Eating more soy was associated with larger reductions in menopausal vasomotor symptoms (VMS), such as hot flashes, among U.S. women that can convert soy to a compound called equol, according to data from a first-of-its-kind study presented in an oral session at the North American Menopause Society (NAMS) 2012 annual meeting.
"Numerous studies have examined the association between soy isoflavones–from both soy foods and supplements–and menopausal VMS, but with mixed results," said Belinda H. Jenks, Ph.D., director of Scientific Affairs & Nutrition Education at Pharmavite LLC., which funded the prospective observational study. "However, they do not routinely account for whether the enrolled women can produce equol, which has documented reductions on certain VMS such as hot flashes."
The study, conducted by researchers at the Group Health Research Institute, University of Washington and the Fred Hutchinson Cancer Institute, is the first to examine equol production status and the effect of varied soy consumption on VMS in menopausal U.S. women. Evidence from prior observational studies suggests that Japanese women have milder menopausal symptoms in those who are equol producers compared to nonproducers. Additional peer-reviewed studies have documented that dietary supplements containing equol have reduced VMS symptoms in postmenopausal women who are not equol producers.
Equol is produced from the natural metabolism, or conversion, of daidzein, an isoflavone found in whole soybeans. Not everyone can produce equol after soy consumption, as the production depends on the types of bacteria present in the large intestine. About 50 percent of Asians and 20 to 30 percent of North Americans and Europeans, who in general consume less soy than Asians, have the ability to produce equol.
NAMS study quantifies VMS reduction in U.S. equol producers
Consuming higher levels of soy containing daidzein was associated with fewer VMS, but only among the women who were equol producers.
Among the 129 equol producers, 36 percent of the study's 355 participants, those consuming the most daidzein in their daily diet, versus those with the least daidzein, were 76 percent more likely to have fewer than the study's daily average number of VMS, 2.33. The positive trend in the equol producers between increased daidzein consumption and reduced VMS symptoms occurred across all four intake levels of daidzein (p=0.06). In comparison, no associations between daidzein intake and VMS were observed in the 229 equol nonproducers.
Investigators grouped all of the women into four levels of soy consumption. The four equol producer groups averaged 28.55, 14.2, 9.01 and 4.88 milligrams of daidzein per day (mg/d) and the average daidzein intake levels in the equol nonproducers were 28.69, 13.76, 8.98 and 4.63 mg/d, which is a range comparable to general soy consumption in Asians.
The researchers also used the Soy-Food Questionnaire to ask women about their diets. This validated tool, developed by Fred Hutchinson Cancer Research Center, poses questions about the consumption of 20 commonly eaten soy foods and supplements to assess soy intake among postmenopausal women in the United States.
The enrolled women averaged 53 years and more than 60 percent were postmenopausal.
Otsuka Pharmaceutical Co. Ltd. supported the study. The complete data will be submitted to a peer-review journal for publication.