These isoflavones are partial estrogen agonists in cell and animal models, but effects from dietary soy in humans are unclear.
The response to an isoflavone-rich soy food diet was examined in five premenopausal and seven postmenopausal women using transdermal estrogen replacement therapy.
Each subject consumed 50 g textured soy protein containing 60 mg total isoflavones daily for 10-14 d.
The objective of this study was to assess the independent effect of soy relative to common sources of animal protein and soy-derived isoflavones on blood lipids.
Soy-derived isoflavones had no effect on endometrial thickness or the PI of the uterine and cerebral arteries.
CONCLUSION(S): The daily administration of 72 mg of soy-derived isoflavones is no more effective than placebo in reducing hot flushes in postmenopausal women.
To determine the effect of soy-derived isoflavones on hot flushes, endometrial thickness, and the vascular reactivity of uterine and cerebral arteries.
The intake of soy-associated isoflavones increased by 1-95 mg/day and the intake of soy protein increased by 19-60 g/day.
There was no dose-response relation between soy-associated isoflavones and changes in LDL cholesterol (R=-0.33, P=0.14) (Pearson correlation coefficient) or HDL cholesterol (R=-0.07, P=0.76) or their ratio.
To study specifically the effect of soy-associated isoflavones on cholesterol concentrations in well-controlled trials substituting soy protein with dairy or animal protein.
Feeding daily 36 g soy protein with 52 mg soy-associated isoflavones on average decreased low-density lipoprotein (LDL) cholesterol by -0.17+/-0.04 mmol/l (mean+/-s.e.) and increased high-density lipoprotein (HDL) cholesterol by 0.03+/-0.01 mmol/l.
A randomized, double-blind, placebo-controlled study was undertaken to evaluate the concentrations of soy-derived phytoestrogens achieved in breast tissue homogenate, serum, and urine after ingestion of either a soy-based food supplement (n = 9) or a placebo tablet (n = 19) for 5 consecutive evenings before aesthetic breast surgery.
Nowadays, over the counter (OTC) tablet preparations and nutraceuticals with isoflavones extracted from soy and other plants are widespread around the world.
Despite the number of clinical trials performed with isolated isoflavones or with isoflavones included in soy or red clover food products, results did not clarify its efficacy or whether they could be used safely as a treatment as it is claimed.
More information is needed on the biological effects of pure isoflavones and complex mixtures of the various soy isoflavones commonly found in commercial OTC tablet preparations of isoflavones extracted from soy and if the matrix induces changes in the bioability of these compounds.
Once the maximum binding rate of alpha-ERs is determined, the risk of possible tumour cell proliferation by the estrogenic activity of these compounds will be lower and the safety of these OTC tablet preparations of isoflavones extracted from soy, red clover, etc, will be more predictable.
Since the most active isoflavone, which is also the main isoflavone found in soy seeds, is genistein and its derivatives, we decided to compare OTC tablets containing isoflavones extracted from soy, available in the Portuguese market and the isoflavones extracted from soy seeds supplied by the United States Department of Agriculture (USDA) Germplasm bank.
In this study, we employed a transgenic C. elegans model to evaluate the pharmacological effect of the soy-derived isoflavonesgenistein, glycitein and daidzein, on Aβ-initiated toxicity and oxidative stress.
We used a transgenic C. elegans model to evaluate the pharmacological effect of the soy-derived isoflavonesgenistein, glycitein and daidzein, on Aβ-initiated toxicity and oxidative stress.
Apparently, it is the antioxidant activity that contributed to the protective effect by glycitein against Aβ-toxicity (Fig. ) since glycitein is the only soyisoflavone which significantly attenuated the levels of ROS in the C. elegans (Fig. ).
These findings suggest that a specific soyisoflavoneglycitein may suppress Aβ toxicity through combined antioxidative activity and inhibition of Aβ deposition, thus may have therapeutic potential for prevention of Aβ associated neurodegenerative disorders.
The major findings were that consumption of isoflavone-containing soy protein dose-dependently increased insulin responses to the glucose challenge and decreased plasma adiponectin while isoflavone-depleted soy protein decreased body weight and had no effect on plasma adiponectin concentrations.
Soy protein with its isoflavones has previously been shown to improve glycemic control in diabetic postmenopausal women and to improve insulin sensitivity in ovariectomized monkeys.
Further studies are needed to determine the mechanisms involved in these effects of a high soyisoflavone diet and to optimize dietary isoflavone content for maximal health benefits in males.
The second study involved 8 monkeys in a Latin square design that compared the effects of diets with either casein/lactalbumin, soy protein with a high isoflavone concentration, or soy protein that was alcohol-washed to deplete the isoflavones.
Selected isoflavones (genistein, daidzein, formononetin, prunetin, biochanin A, and two synthetic isoflavones) were allowed to interact with soy and whey proteins.
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