Equol (4',7-isoflavandiol) is a secondary metabolite that is produced from the isoflavon daidzein by bacteria of the gut flora. Until now, it is not clear, which strains of bacteria are responsible for the synthesis of equol. Probably Streptococcus, Lactic Acid Bacteria (LAB) and Bifidobacterium are involved.

Equol formation in the intestine

Only about one third (Caucasian population) to half (Japanese) of the people can metabolize equol from daidzein. The reason appears to be a different population of intestinal bacteria. A high fat intake has a negative impact on the formation of equol, too.

In people, who are able to synthesize equol, the cholesterol-decreasing and anti-inflammatory effect of a soy-rich diet is higher than in people, who can not build this secondary metabolite.

After the intake of daidzein-rich foods such as soy, equol is present in blood and urine. It has a mild estrogen activity (0.1% of the steroid-estrogens) and can bind to both estrogen receptors ERα and ERβ (daidzein only ERβ). Thus, equol has a greater biological effect than daidzein.

Equol stimulates SHBG

In vitro (in a test tube), equol stimulates the sex hormone-binding globulin (SHBG). It is a protein produced by the liver cells that binds to sex hormones (e.g. estrogen, testosterone) in the bloodstream. The higher the concentration of SHBG, the more sex hormones are bound and biologically inactive.

It was found that patients with breast cancer have the lowest SHBG concentrations in blood plasma and the lowest excretion of equol. Therefore, a correlation between breast cancer and the formation and metabolism of equol could exist.

A similar effect could explain the possible protection of equol against prostate cancer. Free circulating DHT (5α-Dihydrotestosterone) - a descendant of the male sex hormone testosterone - stimulates the growth of the prostate. A stronger binding to SHBG, again, may decrease the biological activity of DHT.

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