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

OBJECTIVE: 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. SUBJECTS: A convenience sample of 43 women from 19 families aged 18-78 years, all of whom reported at least 50% Japanese ancestry. INTERVENTIONS: 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. RESULTS: 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). CONCLUSIONS: 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.

Serum prostate-specific antigen but not testosterone levels decrease in a randomized soy intervention among men.

BACKGROUND: Low prostate cancer incidence and high soy intake in Asian countries suggest a possible protective effect of soy foods against prostate cancer. The goal of this pilot study was to evaluate the feasibility of a randomized, crossover soy trial among men and to investigate the effects of daily soy intake on serum prostate-specific antigen (PSA) and testosterone levels. METHODS: We randomized 24 men to a high or a low soy diet for 3 months. After a 1-month washout period, the men crossed over to the other treatment. During the high soy diet, the men consumed two daily soy servings; during the low soy diet, they maintained their usual diet. During the entire study each man donated four blood samples and five overnight urine samples. Dietary compliance was assessed by soy calendars, 24-h dietary recalls, and urinary isoflavone excretion measured by high-pressure liquid chromatography with photodiode array detection. Blood samples were analyzed for serum testosterone and PSA by radioimmunoassay. When necessary, variables were log transformed. Two sample t-tests compared the two groups before each study period. Mixed models incorporating the repeated measurements were used to evaluate the effect of the soy diet on urinary isoflavone excretion and serum analytes. RESULTS: Twenty-three men aged 58.7+/-7.2 years completed the study. The compliance with the study regimen was high according to self-reported soy food intake and urinary isoflavone excretion. No significant between-group and within-group differences were detected. During the high soy diet, dietary isoflavone intake and urinary isoflavone excretion increased significantly as compared to the low soy diet. A 14% decline in serum PSA levels (P=0.10), but no change in testosterone (P=0.70), was observed during the high soy diet in contrast to the low soy diet. CONCLUSION: The high adherence as shown by three measures of compliance in this pilot trial demonstrated the feasibility of an intervention based on soy foods among free-living men.

Urinary isoflavone excretion as a compliance measure in a soy intervention among young girls: a pilot study.

OBJECTIVE: To investigate the compliance of young girls with a soy intervention. DESIGN: An 8-week dietary intervention and urine sample collection. SETTING: Free-living girls. SUBJECTS: A convenience sample of 8- to 14-y-old girls (20 started and 17 finished the study) recruited through flyers distributed to staff members and previous study participants. INTERVENTION: The girls consumed one daily serving of soymilk, soy nuts, or tofu, completed 3-day food records, kept daily soy intake logs, and collected weekly urine samples. MAIN OUTCOME MEASURES: Compliance with the intervention was evaluated by daily soy intake logs, 3-day food records analyzed by the center's Food Composition and Food Groups Servings Databases, and weekly urinary isoflavone excretion using high-pressure liquid chromatography. The statistical analysis included paired t-tests, analysis of variance, and Spearman's rank-order correlation coefficients. RESULTS: Daily soy intake logs indicated a mean intake of 6.28 servings out of a maximum of 7.0 servings per week. The food records revealed a six-fold increase in isoflavone intake during the study period (P<0.01) which was confirmed by an increase in urinary isoflavone excretion of similar magnitude (23.3-142.1 nmol/mg creatinine, P=0.02). CONCLUSIONS: This study demonstrated the ability of young girls to consume one daily soy serving and the usefulness of urinary isoflavones as a primary compliance measure. The high urinary isoflavone excretion levels detected in girls as compared to adult women suggest less intestinal degradation and/or greater absorption of isoflavones in nonadult populations. This finding requires further investigations into the pharmacokinetics of isoflavones.

Nutritional changes among premenopausal women undertaking a soya based dietary intervention study in Hawaii.

BACKGROUND: We conducted a 2-year nutritional intervention among premenopausal women. The goal was to incorporate two daily servings of soya into the regular diet. This report describes the dietary modifications and assesses their nutritional adequacy with regard to major nutrients. METHODS: In this analysis of 100 intervention and 106 control subjects, women completed a validated food-frequency questionnaire at baseline; throughout the study, they participated in at least three unannounced 24-h recalls. RESULTS: At randomization, both groups were similar in age and body weight, reported low soya intake, and did not differ by intake of major nutrients and foods. According to the 24-h recalls, women in the intervention group consumed nearly two servings of soya per day, while the control women remained at 0.2 servings. In comparison with the control group, the intervention group consumed fewer dairy products, primarily milk, but also less meat, nuts and seeds. As a result of the dietary modification, the intervention women consumed less-saturated fat and cholesterol and more protein, dietary fibre, calcium and vitamins than the control group. CONCLUSION: These results suggest that women in the intervention group improved the overall quality of their diet by adding two servings of soya per day.