lignans and isoflavanone

We have investigated the metabolism of isoflavones and lignans in germ-free (GF) rats and rats associated with human faecal bacteria (human flora associated [HFA] rats), in order to provide unequivocal evidence for the role of the gut microflora in the absorption and metabolism of these phytoestrogens. Furthermore, we have investigated whether certain metabolic characteristics (high equol-producing and low equol-producing status) of human intestinal floras can be transferred to GF rats. Germ-free rats fed a soy-isoflavone containing diet excreted large quantities of daidzein and genistein in urine indicating that the gut microflora is not required for the absorption of isoflavones. The isoflavone metabolites equol, O-desmethylangolensin and the lignan enterolactone were not detectable in urine from the GF rats, but were present in HFA rat urine, indicating that they were products of gut microflora activity. Colonization of GF rats with a faecal flora from a human subject with the capacity to convert daidzein to equol, resulted in the rats excreting substantial amounts of the metabolite. In contrast, equol was undetectable in urine of HFA rats associated with a faecal flora from a low equol-producing subject. The results therefore show that the inability of some subjects to produce equol is a consequence of the lack of specific components of the gut microflora.

Topics: Animals; Chromans; Digestive System; Digestive System Physiological Phenomena; Equol; Estrogens, Non-Steroidal; Feces; Female; Germ-Free Life; Humans; Isoflavones; Lignans; Male; Rats; Rats, Inbred F344

Diets rich in naturally occurring plant estrogens (phytoestrogens) are strongly associated with a decreased risk for cancer and heart disease in humans. Phytoestrogens have estrogenic and, in some cases, antiestrogenic and antiandrogenic properties, and may contribute to the protective effect of some diets. However, little information is available about the levels of these phytoestrogens in the general US population. Therefore, levels of phytoestrogens were determined in urine (N=199) and serum (N=208) samples taken from a nonrepresentative subset of adults who participated in NHANES III, 1988-1994. The phytoestrogens quantified were the lignans (enterolactone, enterodiol, matairesinol); the isoflavones (genistein, daidzein, equol, O-desmethylangolensin); and coumestrol (urine only). Phytoestrogens with the highest mean urinary levels were enterolactone (512 ng/ml), daidzein (317 ng/ml), and genistein (129 ng/ml). In serum, the concentrations were much less and the relative order was reversed, with genistein having the highest mean level (4.7 ng/ml), followed by daidzein (3.9 ng/ml) and enterolactone (3.6 ng/ml). Highly significant correlations of phytoestrogen levels in urine and serum samples from the same persons were observed for enterolactone, enterodiol, genistein, and daidzein. Determination of phytoestrogen concentrations in large study populations will give a better insight into the actual dietary exposure to these biologically active compounds in the US population.

Topics: Adult; Diet; Estrogens; Estrogens, Non-Steroidal; Ethnicity; Female; Humans; Isoflavones; Lignans; Male; Middle Aged; Nutrition Surveys; Phytoestrogens; Plant Preparations; United States