Soy isoflavones
What it is
Phytoestrogens (genistein and daidzein) with weak estrogen receptor activity found abundantly in soybeans, tofu, and miso. The Taku et al. 2012 meta-analysis (and the broader Lethaby 2013 Cochrane review of 43 phytoestrogen trials) found soy isoflavones modestly reduce hot flash frequency, with effect sizes around 20% vs placebo for standardised preparations. Asian populations consuming traditional dietary soy consistently show lower menopause symptoms, osteoporosis rates, and cardiovascular events — but clinical trials with isolated supplements show smaller effects, likely because 50% of Asians vs 25% of Westerners produce equol (a potent daidzein metabolite). Bone density evidence is consistent across trials. Caution in estrogen-receptor positive cancers and thyroid disorders.
Dose
40–80 mg/day isoflavones standardised extract; equol supplements 10 mg/day for non-producers; take with food
Time of day & tips
Not appropriate as sole treatment for severe menopause symptoms. Space at least 4 hours from levothyroxine — competes for absorption. Evidence is stronger for women of East Asian descent. Avoid in estrogen-receptor positive breast or uterine cancer. Consider testing equol producer status if not responding.
Cycling
Safe at food-equivalent doses (40–80 mg/day) with no evidence of harm in women without hormone-sensitive cancers. Long-term use above 150 mg/day not well established.
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