Urinary isoflavonoid and lignan excretion on a Western diet: Relation to soy, vegetable, and fruit intake

Dietary isoflavone and lignan phytoestrogens are potential chemopreventive agents. This has led to a need to monitor exposure to these compounds in hu man populations and to determine which components of a mixed diet contribut e to the exposure. Typically, urinary isoflavonoid excretion is associated with soy consumption and that of lignans is associated with whole grains. H owever, other plant foods are known to contain phytoestrogen precursors. Th e purpose of this study was to examine the association between urinary isof lavonoid and lignan excretion and intakes of vegetables and fruits (V&F). I soflavonoids (genistein, daidzein, O-desmethylangolensin, and equol) and li gnans (enterolactone, enterodiol, and matairesinol) were measured in urine collected for 3 days from 49 male and 49 female volunteers (age, 18-37 year s) reporting a wide range of habitual V&F intakes. Dietary intakes were ass essed using 5-day diet records and a food frequency questionnaire. V&F grou pings (total V&F, total V, total F, soyfoods, and V&F grouped by botanical families) were used to assess the relationship between V&F intake and urina ry isoflavonoid and lignan excretion. Pearson correlations were performed. Intake of soyfoods was correlated significantly with urinary genistein (r = 0.40; P = 0.0001), O-desmethylangolensin (r = 0.37; P = 0.0002), daidzein (r = 0.34; P = 0.0007), and the sum of isoflavonoids (r = 0.39; P = 0.0001) . There was no association between equol excretion and soy intake or betwee n the isoflavonoids and any other V&F groupings. In addition, isoflavonoid excretion was correlated positively with intake of high-fat and processed m eats, particularly among men who did not consume soy. This suggests that, e ven in the United States, on a Western diet, soyfoods are the primary contr ibutors to isoflavone intake; however, additional "hidden sources" of soy m ay also contribute to exposure. In contrast, a variety of fiber-containing foods contributed to lignan excretion; the sum of the urinary lignans, ente rodiol, enterolactone, and matairesinol, was associated with intake of tota l F (r = 0.27; P = 0.008), total V&F (r = 0.25; P = 0.01), soyfoods (r = 0. 28; P = 0.006), and dietary fiber (r 0.36; P = 0.0003). Overall, urinary ph ytoestrogens (isoflavonoids + lignans) were significantly higher in "high" compared with "low" V&F consumers. Compared with the "low" V&F group, the " high" group consumed diets that were, on average, higher in fiber and carbo hydrate and soyfoods and lower in fat; thus, the urinary phytoestrogens may also be a useful marker of healthier dietary patterns.