The new large scale study, led by US scientists at the University of California Davis, finds that a diet rich in products such as soy milk and tofu does not prevent the onset of hot flushes and night sweats as women enter menopause.
Writing in Menopause, the researchers investigated whether consumption of a soy-rich diet prevented the onset of vasomotor symptoms (VMS – such as hot flushes and night sweats). However, the data collected from more than 1,600 women over 10 years found no association between soy intake levels and such prevention of onset.
"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 Professor Ellen Gold, lead author of the research.
"Unfortunately, based on our study, soy-related foods did not turn out to be the 'magic bullet,'" she said.
Gold said the results of the study contribute to the discussion about the effects of phytoestrogens on symptoms at menopause, but said the finding ‘is not the final word.’
“Other advantages to these compounds may exist, or it may be that a subset of women will benefit from phytoestrogen intake because of their genetic makeup, which could affect their metabolism of these dietary factors,” she suggested.
Chiefly found in tofu, soy milk and other soy-containing foods, phytoestrogens have a chemical structure similar to oestrogen, and have been suggested to mimic the effects of the female hormone in the body.
Since oestrogen levels drop during menopause, many researchers have suggested that a diet high in phytoestrogens could reduce menopause symptoms.
"In general, women of Asian ancestry report fewer menopausal hot flashes than do women of European backgrounds," said Gail Greendale, who also worked on the study. "The 'Eastern' dietary pattern, which is high in phytoestrogens, has been one of the proposed explanations for the ethnic differences in hot flash occurrence.
“Our findings do not support the theory that higher phytonutrient intakes are associated with lower hot flash rates."
The researchers noted that although other studies have examined similar ideas, the outcomes have been inconsistent: “Although reduction of vasomotor symptoms has been reported in postmenopausal women … a clear dose response has not been shown, has largely not been reported for perimenopausal women, and has largely only been reported for reducing prevalent VMS, not preventing newly developing VMS.”
Gold and her team said unlike previous studies to investigate the relationship between soy and these menopausal symptoms, their new research included a very large population over a long period of time – analysing data from the Study of Women's Health Across the Nation (SWAN).
The study focused on the 1,651 women from the SWAN study who had not yet had hot flushes and night sweats at the beginning of the study. The women answered detailed questionnaires on 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, they explained.
No consistent correlations were found between dietary phytoestrogens or fibre and the onset of menopausal symptoms in women who were not yet postmenopausal when they started the study.
Gold and her team conclude that in order to ascertain whether dietary phytoestrogens have an effect on the prevention of hot flushes for certain, “a randomised, placebo-controlled, double-masked trial with sufficient numbers of women in different racial/ethnic, menopausal status, and metabolic groups over years of follow-up is required.”
“But our results suggest that a clinically significant or large effect is improbable.”
Source: Menopause: The Journal of The North American Menopause Society
Published online ahead of print, doi: 10.1097/gme.0b013e31826d2f43
“Phytoestrogen and fiber intakes in relation to incident vasomotor symptoms: results from the Study of Women's Health Across the Nation”
Authors: E.B Gold, K. Leung, S.L. Crawford, M-H. Huang, E.L Waetjen, G.A. Greendale