What this means in practice
Nothing to do. Equol producer status is not something a person can choose or change, testing for it is not part of ordinary care, and the supplement that bypasses the question is not recommended by the menopause society that reviewed it. Anyone eating soy for its own sake can go on doing so without finding out which group they are in.
What people say
Soy only works if you are an equol producer, and most Westerners are not. Get tested, and if you cannot make it, take equol instead.
What the evidence supports
The conversion is real and there is a standard way to measure who does it: a log-transformed urine ratio of equol to daidzein, with a threshold set at minus 1.75. In the study that set that threshold, 59 percent of 29 vegetarians and 25 percent of 12 non-vegetarians were producers, and the vegetarian figure resembles reported frequencies in Japanese adults eating soy. Twelve people is a thin basis for a population estimate, and the widely quoted claim that roughly a quarter to a third of Western adults are producers is consistent with this work rather than demonstrated by it. Equol taken as a supplement does something measurable. Given to 160 postmenopausal Japanese women chosen because they could not make it themselves, 10 mg a day for twelve weeks reduced hot flushes by 1.9 a day against 1.0 on placebo, from a baseline near three a day. The step in between is missing. No source gathered here compares producers with non-producers eating the same soy and measures whether they respond differently. The 2023 North American Menopause Society statement lists equol among the things it does not recommend for hot flushes.
How it is supposed to work
Certain gut bacteria convert daidzein, one of the three isoflavones in soy, into equol. Equol binds oestrogen receptors more strongly than daidzein does, which is the proposed reason people who can make it might get more out of eating soy.
Which way it runs
Strictly one way, and the two are not interchangeable. Gut bacteria turn soy's daidzein into equol; nothing turns equol back into soy isoflavones. When people say soy works better in equol producers, they mean the conversion enhances the response to soy, not that equol enhances soy as an added ingredient.
What is still missing
Every link in the chain has been measured except the one the advice rests on, which is whether being a producer actually changes what soy does for you.
Sources
- Method of defining equol-producer status and its frequency among vegetariansSetchell KD, Cole SJ, 2006
- A natural S-equol supplement alleviates hot flushes and other menopausal symptoms in equol nonproducing postmenopausal Japanese womenAso T et al., 2012
- The 2023 nonhormone therapy position statement of The North American Menopause SocietyThe North American Menopause Society advisory panel (Shufelt CL, Brown V, Carpenter JS et al.), 2023
- Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trialsTaku K et al., 2012