Subscribe to a FREE Supplement Research Update newsletter. Twice a month we email a brief abstract of several studies on various supplements and natural medicine topics, including isoflavone research and their practical interpretation by Ray-Sahelian, M.D.

Common isoflavones
Of all common plant foods, soybeans appear to have by far the highest concentrations of isoflavones, specifically the soy isoflavones daidzein, genistein, and glycitein. Genistein is one of the best known and studied isoflavones. In addition to soy, isoflavones are found in a number of plants, including raisins and currants.

Mechanism of action of isoflavones
Data from epidemiological reports and laboratories have shown that isoflavones have multi-biological and pharmacological effects in animals and humans. These include estrogenic and antiestrogenic effects, influencing cell signalling conduction, as well as cell growth and death. Isoflavones also regulate gene transcription, modulate transcription factors, act as antioxidants, as well as alter some enzyme activities.

Potential health benefits of isoflavones
Isoflavones are proposed to have health benefits in a variety of human conditions, including coronary heart disease, menopause, osteoporosis, and cyclic mastalgia (monthly breast pain). Many isoflavones have estrogen-like properties and, because of a favorable side-effect profile, may be ideal alternatives to hormone replacement therapy with respect to cardiovascular benefits. Increased isoflavone intake affects estrogen metabolism by altering the steroid hormone concentrations and menstrual cycle length, thereby demonstrating a potential to reduce the risk for breast carcinoma.

Estrogen-Like compounds in Plants and breast cancer
Research in monkeys suggests that the natural plant estrogens found in soy - called isoflavones - do not increase breast cancer risk in postmenopausal women. In fact, they may provide a protective effect. Even at high doses, there was no evidence that isoflavones stimulate cell growth or other markers for cancer risk in breast tissue. Women who have higher levels of estrogen hormone may actually gain a protective effect from higher doses of soy isoflavones. Population studies show women who consume diets high in soy generally have lower rates of breast cancer. You can consume isoflavones from soy, other plants, or take a supplement. It is very difficult to estimate a good amount to take as a supplement since no long term human trials are available.

Isoflavones and heart health
Pasta naturally enriched with isoflavone aglycons from soy germ reduces serum lipids and improves markers of cardiovascular risk.
J Nutr. 2007 Oct. Clinica di Gastroenterologia ed Epatologia, Università degli Studi di Perugia, Perugia, Italy 06100.
The aim of this study was to compare a novel soy germ pasta, naturally enriched in isoflavone aglycons as a result of the manufacturing process, with conventional pasta for effects on serum lipids and other cardiovascular risk markers. In this randomized, controlled, parallel study design of 62 adults with hypercholesterolemia who consumed a Step II diet that included one 80-g serving/d of pasta, we measured serum lipids, high sensitivity C-reactive protein (hsCRP), urinary isoprostanes, and brachial artery flow-mediated vasodilatation at baseline and after 4 and 8 wk. The pasta delivered 33 mg of isoflavones and negligible soy protein and led to a serum isoflavone concentration of 222 +/- 21 nmol/L; 69% of subjects were equol producers. Soy germ pasta reduced serum total and LDL cholesterol more than conventional pasta, representing reductions from baseline of 7% and 8%, respectively. Arterial stiffness and hsCRP decreased and improvements in all the above risk markers were greatest in equol producers. All measures returned to baseline when patients were switched to conventional pasta. In conclusion, pasta naturally enriched with isoflavone aglycons and lacking soy protein had a significant hypocholesterolemic effect beyond a Step II diet and improved other cardiovascular risk markers.

Isoflavones and prostate cancer
Consumption of the estrogen-like isoflavone substances found in soy may reduce the risk of developing early prostate cancer, but isoflavones appear to be associated with advanced disease if prostate cancer does occur.
Isoflavones found in traditional foods that Japanese eat throughout life may be protective against prostate cancer. Dr. Norie Kurahashi and associates from the National Cancer Center, Tokyo, investigated the association between dietary isoflavones and risk of prostate cancer in a study of Japanese men, who generally consume large amounts of soy products and have a low rate of prostate cancer. The study involved some 43,500 men followed from 1995 through 2004. During that time, 307 of them were diagnosed with prostate cancer. Consumption of isoflavones (principally genistein, but also daidzein and soy foods) was associated with a decreased risk of early prostate cancer. Genistein and daidzein, however, were associated with an increased risk of advanced prostate cancer. The protective effect of isoflavones for early prostate cancer was clearest among men over 60 years old, the researchers note, as was the association of isoflavone with an increased risk of advanced prostate cancer. "We suggest that isoflavones delay the progression from latent cancer to clinically significant prostate cancer in Japanese who consume isoflavones regularly throughout life," Kurahashi said. "However, we do not know when or how isoflavones affect latent or (early) prostate cancer development and whether isoflavones can be used in the treatment or...prevention of this cancer."
More studies are needed "to clarify what period in life soy consumption exerts an effect against prostate cancer and what type of prostate cancer it can prevent. Cancer Epidemiology, Biomarkers & Prevention, March 2007.

Isoflavones and weight
A daily serving of soy may help postmenopausal women avoid gaining fat around the middle. In a study of 18 postmenopausal women, those who drank a soy-based shake every day for three months tended to gain less abdominal fat than those who had a milk-based shake. Soy contains compounds called isoflavones that are structurally similar to estrogen and bind to estrogen receptors in fat tissue. So in theory, soy isoflavones could help regulate body fat metabolism. Soy protein may affect abdominal fat distribution. Fertility and Sterility, December 2007.

Inulin and isoflavones
Inulin in the diet or taken as a supplement increases the plasma concentrations of the soybean isoflavones daidzein and genistein. It appears that the absorption of these isoflavones is facilitated by inulin.
 

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