Biological effects of a diet of soy protein rich in isoflavones on the menstrual cycle of premenopausal women

Author: Cassidy A, Bingham S, Setchell KD
Publication: Am J Clin Nutr. 1994 Sep;60(3):333-40

The low incidence of breast cancer with Japanese and Chinese women, who have a high intake of soya, could be in part explained by the soya isoflavones.

The purpose of this study was to investigate the influence of diet containing soy protein on the hormonal status and regulation of the menstrual cycle. The study was carried out on 6 healthy premenopausal women.

During 1 month, 60 g soya protein, containing 45 mg isoflavones was given to the woman. The soya diet significantly increased follicular phase length and/or delayed menstruation. This diet also surpressed, during midcycle, the levels of luteinizing hormone and follicle-stimulating hormone. other observations were that the plasma estrogen (estradiol) concentrations increased in the follicular phase and cholesterol levels dropped by 9.6%.

The actions of the soya isoflavones are similar to those of tamoxifen, an anti-estrogen drug used as as a prophylactic agent in women at high risk for breast cancer.