It is well known that women living in the East are less likely to suffer from menopausal symptoms than those in the West. For instance, while hot flushes affect about 20 p.c. of Chinese and Japanese menopausal women, 70 ” 80 p.c. of European women experience significant problems with this symptom. Some scientists believe that the low rate of menopausal symptoms in the East is related to a high intake of dietary components known as ‘phytoestrogens’. These compounds, found in abundance in soya-based foods and flaxseed, have oestrogen-like actions in the body. Because of their natural hormone-bolstering action, phytoestrogens have become popular as a natural alternative to hormone replacement therapy. However, this month, a review published in the British Medical Journal concluded that phytoestrogens were not effective in treating menopausal symptoms such as hot flushes and osteoporosis. So, is there any good evidence for the supposed health benefits of phytoestrogens, or is their growing popularity more the product of marketing hype than sound science?
At the time of menopause, the production of hormones such as oestrogen declines significantly, and this can lead to a range of symptoms such as hot flushes, night sweats, depression and vaginal dryness. In the long term, menopause is associated with an increased risk of potentially serious medical conditions such as heart disease and osteoporosis (thinning of the bones). The standard medical treatment for menopause is hormone replacement therapy (HRT). However, 80 p.c. of women who start HRT stop it within a year, usually as the result of side-effects. Plus, there is now evidence that HRT does little to protect against heart disease, and there is some doubt about its ability to reduce the risk of bone fracture.
The side-effects associated with HRT and the question marks over its ability to prevent disease have helped to fuel increasing interest in phytoestrogens. In nature, phytoestrogens come in two main forms; isoflavones and lignans. Isoflavones are found most abundantly in soya beans and soya products such as soya milk, tofu (soya bean curd), and soya flour and can also be found in extracts of the herb Red Clover. Lignans are found in flaxseed (linseed) and whole grains. Phytoestrogens have proven oestrogen-like effects in the body, and it is this action which has led to them being recognised as a viable alternative to HRT.
Despite their theoretical benefits, the author of the recent article in the British Medical Journal (BMJ) states there is no evidence to support the idea that for phytoestrogens can combat menopausal symptoms such as hot flushes. The review quotes studies which appeared to show no benefit. Two of these studies showed that neither soya or flaxseed were any better than wheat (the inactive treatment or ‘placebo’) at reducing hot flushes. However, wheat contains some phytoestrogens of its own, casting some doubt over its suitability as an ‘inactive’ treatment in these studies. In fact, a study published last year in the medical journal Menopause found that soya isoflavones helped reduce the frequency and severity hot flushes compared to placebo, and that beneficial effects often occurred within two weeks of starting treatment. Interestingly, this positive study was omitted in the recent BMJ review.
There is some thought that phytoestrogens may help promote bone health, though the BMJ article states that there is little evidence for this. However, one study found that isoflavones extracted from the plant Red Clover led to a significant increase in bone density over a six month period. Other studies have found that a synthetic isoflavone known as ‘ipriflavone’ can increase bone strength in time. While more research may need to be done before we have a clear idea of the effect phytoestrogens have on bone strength, the available evidence suggests considerable potential in this respect.
Another area where phytoestrogens offer some promise is in the protection against heart disease. Several studies show that high soya intake can bring about healthy changes to cholesterol levels which should help protect against heart disease. It is not known quite for sure whether it is soya’s phytoestrogen content or its other constituents such as beneficial fats may be important here. Nevertheless, there is good evidence to support the use of soya-based foods in the diet as a way of reducing heart disease risk.
In addition to reducing the risk of heart disease, soya-based foods seem to help protect against cancer too. For instance, the phytoestrogens in soya are believed to help block some of the cancer-triggering effects of the hormone oestrogen on breast tissue. More than one study has found that the higher the intake of soya products, the lower the risk of breast cancer. Soya has also been linked with protection from prostate cancer in men. One study found that men drinking two or more glasses of soya milk each day had a 70 p.c. reduction in prostate cancer risk compared to men consuming no soya milk at all.