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A randomized controlled trial of the effect of dietary soy and flaxseed muffins on quality of life and hot flashes during menopause

Lewis, Jacqueline E. MD1; Nickell, Leslie A. MD2; Thompson, Lilian U. PhD3; Szalai, John P. PhD4; Kiss, Alex PhD5; Hilditch, John R. MD2

doi: 10.1097/01.gme.0000191882.59799.67

Objective: To compare the effects of daily ingestion of soy flour (S), ground flaxseed (F), or wheat flour (W) muffins, on quality of life and hot flash frequency and severity in postmenopausal women.

Design: This was a double-blind, randomized, controlled, intention-to-treat trial. Ninety-nine women, 1 to 8 years after menopause, ingested muffins with 25 g of flaxseed (50 mg of lignans), 25 g of soy (42 mg of isoflavones), or wheat (control) daily for 16 weeks. Subjects completed the Menopause-specific Quality of Life instrument monthly along with daily hot flash frequency and severity diaries. Compliance measures included a 3-day food diary and urinary isoflavone and lignan analyses at weeks 0 and 16 and returned muffin counts monthly.

Results: Eighty-seven women (28, ground flaxseed muffins; 31, soy flour muffins; and 28, wheat flour muffins) completed the trial. Multivariate analysis of variance of all quality-of-life domains yielded an insignificant treatment × time interaction (F46,122 = 0.92, P = 0.62) but a significant time main effect (P <.0001). Repeated-measures analyses of covariance controlling for body mass index showed no significant group × time interaction nor time nor group differences on all quality-of-life domains and hot flash measures except severity. Hot flashes were less severe with flaxseed (P = 0.001) compared to placebo; however, the group × by time interaction was not significant. Phytoestrogen excretion analysis showed treatment group exposure as allocated and no contamination.

Conclusion: Neither dietary flaxseed nor soy flour significantly affected menopause-specific quality of life or hot flash symptoms in this study.

This three-arm, intention-to-treat randomized, controlled trial of soy and flaxseed muffins versus placebo wheat muffins demonstrated no difference in treatment × time analysis of a menopause-specific quality of life measure or hot flash frequency or severity assessments over 16 weeks.

From the 1Department of Family Medicine, University of Calgary, Calgary, Alberta, Canada; Departments of 2Family & Community Medicine, 3Nutritional Sciences, and 4Public Health Sciences, University of Toronto, Toronto, Ontario, Canada; and 5Clinical Epidemiology, Sunnybrook and Women's College Health Science Centre, Toronto, Ontario, Canada. Dr. Szalai is deceased. Dr. Hilditch is retired.

Received June 29, 2005; revised and accepted October 12, 2005.

Funded by Canadian Institutes of Health Research.

Address correspondence to: Jacqueline E. Lewis, MD, Primary Care Research and Development Group, 1635, 1632-14th Avenue NW, Calgary, Alberta, Canada T2N 1M7. E-mail:

©2006The North American Menopause Society