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Isoflavones levels in Japanese men and women

Epidemiological studies show that Asians have much lower incidences of prostate and breast cancer than Western people. Because Asians eat more soy foods many scientists believe that consumption of soy foods, such as tofu, soy milk, tempeh and miso, has a protective effect against these types of cancer. But do Asians really eat that much soy foods? Soy foods are a rich source of isoflavones, so determining serum levels of isoflavones will give a good indication of soy food intake.
Morton and co-workers at the University of Wales College of Medicine measured the concentrations of four phytoestrogens (daidzein, genistein, equol and enterolactone) in serum samples obtained from Japanese and British individuals older than 40 years. They found that Japanese individuals had higher serum levels of daidzein, genistein and equol than individuals from United Kingdom. For example Japanese men had serum genistein levels of 493 nmol/L, compared to only 33 nmol/L in British men. They also found that 56% of Japanese men and 38% of Japanese women had high equol levels (> 20 nmol/L), whereas no British men and only 2% British women had high equol levels.

Only individuals older than 40 years, who more likely to consume a traditional Japanese diet, were considered in this study. Unfortunately, the Japanese are slowly abandoning their traditional soy-rich diet in favour of more Westernized foods. This may explain the recent increase in incidence of prostate and breast cancer in Japan.

Source: Phytoestrogen concentrations in serum from Japanese men and women over forty years of age. Journal of Nutrition. 2002 Oct;132(10):3168-71.

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