Urinary isoflavonoid excretion and soy consumption in three generations of Japanese women in Hawaii

Abstract

To explore soy intake and urinary isoflavonoid excretion within several generations of American-Japanese women based on the hypothesis that earlier generations excrete higher levels of urinary isoflavonoids, in particular the metabolite equol, than later generations. A convenience sample of 43 women from 19 families aged 18-78 years, all of whom reported at least 50% Japanese ancestry. Each woman collected overnight urine samples at baseline and after consuming one serving of soymilk, both samples were analyzed for the isoflavonoids daidzein, genistein and equol using liquid chromatography-mass spectrometry. Median isoflavone intakes during the last year were 7.2 mg/day for the first generation, 7.3 mg/day for the second generation and 6.3 mg/day for the third generation (P=0.36). At baseline, the median isoflavonoid excretion for the first generation was nonsignificantly higher than for later generations (190, 86 and 42 nmol/h; P=0.20) but after intervention, the median urinary isoflavonoid excretion was very similar for the three groups: 2465, 1895 and 2775 nmol/h (P=0.70). Following intervention, a nonsignificantly higher proportion of older than younger women (53 vs 32 and 33%; P=0.41) excreted the metabolite equol. The respective median equol excretion rates by generation following intervention were 39.5, 4.2 and 3.5 nmol/h (P=0.04). This small investigation among three generations of Japanese-Americans detected a higher equol production among older women after a soy challenge, but no difference in the excretion of total isoflavonoids after a standardized dose of soymilk was observed.