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Consumption of soy isoflavones does not affect plasma total homocysteine or asymmetric dimethylarginine concentrations in healthy postmenopausal women
Journal of Nutrition, January 2006, 136(1):100-5
Postmenopausal women have a higher risk for cardiovascular disease because of low estrogen levels. Isoflavones, which are weak estrogens, could reduce this risk. This study investigated the effects of isoflavones on the atherogenic amino acids homocysteine and asymmetric dimethylarginine in postmenopausal women. The participating women took fruit cereal bars with or without soy isoflavones during a period of 8 weeks. The researchers found that isoflavone supplementation did not affect plasma total homocysteine or asymmetric dimethylarginine. The study concluded that the overall health effects of isoflavone supplementation in healthy postmenopausal women are questionable.
Factors affecting the bioavailability of soy isoflavones in humans after ingestion of physiologically relevant levels from different soy foods
Journal of Nutrition, 2006 January, 136(1):45-51
Soybeans have many health benefits but the exact role of soy isoflavones is still controversial. The bioavailability and metabolism of isoflavones and the effect of gender is still not well established. This study investigated the effect of gender, type of soyfood (soy milk, tempeh and textured soy protein) and food matrix on the bioavailability of isoflavones. The intake of soyfood corresponded to 0.44 mg isoflavones per kg body weight. The researchers found that women attained higher peak levels of daidzein then men. The highest serum peak levels of isoflavones were obtained with tempeh, whereas consumption of soy milk resulted in the fastest absorption. Only 30 percent of the participants produced equol. There was no influence of gender on equol production.
Soybean isoflavones alter parvalbumin in hippocampus of mid-aged normal female, ovariectomized female and normal male rats
Acta Pharmacologica Sinica, 2006 January, 27(1):59-65
The aim of this study was to investigate the long-term effect of soybean isoflavones on changes in parvalbumin immunoreactivity in the hippocampus in rats. Previous studies have demonstrated that isoflavones improve the cognitive function in female rats. The treatment with soy isoflavones decreased the parvalbumin immunoreactivity and the number of parvalbumin immunoreactive neurons in certain parts (the hippocampal CA1 region and in the dentate gyrus) of the hippocampus, resulting in a possible change in calcium homeostasis. The reduction in the expression of parvalbumin in the hippocampal CA1 region may protect against memory problems during the aging process.
High concordance of daidzein metabolizing phenotypes in individuals measured 1 to 3 years apart
Britisch Journal of Nutrition, 2005 December, 94(6):873-6
Particular gut flora can produce equol and O-desmethylangolensin from the soy isoflavone. The presence of specific metabolites in urine, after consumption of isoflavones, is a marker of the presence a particular gut. About 30 to 50 percent of the population are equol producers and 80 to 90 percent produce O-desmethylangolensin.
The purpose of this study was to see if equol and O-desmethylangolensin producers keep there status over time. The researchers found after a period of 3 years 82 percent of equol producer and 92 of O-desmethylangolensin producers kept their status, indicating the stability of gut flora responsible for the metabolism of soy isoflavones.
Isoflavones and functional foods alter the dominant intestinal microbiota in postmenopausal women.
Journal of Nutrition, 2005 December, 135(12):2786-92
Isoflavones are often recommended to treat menopausal disorders. It is known that the activity of isoflavones depends on the activity and composition of the intestinal bacteria. The purpose of this study was investigate changes in the dominant microbial flora after 2 month supplementation with isoflavones, with and without pro- or prebiotic. They found transient and lasting changes in the diversity of species, for example there was a prolonged bifidogenic effect.
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