The effects of soy protein and probiotics on isoflavone and hormone metabolism in postmenopausal breast cancer survivors and women with no cancer history

The purpose of this thesis was to evaluate the effects of soy protein and probiotic consumption on phytoestrogen and reproductive hormone metabolism in 20 healthy postmenopausal women who had been successfully treated for breast cancer (survivors) and 20 women who had no personal or family history of the disease (controls).; Soy consumption significantly increased phytoestrogen concentrations. Controls had higher plasma concentrations of genistein and enterolactone but lower O-desmethylangolensin (O-dma) than survivors. Overall, probiotic consumption did not significantly affect plasma phytoestrogen concentrations, although O-dma tended to be lower when probiotics and soy were consumed together. Despite that equol producer frequency was unaffected by probiotic supplementation, two subjects, plasma equol concentrations changed substantially with probiotic consumption.; Plasma reproductive hormones were not affected by soy or probiotic consumption and effects were not different between controls and survivors. However, consumption of soy protein significantly decreased sex hormone-binding globulin. While this decrease was statistically significant, its clinical significance is uncertain. Interestingly, when concentrations were averaged across all diets, survivors had significantly lower FSH and trends toward lower androstenedione and estrone-sulfate.; At baseline, survivors tended to have a lower 2-hydroxyestrogen (2OHE) to 16α-hydroxyestrone (16OHE₁) ratio (2:16OHE₁) than controls. During the study, soy consumption tended to increase 2OHE and 16OHE₁ excretion. Most interestingly, the effects of soy consumption significantly differed between subjects with high and low plasma equol concentrations, with soy significantly increasing 2OHE excretion and the 2:16OHE₁ ratio in the high equol group but not altering either endpoint in the low equol group. Probiotics did not independently affect estrogen metabolism nor alter the effects of soy.; In conclusion, these findings suggest that while these particular probiotic bacteria may have modestly altered phytoestrogen metabolism, they did not enhance the effects of soy as hypothesized. The independent effects of soy on hormone metabolism were small, but data suggest that equol producer status may have a significant impact on the effects of soy consumption. Lastly, the observed differences in phytoestrogen and hormone metabolism between breast cancer survivors and women with no cancer history may enhance future research on the role of phytoestrogens and hormones in breast cancer etiology.