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Isoflavones

Polyphenols

Polyphenols specific to soy and a few legumes, similar in shape to estrogens.

It is the clearest example of the fact that the same food is not worth the same thing to two people.

Effects and benefits

The molecules of soy faintly resemble estrogens, and it shows at menopause: in meta-analyses of trials, about fifty milligrams a day reduced hot flashes by about a fifth more than a placebo. In some people, bacteria make them even more active.

Genistein and daidzein bind to estrogen receptors, especially the beta receptor, a hundred to a thousand times more weakly than the hormone. They are called phytoestrogens, but their effect depends on the tissue: they can slightly mimic, or slightly curb, the hormone.

A meta-analysis of nineteen trials put a figure on the effect on hot flashes: 54 mg of isoflavones a day reduce their frequency by about 20% more than a placebo, and their intensity by about 26% (Taku et al., 2012). The effect takes several weeks to appear.

By sex and age: the interest is mainly for women at menopause. For EFSA, isoflavone supplements have shown no harmful effect on the breast, uterus or thyroid of postmenopausal women at the doses studied (EFSA, 2015). French authorities, however, advise against them during pregnancy and in children (AFSSA, 2005). A serving of tofu provides 20 to 40 mg.

Slackia and Adlercreutzia turn daidzein into equol, and only 25 to 30% of Westerners can do it, versus 50 to 60% in East Asia. Many of the effects attributed to soy in fact concern only equol producers.

Sources: Taku et al., Menopause, 2012 · EFSA, 2015 · AFSSA, 2005

Where to find it (9)

Also, in smaller amounts (7)