Comparison of Isoflavones Among Dietary Intake , Plasma Concentration and Urinary Excretion for Accurate Estimation of Phytoestrogen Intake

There is an increasing interest in the biological effects of phytoestrogens because of their chemical structures and molecular weights being similar to those of estrogens 1). They are found in many edible plants 2) and are classified into two main groups, isoflavones and lignans. They occur in plants mainly as glycosides, and the biologically active compounds (aglycones) are produced after hydrolysis and metabolism by intestinal microflora 3). Phytoestrogens have been shown to influence sex hormone metabolism and biological activity 4). They also has anticarcinogenic 5) and antiangiogenic activity 6), and induce intercellular enzymes 7). Furthermore, they are antioxidants and inhibit tumor growth in in vitro studies and animal experiments 8,9). Soybeans are a rich source of isoflavones 10). Japanese consume daily considerable amounts of soybeans and its fermented products 11). Such a high intake of soybean foods suggests to exert a cancer protective effect, especially estrogen-related cancers, such as breast, endometrial, ovarian, prostatic and colon cancer among Japanese 12-14). A number of studies in human have reported high individual variability in isoflavone metabolism. Daidzein and genistein undergo further metabolism by gut flora. Genistein, in sheep, is metabolized primarily to p-ethylphenol. However, p-ethylphenol has not been identified in human urine and plasma . The


INTRODUCTION
There is an increasing interest in the biological effects of phytoestrogens because of their chemical structures and molecular weights being similar to those of estrogens 1).They are found in many edible plants 2) and are classified into two main groups, isoflavones and lignans.They occur in plants mainly as glycosides, and the biologically active compounds (aglycones) are produced after hydrolysis and metabolism by intestinal microflora 3).
Phytoestrogens have been shown to influence sex hormone metabolism and biological activity 4).They also has anticarcinogenic 5) and antiangiogenic activity 6), and induce intercel-lular enzymes 7 Table 1.Intake of nutrients and consumption of foods by food groups by Japanese women.
1Percent of total energy intake. 2 Percent of total protein intake.Table 2. Isoflavone status in Japanese women.

DISCUSSION
Epidemiological studies have shown that the mortality of estrogen dependent cancers among Japanese was lower than that of Caucasian 13,24).Japanese consume a lot of soybean products rich in phytoestrogenic isoflavones.We have previously reported the concentrations of flavonoids and isoflavones in various foods and estimated intakes of isoflavones in 50 Japanese women to be 39.5 mg/day/capita 15).It is necessary to find good biomarkers in epidemiological studies to get information on the possible effects of phytoestrogens in the population.We studied whether the plasma concentration and the urinary excretion of isoflavones could be used as appropriate bio- These data suggested that, among women, diets like Japanese may promote the growth and/or the activity of bacterial populations responsible for equol promotion in the colon.However, there was no significant difference in dietary intake between equol metabolizers and non-metabolizers.Equol metabolizers were significantly lower the plasma daidzein concentration and urinary daidzein and O-DMA excretion.Daidzein would be metabolised to equol by intestinal microflora in equol metabolizers.So, equol metabolizers would be lower the plasma daidzein concentration compared with non-metabolizers and result in the lower urinary excretion of daidzein The dietary intake of isoflavones, daidzein and genistein, had significant correlation with both plasma concentration and urinary excretion.The plasma concentration of genistein showed a better correlation with the dietary intake than the urinary excretion.The plasma concentration of daidzein, however, showed slightly lower correlation coefficient with the dietary intake.Watanabe et al. 31) reported that the half-lives of the plasma daidzein and genistein in men were 5.79 and 8 .36h, respectively.We collected blood in the fasting state, which weakens the relationship with the dietary intake.
The plasma concentration is important for the consideration of the bioavailability of isoflavones in pharmacokinetic studies , and their possible biological effects e.g. on the hormonal system.The measurement of urinary excretion of isoflavone is useful for estimation of total isoflavone intake and recovery of original food isoflavones in urine.We concluded that measurements of both plasma concentration and the urinary excretion of isoflavones are useful tools in future studies on the association of phytoestrogen intake and incidence of cancer.Particularly the plasma TR-FIA assays are useful because of the small amount of plasma needed and the convenient analytical procedures.