Short-term Effects of Phytoestrogen-rich Diet on Postmenopausal Women

Abstract

Experimental and epidemiologic evidence support the hypothesis that phytoestrogens have both estrogenic and antiestrogenic effects in humans. The authors investigated the effects of short-term (12 weeks) dietary intervention with phytoestrogen-rich diet on menopausal symptoms and serum levels of phytoestrogens and sex hormone-binding globulin (SHBG). One hundred forty-five women with climacteric complaints were assigned randomly to a phytoestrogen-rich diet group or a control group. The phytoestrogen group (n = 78) ate daily portions of phytoestrogen-rich food as a substitute for approximately one fourth of their caloric intake. The test diet consisted of soybean food and flax seeds, both known to contain high concentrations of phytoestrogenic compounds (isoflavones and lignans). The daily intake of phytoestrogen-rich products included tofu, soy drink, miso, and flax seed. The subjects in the control group (n = 36) ate a regular (omnivorous) Israeli diet and did not receive any hormonal treatment. Baseline and end-of-study examinations included: body weight, a subjective assessment of menopausal symptoms using a menopause symptoms questionnaire, determination of serum estradiol, luteinizing hormone, follicle-stimulating hormone, SHGB, and phytoestrogens (enterodiol, enterolactone, equol, daidzein, O-desmethylangolensin, and genistein). The serum levels of phytoestrogens significantly increased in most of the subjects assigned a phytoestrogen-rich diet, whereas the concentrations in the control group remained unchanged. Marked increase in serum levels of SHGB was observed in the phytoestrogen-rich diet group (from 55.8 ± 7.09 nmol/L to 71.2 ± 6.56 nmol/L, p < 0.003) whereas a slight insignificant decrease (from 57.4 ± 9.2 nmol/L to 53.4 ± 8.7 nmol/L) was found in the controls. The total score of menopausal symptomatology was reduced significantly in both groups. There appeared to be an overall greater improvement in the phytoestrogen-rich diet group than in the control group (from 10.65 ± 0.6 to 5.31 ± 0.45 vs. 9.23 ± 0.87 to 4.79 ± 0.71, respectively), but this difference did not reach statistical significance. However, when analyzed separately, the reductions in hot flashes and vaginal dryness scores were more significant (p = 0.004 and 0.005, respectively) in the women assigned a phytoestrogen-rich diet than in the controls. The authors conclude that 12 weeks' partial substitution of omnivorous postmenopausal women with phytoestrogen-rich food increases their serum levels of SHBG. It may alleviate symptoms such as hot flashes and vaginal dryness. Long-term effects on bone density and heart disease remain to be determined.