Daidzein can be metabolized to
equol,
dihydrodaidzein (DHD), and
O-desmethylangolensin (ODMA) by intestinal bacteria. Only one third to one half of individuals produce
equol, and evidence exists to support potential
cancer-protective effects of
equol production. We investigated the in vitro metabolism of
daidzein by fecal bacteria and assessed the effect of several
antibiotics on metabolism. Fresh or previously frozen feces from 7
equol producers and 6 nonproducers were incubated with
daidzein, with or without
antibiotics, for 5
d at 37 degrees C. With the exception of one previously frozen sample, fecal inoculates from
equol producers converted
daidzein to
equol. Conversion occurred under anaerobic, but not aerobic conditions. Fecal inoculates from
equol nonproducers did not produce
equol, but some produced ODMA and DHD. Between-subject differences in the effects of
antibiotics on
daidzein metabolism were apparent. Some
antibiotics inhibited the production of
equol but had no effect on DHD production. These results suggest that several bacteria may be involved in
daidzein metabolism, and that they may differ among subjects. This simple in vitro system can facilitate the study of factors influencing
equol production and minimize the need for animal models or human interventions. Furthermore, these analyses can be conducted on fecal samples that have been frozen and stored.