Phytoestrogens, which are being increasingly promoted as the "natural" alternative to oestrogen replacement therapy (ERT) are compounds derived from plants, which have oestrogen-like properties. They are found in cereals, legumes and green vegetables. The most investigated are isoflavones found in high concentration in soy bean and soy products.
The fact that Asian women suffer fewer hot flushes compared to women in the Western world has been attributed to their traditional diet rich in phytoestrogens. Epidemiological studies also suggest that cardiovascular disease, osteoporosis and breast cancer - diseases which are influenced by oestrogens - occur less often in populations with a diet high in phytoestrogens. This data is however insufficient for the claim that phytoestrogens are important for the health and wellbeing of postmenopausal women.
In order to exert a biological effect plant oestrogens have to be consumed in large amounts since their biological potency is extremely small compared to oestrogen (more than 1000 times less). And also gut bacteria, antibiotics, bowel disease, alcohol, fat, fibre, and protein content of the diet can affect their absorption.
The results of the few published studies on the effect of phytoestrogens on hot flushes do not show a convincing effect. Hot flushes are however a relatively minor aspect of the plethora of health problems associated with the menopause. The suggestion that phytoestrogen consumption might be associated with a lower risk of cardiovascular disease and of breast cancer is obviously of much greater importance.
Evidence to support a protection against heart disease with phytoestrogen consumption is based on its effect in lowering serum cholesterol, LDL cholesterol and triglyceride concentrations. Decreased atherosclerotic plaque formation has been shown with isoflavone-rich diet in the monkey model whilst direct effects on blood vessel wall have been reported in women. Based on this evidence the US FDA proposed that some soy products carry a label indicating that they may reduce heart disease although there is no hard evidence to support this.