Soy Isoflavones are used in the Women’s Formula of the CardioTrim health supplement line.

Isoflavones are polyphenolic compounds that are capable of exerting estrogen-like effects. For this reason, they are classified as phytoestrogens—compounds with estrogenic activity derived from plants. Legumes, particularly soybeans, are the richest sources of isoflavones in the human diet. In soybeans, isoflavones are present as glycosides (bound to a sugar molecule). Fermentation or digestion of soybeans or soy products results in the release of the sugar molecule from the isoflavone glycoside, leaving an isoflavone aglycone. Soy isoflavone glycosides are called genistin, daidzin, and glycitin, while the aglycones are called genistein, daidzein, and glycitein, respectively.

The biological effects of soy isoflavones are strongly influenced by their metabolism, which is dependent on the activity of bacteria that colonize the human intestine. For example, the soy isoflavone daidzein may be metabolized to equol, a metabolite that has greater estrogenic activity than daidzein, and to other metabolites that are less estrogenic. Studies that measure urinary equol excretion after soy consumption indicate that only about 33% of individuals from Western populations metabolize daidzein to equol. Thus, individual differences in the metabolism of isoflavones could have important implications for the biological activities of these phytoestrogens.

Soy isoflavones are known to have weak estrogenic activity. Estrogens are signaling molecules that exert their effects by binding to estrogen receptors within cells. The estrogen-receptor complex interacts with DNA to change the expression of estrogen-responsive genes. Estrogen receptors are present in numerous tissues other than those associated with reproduction, including bone, liver, heart and brain. Soy isoflavones and other phytoestrogens can bind to estrogen receptors, mimicking the effects of estrogen in some tissues and antagonizing (blocking) the effects of estrogen in others. Scientists are interested in the tissue-selective activities of phytoestrogens because anti-estrogenic effects in reproductive tissue could help reduce the risk of hormone associated cancers (breast, uterine and prostate), while estrogenic effects in other tissues could help maintain bone density and improve blood lipid profiles (cholesterol levels). The extent to which soy isoflavones exert estrogenic and anti-estrogenic effects in humans is currently the focus of considerable scientific research.

Although hip fracture rates are generally lower among Asian populations consuming soy foods than among Western populations, it is not yet clear whether increasing soy isoflavone consumption in Western populations helps to prevent osteoporosis. The results of short-term clinical trials (less than three months) assessing the effects of increased soy intake on biochemical markers of bone formation and bone resorption (loss) are inconsistent. While at least three controlled trials in postmenopausal women found that increasing intakes of soy foods or soy protein improved markers of bone resorption and formation, an equal number found no improvement. Controlled trials of longer duration are required to determine whether increased soy intake can actually prevent losses in bone mineral density (BMD) or osteoporotic fracture. Most randomized controlled trials to date have examined the effect of soy protein supplements with or without soy isoflavones on changes in BMD over periods of time ranging from six months to two years. While three studies found that BMD losses were significantly lower in postmenopausal women given soy protein supplements containing isoflavones compared to those given milk protein supplements or soy protein without isoflavones, two other studies found no significant difference in BMD loss when soy protein supplements with isoflavones were compared to soy protein supplements without isoflavones. While there is some evidence that isoflavone-rich diets have bone-sparing effects, it is not known whether increasing isoflavone intake appreciably decreases the risk of osteoporosis.

Breast cancer rates in Asia where average isoflavone intakes from soy foods range from 11-47 mg/day are lower than breast cancer rates in the Western countries where average isoflavone intakes in non-Asian women may be less than 2 mg/day. However, many other hereditary and lifestyle factors could contribute to this difference in breast cancer rates. At least 14 observational studies have assessed the relationship between dietary intakes of isoflavones from soy foods and breast cancer risk. Only one out of four prospective cohort studies (three in Asian populations and one in a U.S. population) found that greater consumption of a soy food was associated with a significant reduction in breast cancer risk. In that nine-year study of more than 21,000 Japanese women, the consumption of miso soup, but not other soy foods, was inversely associated with breast cancer risk. Most retrospective case-control studies have not found that women with higher soy isoflavone intakes were at lower risk of breast cancer, except for women who had higher dietary soy isoflavone intakes during adolescence Two case-control studies, one of Chinese women and one of Asian-American women found that women with higher intakes of soy isoflavones from soy foods during adolescence were significantly less likely to develop breast cancer later in life. Overall, the results of numerous observational studies do not support the idea that high soy isoflavone intakes in adults are protective against breast cancer. Although, limited data suggest that higher intakes of soy foods early in life may decrease the risk of breast cancer in adulthood, more research is needed to confirm these findings.

The effects of increasing soy isoflavone intake on the frequency and severity of hot flashes have been examined in a number of randomized controlled trials. Five out of eight clinical trials in healthy perimenopausal and postmenopausal women found that increasing soy isoflavone intake (34-150 mg/day for 1-6 months) from foods or supplements resulted in modest but significant (10-20%) decreases in the frequency or severity of hot flashes when compared to placebo treatments. In general, soy isoflavones were more effective in those women with the most frequent hot flashes and when given twice daily in a split dose. In contrast, a systematic review of 21 placebo-controlled trials found that hormone replacement therapy reduced the frequency of hot flashes in menopausal women by an average of 77% compared to placebo. Breast cancer survivors in particular may experience more frequent and severe hot flashes related to therapies aimed at preventing breast cancer recurrence. However, the three randomized controlled trials that examined the effects of soy isoflavone supplementation in breast cancer survivors found that soy isoflavone supplementation (90-120 mg/day) was no more effective than a placebo in decreasing the frequency or severity of hot flashes over 1-3 months.

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