Soy
The results of soy products for treating menopausal symptoms in clinical trials have generally been mixed, although several trials have shown an improvement in level of hot flashes (Nahas 2007, Cheng 2007). Newer met-analysis level data has shown modest reduction in hot flash severity and frequency and decreased severity of vagina dryness (Franco 2016)
Because soy has a weekly estrogenic effect, there have been worries about soy inducing primary or secondary malignancies in susceptible women. Research shows that reasonable doses of soy foods (not necessarily supplements) are likely safe.
Background Information:
Isoflavones are the most estrogenic of the compounds found in soy, at a level of one to two milligrams per gram of soy protein.
Genistein is the most common isoflavone in soy.
Soy can increase endometrial hyperplasia.
There is no convincing evidence that soy foods (tofu, edamame, etc.) are dangerous in breast cancer survivors.
At very high doses, theoretical anti-thyroid effects may occur.
Intake of 30 to 40 milligrams of soy isoflavones per day (1 to 1½ servings) is similar to the intake in Asian cultures and is likely safe, even in breast cancer survivors.
Some evidence suggests that higher doses, near 100 milligrams per day of isoflavones are more effective in reducing hot flashes. This would need to be in soy food form and not supplement form for breast cancer survivors.
Some interesting data exists on whether being able to produce equol from isoflavones enhances the ability of the soy to have estrogenic effects. According to Asian studies, only some women have the ability to break down soy in digestion to equol. Women with this capability had better physical parameters (such as lower blood pressure and less bone loss) in randomized studies (Tomala 2007, Wu 2007). Further studies are needed to better characterize this effect.