Dietary intake of isoflavones

The mean dietary intake of soy isoflavones in Asian populations consuming soy-based diets ranges from 20-40 mg isoflavones/day, with upper percentile consumer intakes of 70 mg/day (corresponding to around 1 mg/kg body weight). In the six month intervention studies in Western postmenopausal women, the effective dose for improved BMD was around 80-90 mg/day, while in the one year, randomized, double-blind, placebo controlled clinical trial, the effective dose was 54 mg/day. Overall, the dietary recommendation is to consume 50 mg isoflavones/day in combination with standard nutritional requirements for calcium and vitamin D. 

Aral, Y. et al.. Dietary intakes of flavonols, flavones and isoflavones by Japanese women and the inverse correlation between quercetin intake and plasma LDL cholesterol concentration, J. Nutr., 130, 2243, 2000. 

Sagara M, Kanda T, Njelekera M et al. Effects of dietary intake of soy protein and isoflavones on cardiovascular disease risk factors in high risk, middle-aged men in Scotland. J. Am. Coll Nutr. 23, 85-91, 2004. 

It has been shown that in postmenopausal women habitually high intakes of dietary isoflavones are associated with higher bone mineral density (BMD) values at both the spine and hip region (Mei et al, 2001). It is conceivable that an isoflavone-rich diet may help to reverse the state of secondary hyperparathyroidism associated with estrogen withdrawal and hence lower the rate of bone turnover in postmenopausal women, thus reducing the risk of osteoporosis (Valtuena et al, 2003). Phytoestrogens could be used as natural SERMs (Brzezinski and Debi, 1999) and some studies (Setchell, 2001 and refs therein) support such an idea since the molecular targets of... 

Y (1999) Dietary intake and sources of isoflavones among Japanese. iVnlr Cancer. 33 (2) 139 5. 

Setchell KDR, Brown NM, Deal PB et al. Bioavailability, disposition and dose-response effects of soy isoflavones when consumed by healthy women at physiologically typical dietary intakes. J. Nutr. 133, 1027-1035,2003. 

Arai Y, Uehara M, Sato Y, Kimira M, Eboshida A, Adlercreutz H, Watanabe S. 2000. Comparison of isoflavones among dietary intake, plasma concentration and urinary excretion for accurate estimation of phytoestrogen intake. J Epidemiol 10 127-135. 

In the study on colorectal cancer (Table 20.4), a reduced risk was found for increasing intake of anthocyanidins (OR, 0.67 for the highest versus the lowest quintile,p-trend, 0.001), flavonols (OR, 0.64,p-trend < 0.001), flavones (OR, 0.78, p-trend, 0.004), and isoflavones (OR, 0.76, p-trend, 0.001). [Rossi et al., 2006], The estimates did not substantially differ for colon and rectal cancers. After allowance for fruit and vegetable consumption, for dietary fiber, or for micronutrients previously associated to this tumor including vitamin C, the associations with flavonoids did not change by more than 10%. A recent case-control study of 1456 pairs of cases and controls conducted in Sweden confirmed a significant decrease in risk of colorectal cancer for intake of anthocyanidins and flavonols [Theodoratou et al., 2007], but there was no relation for isoflavones and flavones. However, the results on isoflavones and flavones are questionable due to the unusually and generally low intakes of the populations studied. In the Italian population, anthocyanidins were derived mainly from wine, red fruit, and onions, and flavonols from apples or pears, wine, and mixed salads. 

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