Prostate cancer is an important and increasing public health problem. It is the second most common cancer in men after lung cancer, and accounts for 10% of all male cancer-related deaths. Within the last three decades. prostate cancer incidence in Scotland has more than doubled, with 2335 cases of Prostate cancer diagnosed in 2002 . The relatively low risk of prostate cancer in Asian populations compared with Western countries, suggests that dietary factors may influence the prevalence of and mortality from this disease . Of special interest is the group of plant-derived nutrients called phyto-oestrogens. in particular isoflavones (genistein, daidzein and equol) and lignans (enterolactone and enterodiol).
Isoflavones are found mainly in soybeans and soy products, foods that are consumed in far greater amounts by populations in Asia compared with those in Western countries . In Western countries, soy foods tend to be eaten most frequently by vegetarians and vegans . Isoflavone precursors are metabolised by the gut microflora to give rise to compounds such as daidzein, genistein and equol . Another group of phyto-oestrogens are the lignans; they are derived from the plant precursors matairesinol and secoisolariresinol which are present in a wide variety of plant foods, including linseed, legumes, cereals, fruits and vegetables. These plant precursors are metabolised by gut microflora into the lignans enterolactone and enterodiol.
The biological properties of phyto-oestrogens include antiviral, antiangiogenic and amioxidam properties Phyto-oestrogens possess weak oestrogenic activity, they compete with oestradiol in binding to the nuclear oestrogen receptor and also stimulate the synthesis of sex hormone-binding globulin, which in turn mediates the plasma levels of testosterone on which the growth, develop¬ment, maintenance and function of the prostate gland is dependent. In addition, phyto-oestrogens can inhibit steroid-metabolising enzymes, including 5α-reductase and aromatase. and also the cell signalling apparatus by the inhibition of tyrosine-specific protein kinases .
Several epidemiological studies support the role of phyto-oestrogens and soy foods in reducing cancer risk However, this evidence is limited, in particular for prostate cancer with only a few studies examining this association usually in populations with high isoflavone/soy food consumption.
This study by Heald et al describes a population-based case-control study of diet, inherited susceptibility and prostate cancer undertaken in the lowlands and central belt of Scotland to investigate the effect of phyto-oestrogen intake and serum concentrations on prostate cancer risk. A total of 433 cases and 483 controls aged 50-74 years were asked to complete a validated FFQ and provide a non-fasting blood sample. Multivariate logistic regression analysis found significant inverse associations with increased serum concentrations of enterolactone and with the consumption of soy foods. However, no significant associations were observed for isoflavone intake or serum genistein, daidzein and cquol.
This study supports the hypotheses that soy foods and enterolactone metabolised from dietary lignans protect against prostate cancer in older Scottish men.
Heald et al 2008 Phyto-oestrogens and risks of prostate cancer in Scottish men. British Journal of Nutrition vol 98, 388-396

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