effects on boys and men from eating soy foods have been raised repeatedly and addressed in numerous laboratory and population studies. However, human studies haven't found diets high in soy increase breast cancer risk. However, because isoflavones mimic the effects of estrogen in the body, there are several potential soy side effects in females and males alike to consider as well.