Usual dietary consumption of soy foods and its correlation with the excretion rate of isoflavonoids in overnight urine samples among Chinese women inShanghai

Soy foods and certain soy constituents, particularly isoflavones, have been suggested to have potential cancer-inhibitory effects in laboratory and ep idemiological studies. Chinese women in Shanghai consume high levels of soy foods and have low incidence rates of breast and other hormone-related can cers. To assess the usual dietary consumption of soy foods and evaluate the correlation of soy food consumption with the urinary excretion of isoflavo noids in overnight urine samples in this population, we analyzed data from 60 healthy women included in art ongoing population-based case-control stud y of breast cancer in Shanghai. Usual consumption of soy foods in the previ ous five-year period was assessed using a food-frequency questionnaire, and urinary excretion of daidzein, genistein, glycitein, equol, and O-desmethy langolensin was measured from overnight urine samples collected at the time of dietary assessment. Virtually all women (96.7%) in Shanghai consumed so y foods at least once a week. The median intake of soy food was 100.6 g/day , with 25th and 75th percentiles of 36.8 and 238.2 g, respectively. The med ian intake of isoflavones was 39.26 mg/day, and there was a nearly fourfold difference between the 25th and 75th percentiles of this measurement. With the increasing intake of soy foods, urinary excretion rates of total isofl avonoids and all individual major isoflavonoids were increased in a dose-re sponse manner (trend test p less than or equal to 0.05). At individual leve ls the urinary excretion rate of total isoflavonoids was correlated closely with dietary soy food intake, with a correlation coefficient of around 0.5 (p < 0.001). These results indicate that the urinary excretion rate of tot al isoflavonoids measured from overnight urine samples may reflect reasonab ly well the usual intake of soy foods in a population with a high level of soy food consumption.