Effects of a high-fiber, low-fat diet intervention on serum concentrations of reproductive steroid hormones in women with a history of breast cancer

Purpose: Diet intervention trials are testing whether postdiagnosis dietary modification can influence breast cancer recurrence and survival. One possible mechanism is an effect on reproductive steroid hormones. Participants and Methods: Serum reproductive steroid hormones were measured at enrollment and 1 year in 291 women with a history of breast cancer who were enrolled onto a randomized, controlled diet intervention trial. Dietary goals for the intervention group were increased fiber, vegetable, and fruit intakes and reduced fat intake. Estradiol, bioavailable estradiol, estrone, estrone sulfate, androstenedione, testosterone, dehydroepiandrosterone sulfate, follicle-stimulating hormone, and sex hormone-binding globulin were measured. Results: The intervention (but not the comparison) group reported a significantly lower intake of energy from fat (21% v 28%), and higher intake of fiber (29 g/d v 22 g/d), at 1-year follow-up (P < .001). Significant weight loss did not occur in either group. A significant difference in the change in bioavailable estradiol concentration from baseline to 1 year in the intervention (-13 pmol/U versus the comparison (+3 pmol/L) group was observed (P < .05). Change in fiber (but not fat) intake was significantly and independently related to change in serum bioavailable estradiol (P < .01) and total estradiol (P < .05) concentrations. Conclusion: Results from this study indicate that a high-fiber, low-fat diet intervention is associated with reduced serum bioavailable estradiol concentration in women diagnosed with breast cancer, the majority of whom did not exhibit weight loss. Increased fiber intake was independently related to the reduction in serum estradiol concentration.