Isoflavone Research Initiative

The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.

The safety of isoflavones in the breast was the topic of the presentation of Prof. Gertrud Maskarinec (Cancer Research Center of Hawai’i) (Maskarinec et al. 2010). Maskarinec examined the effect of isoflavones on the production of nipple aspirate fluid (NAF) as a possible indicator of breast cancer risk, and on urinary estrogen metabolites, i.e., the ratio of 2:16α-OH-estrone.

Only women without a history of breast cancer producing at least 10 µl of NAF were included. 96 women were randomized to a cross-over experiment involving high or low soy diet for six months, followed by a 1 month wash-out period before crossing over to the alternative study arm. High soy diet consisted of soy food delivering at least 50 mg of isoflavones/day. 14 women dropped out of the study, and 82 women completed both diets. 26 % of the study participants were of Asian ethnic origin, however, all of them were third-generation Americans with typical American diet. Asians with high dietary consumption of soy food could not participate in the trial, as their baseline values would have distorted the findings.

The observations regarding the volume of NAF were difficult to interpret, mostly because this parameter was found not to be a highly reliable factor due to the intra- and interindividual variations and problems related to the technique of measurement. The results showed an increase of NAF volumes associated with high soy diet (p = 0.03), which is basically considered a protective effect.

The findings with the estrone metabolite ratio were, however, more obvious: isoflavones contributed to an improvement of the metabolic ratio of 2- to 16α-hydroxy-estrone, which should translate in cancer protective effects. In the total group the comparison of high versus low soy was borderline significant (n = 80, p = 0.056). The effect was mainly caused by an increased formation of 2-OH estrone, which confirmed similar observations (Teas et al. 2009). An increased formation of 2-OH estrone and the corresponding improvement of the 2:16α-OH estrone ratio is considered a cancer preventive factor.

References

Maskarinec G, Morimoto Y, Conroy S, Nordt FJ and Franke A (2010). Nipple aspirate fluids and estrogen metabolites during a 6-month soyfood intervention. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.

Teas J, Hurley TG, Hebert JR, Franke AA, Sepkovic DW and Kurzer MS (2009). Dietary seaweed modifies estrogen and phytoestrogen metabolism in healthy postmenopausal women. J Nutr 139(5):939-944.