remarked. She hopes to examine bacterial composition differences between low- and high-ITC excretors in more detail in a future study.
Bacterial Metabolism of Daidzein, a Soy Isoflavone
Soy protein has generated long-standing interest for its potential effects on bone loss and hot flashes in perimenopausal women because of the weak estrogenic properties of the two major soy isoflavones, daidzein and genistein. Like many flavonoides, isoflavones are metabolized by gut bacteria.
Daidzein can be metabolized in two ways, via either the formation of equol, which is an isoflavone, or the formation of O-desmethylangolensin. Only about 30 to 50 percent of individuals produce equol, depending on gut microbial composition and depending on the population. For example, in Asia, the percentage of individuals who produce equol is closer to 50 percent, compared to the United States, where it is closer to 25 to 30 percent. Interestingly, Lampe noted, the percentage of individuals in Japan that produce equol appears to be decreasing and is now down to about 30 to 35 percent. It is unknown whether the shift is a result of dietary and associated gut microbiome changes in the younger generation. While not everyone produces equol, most individuals produce O-desmethylangolensin. To determine whether any specific microbial communities are associated with the capacity to produce equol, Hullar and Lampe (unpublished) identified individuals as equol producers or nonproducers based on a soy protein challenge, collected fecal samples, and analyzed 16S rRNA as part of what Lampe described as a “quick and dirty” evaluation of the gut microbiome. Their data suggest that fecal bacterial communities in equol producers differ from those of nonproducers. Moreover, within the equol producers, they found that equol production is associated with differences in the fecal microbiome makeup. Lampe speculated that several different bacteria consortia may be capable of equol production.
A number of research groups have looked at whether equol production is associated with any health outcomes. For example, Aktinson et al. (2003) and Frankenfeld et al. (2004b) reported positive associations between equol production and 2-OH/16alphaOHE1 (16alpha-hydroxyestrone) ratios in premenopausal and postmenopausal women. Frankenfed et al. (2004a) reported that mammographic density was 39 percent lower in equol producers. Akaza et al. (2002) reported that plasma equol concentrations were inversely associated with prostate cancer risk in Japanese men. Lastly, Fuhrman et al. (2008) reported a significant interaction between soy intake and equol-producer status in predicting breast density in postmenopausal women. Lampe noted that not all reported associations hold up across all populations. It is not clear why so many associations have been reported between equol production and disease risk in the Japanese population,