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

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 x time interaction (F-46,F-122 = 0.92, P = 0.62) but a significant time main effect (P < 0.0001). Repeated-measures analyses of covariance controlling for body mass index showed no significant group x 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 with placebo; however, the group x 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.