Soy isoflavones are phytoestrogens (similar natural estrogen compounds), used to reduce menopausal symptoms and to offer a natural alternative to hormone replacement therapy. A recent meta-analysis concludes that phytoestrogens, such as soy isoflavones, do not present risks to heart health and breast cancer.
The new meta-analysis focused on all isoflavones, including 92 randomized controlled trials with 9629 participants. In it, components such as genistein, naringenin, kaempferol and lignans, were not related to a higher incidence of adverse events.
Comparison of phytoestrogen groups with placebo or the control group, showed that the incidence of side effects was approximately the same, with 36.7 and 38 percent, respectively . Although there were higher rates of gastrointestinal side effects in users of phytoestrogens, no significant differences were observed in relation to gynecological, musculoskeletal, or neurological side effects. In addition, rates of hormone-related side effects, including breast cancer and endometrial cancer, were not significantly different between the groups.
These results provide peace of mind to women seeking safe and natural alternatives to hormone replacement therapies, as previous conflicting reports had linked the use of soy isoflavones with the stimulation of Breast cancer cells in mice, although population studies had shown that women on a diet high in soybeans generally have lower rates of breast cancer.
Reference: “Side Effects of Phytoestrogens: A Meta-analysis of Randomized Trials” The American Journal of Medicine October 2009, Volume 122, Issue 10, Pages 939-946. C.B. Tempfer, G. Froese, G. Heinze, E.-K. Bentz, L.A. Hefler, J.C. Huber