Unlike previous studies investigating the relationship between soy and these menopausal symptoms, the current study included a very large population over a long period of time: more than 1,600 women over 10 years.
The article, titled "Phytoestrogen and Fiber Intakes in Relation to Incident Vasomotor Symptoms: Results from the Study of Women's Health Across the Nation," was published online today in Menopause: The Journal of The North American Menopause Society and will appear in the March 2013 print issue of the journal.
"Given that most women experience unpleasant symptoms, particularly hot flashes and night sweats, during menopause, we were hopeful that certain dietary intakes would provide good alternatives to hormone therapy," said Ellen Gold, lead author of the study and professor and chair of the UC Davis Department of Public Health Sciences. "Unfortunately, based on our study, soy-related foods did not turn out to be the 'magic bullet.'" The study analyzed data from the Study of Women's Health Across the Nation (SWAN), which followed more than 3,000 premenopausal and early perimenopausal women with annual visits for 10 years. Women answered detailed questionnaires of their dietary habits at baseline, year five and year nine, and in each year were asked about the frequency of various menopausal symptoms, including hot flashes and night sweats.
The new study focused on the 1,651 women who had not yet had hot flashes and night sweats (called vasomotor symptoms) at the beginning of the study, because the investigators wanted to specifically evaluate the effect of dietary factors on preventing the onset of these symptoms. The main dietary factor of interest in this study was phytoestrogens, also known as plant-based estrogens. Predominantly found in tofu, soy milk and other soy-containing foods, phytoestrogens have a chemical structure similar to estrogen and are believed to mimic the effects of the female hormone in the body. Since estrogen levels drop during menopause, the investigators hypothesized that a diet high in phytoestrogens would reduce menopause symptoms. They also evaluated the participants' consumption of fiber, because it is thought to increase the availability of estrogens in the body.