Phytoestrogens are a group of plant-derived molecules so named because they possess an oestrogen-like activity. The major interest in Phytoestrogens in the 1990s arose in part as a result of an observation that Japanese menopausal women suffered significantly fewer hot flushes compared with their western counterparts. They also appeared to have a lower incidence of breast cancer, cardiovascular disease and osteoporosis. The low incidence of these conditions was correlated with the very high levels of Phytoestrogens found in the traditional Japanese diet.

Effects of Phytoestrogens on climacteric symptoms
Soy: Although there have been a few studies that they have investigated the effects of soy on the incidence and severity of hot flushes in perimenopausal and postmenopausal women, there have not been any uniformity in the studies and the conclusions are difficult to interpret. Some of the studies have used soy as whole grains on in flour form, while others have utilised isolated soy protein. The results of the studies so far reported are contradictory. Some failed to observe any effects, while others have observed varying degrees of benefit. Soy preparations appear, at best, to nearly halve the incidence of hot flushes, which is somewhat in contrast with the relatively few hot flushes experienced by Japanese women. There are now available on the market, soy preparations in the form of pills or capsules at doses of 50-100mg per day. Again, at best, the preparations reduce the number of hot flushes by half. This is not an obvious improvement on the treatment effects achieved with whole soy and suggest that the effect of these compounds is small. Thus, it would seem that larger studies with large numbers of women experiencing a high incidence of severe hot flushes are needed to resolve the issue of how effective soy is.