Urinary Isoflavone Excretion and Soy Consumption in Three Generations of Japanese Women in Hawaii

Abstract

Isoflavone (IFL) bioavailability and metabolism may differ depending on lifetime exposure to soy foods. 43 Japanese women in Hawaii ages 18–78 years belonging to families of two to three generations collected an overnight baseline urine sample followed by a second overnight urine sample after consumption of a serving of soymilk. A participant was considered first generation (1G) if she was over age 60, second generation (2G) if she was age 30–59, and third generation (3G) if she was under age 30. IFL intakes during the last year were estimated using a 12-item soy food-frequency and a lifetime soy consumption questionnaire, and published nutritional databases. Urinary isoflavone excretion (UIE) of daidzein, genistein, and equol was determined by LC/MS. Most popular soy foods were, miso soup and green soybeans. The mean self-reported intake of dietary soy isoflavones for all participants was 11.5 mg/day (±12.8). The highest mean IFL intake was observed by 2G, followed by 1G and lastly by 3G. UIE at baseline was highest for 1G followed by 2G and lastly by 3G. After intervention 3G had the highest mean UIE, followed by 1G, and lastly 2G. 1G excreted the greatest amount of equol, while the other generations showed trace amounts. This suggests that 1G is exposed habitually to greatest amounts of IFL and metabolizes them differently from the other generations.