Plants contain compounds with oestrogen — like action called phytoestrogens. Soy contains daidzin, a potent phytoestrogen, and wheat flour contains less potent enterolactones. We aimed to show in 58 postmenopausal women (age 54, range 30-70 years) with at least 14 hot flushes per week, that their daily diet supplemented with soy flour (n=28) could reduce flushes compared with wheat flour (n=30) over 12 weeks when randomised and double blind. Hot flushes significantly decreased in the soy and wheat flour groups (40% and 25% reduction, respectively <0.001 for both) with a significant rapid response in the soy flour group in 6 weeks (P<0.001) that continued. Menopausal symptom score decreased significantly in both groups (P<0.05). Urinary daidzein excretion confirmed compliance. Vaginal cell maturation, plasma lipids and urinary calcium remained unchanged. Serum FSH decreased and urinary hydroxyproline increased in the wheat flour group.