Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men.

Soy consumption has been associated with a reduced risk of prostate cancer. The mechanism for this association may involve the effect of soy on the endocrine system. We conducted a randomized dietary intervention study to determine the effects of soy consumption on serum levels of steroid hormones in men. Thirty-five men were randomly assigned to either a soymilk-supplemented group or a control group. The men in the soy-supplemented group were asked to consume 400 ml of soymilk daily for 8 weeks. The men in the control group maintained their usual diet. Blood samples were obtained just before the initiation of the dietary period and thereafter every two weeks for 12 weeks. Changes in hormone concentrations were analyzed and compared between the two groups using the mixed linear regression model against weeks from the start of the dietary period. The mean (SD) soymilk intake estimated from dietary records during the dietary study period was 342.9 (SD, 74.2) ml in the soymilk-supplemented group. There was a significant difference between the two groups in terms of changes in serum estrone concentrations, which tended to decrease in the soy-supplemented group and increase in the control group over time. None of the other hormones measured (estradiol, total and free-testosterone, or sex hormone-binding globulin) showed any statistical difference between the two groups in terms of patterns of change. The results of the study indicate that soymilk consumption may modify circulating estrone concentrations in men.

Hypocholesterolemic effect of soymilk supplementation with usual diet in premenopausal normolipidemic Japanese women.

BACKGROUND: The hypocholesterolemic effect of soy protein concentrates on normolipidemic subjects still remains unclear. Our objective is to assess the effect of soymilk supplementation, a whole soy product, with usual diet on serum lipids in normolipidemic subjects. METHODS: We conducted a randomized controlled trial on 60 premenopausal normolipidemic Japanese women. After excluding 8 subjects whose initial serum concentration of total cholesterol or triacylglycerol was higher than 220 mg/dL (5.69 mmol/L) or 160 mg/dL (1.81 mmol/L), respectively, we encouraged the subjects in the soymilk-supplemented group (n = 27) to consume 400 mL (408 g) of commercial regular soymilk daily during two menstrual cycles. There were no significant differences in variables, including nutrient intake, between the soymilk-supplemented and control (n = 25) groups before the intervention. RESULTS: After the trial, we observed a significant decrease of 10.9 mg/dL, or 5.3%, in serum concentration of total cholesterol in the soymilk-supplemented group. During the intervention, nutrient intake assessment showed significant increases in nutrient densities of vitamin E, polyunsaturated fatty acids, isoflavones, and P/S ratio and decreases in total energy and nutrient densities of vitamin C and green tea in this group. A statistically significant decrease in serum total cholesterol could still be observed even after excluding the estimated hypocholesterolemic effects of soymilk's polyunsaturated fatty acids. CONCLUSIONS: Our results suggest the hypocholesterolemic effect of soymilk, a traditional whole soy product, in Asian countries in normolipidemic subjects.

Effect of soymilk consumption on serum estrogen concentrations in premenopausal Japanese women.

BACKGROUND: Estrogens have been implicated in the development of breast cancer. Preliminary evidence suggests that consumption of soy products, which contain isoflavones (phytoestrogens), can reduce serum estrogen levels. Our purpose was to determine the effect of soy consumption on serum estrogen levels in premenopausal women by use of a dietary intervention approach. METHODS: Premenopausal Japanese women were randomly assigned to receive either a soymilk-supplemented diet (n = 31) or a normal (control) diet (n = 29). The women in the soymilk-supplemented group were asked to consume about 400 mL of soymilk (containing about 109 mg of isoflavones) daily during a study period that involved three consecutive menstrual cycles. Follicular-phase blood samples were to be obtained in the menstrual cycles preceding (cycle 1) and following (cycle 3) the 2-month dietary intervention. All statistical tests were two-sided. RESULTS: At the end of the study period, estrone and estradiol levels were decreased by 23% and 27%, respectively, in the soymilk-supplemented group and were increased by 0.6% and 4%, respectively, in the control group. The changes for each hormone between the two groups were not statistically significantly different. In the soymilk-supplemented group, menstrual cycle length was increased by nearly 2 days, and, in the control group, it was decreased by approximately 1 day, a difference that was not statistically significant. A subgroup analysis restricted to subjects who provided follicular-phase blood samples on the same day or 1 day apart in menstrual cycles 1 and 3 showed a reduction in serum estrone levels in the soymilk-supplemented group that was of borderline statistical significance (P = .07 for change in serum estrone level in soymilk-supplemented group versus control group). CONCLUSION: Much larger studies will be required to confirm the ability of soy products to reduce serum estrogen levels.

Frequent hard physical activity lowered serum beta-carotene level in a population study of a rural city of Japan.

To determine the effect of physical activity on serum beta-carotene, we analyzed data about life styles including 3-day food records and blood samples collected from 57 men and 74 women in a rural city of Japan. Physical activity was asked as mean frequency of hard physical activities per week last year. A declining trend in serum beta-carotene was observed with increasing frequency of hard physical activities in men. In multiple regression analyses, the frequency of hard physical activities showed a negative partial correlation coefficient (r = -0.38, p = 0.007) with serum beta-carotene in men when controlled by age, BMI (body mass index), dietary factors (carotene intake, alcohol consumption and vitamin supplements use), smoking status, serum total cholesterol and serum triglycerides. These results suggest that frequent hard physical activity decreases serum beta-carotene especially in men.