Flavonoids and isoflavones are the anti-oxidant phytochemicals which are most consumed by the Japanese. The Japanese consume a lot of soy products (mainly tofu and miso) which contain a lot of isoflavones. The isoflavone genistein has been shown to have anti-oxidant activity and protects the LDL cholesterol against oxidation. This could explain the relative low mortality of Japanese caused by cardiovascular disease and some cancers. Many studies have already demonstrated that high consumption of fruits and vegetables reduced cancer risk.
The aim of this study was to investigate the relationship of the intake of the phytochemicals flavonols, flavones and isoflavones with blood chemistry data. In total 115 women participated with this study. The dietary intake of three days was recorded and urine and blood samples were taken after that period. Also anthropometric measurements were carried out such as height, weight and blood pressure.
The mean intake of
flavonoids was 17 mg and the mean intake of isoflavones 47 mg. The following phytochemicals were determined in the food: genistein, daidzein, myrcetin, fisetin, quercetin, kaempferol and luteolin.
Quercetin was the most important flavonoids, followed by
kaempferol. Most of the flavonoids came from onion consumption whereas the isoflavones came mainly from tofu consumption.
The study concluded that the intake of flavonoids was inversely related with plasma LDL cholesterol. Intake of other phytochemicals was not correlated with plasma lipid levels. There was also no correlation between green tea consumption and plasma lipids. In thus study, the isoflavones were not correlated with plasma lipids but the anti-oxidant property of isoflavones may contribute to the reduction of LDL cholesterol oxidation and may therefore lower the mortality from coronary hearth disease.
Source: Yusuke Arai et al. Dietary Intakes of Flavonols, Flavones and Isoflavones by Japanese Women and the Inverse Correlation between Quercetin Intake and Plasma LDL Cholesterol Concentration. Journal of Nutrition. 2000;130:2243-2250