Soy & Isoflavones in Human Health

 http://www.naturalproductsmarketplace.com/articles/2010/01/soy--isoflavones-i...

Soy & Isoflavones in Human Health

The soybean and its many derivative products are staple foods in many Asian countries. In addition, it has long been one of the shining stars of the health-food scene. Although commonly used in tofu, soy can be found in many other forms, including meat and dairy analogues. Soy protein is available as a powdered product, and soy and its specialty compounds are offered in dietary supplements.

Soy contains valuable constituents, including protein, isoflavones, saponins and phytosterols. Research indicates some of these constituents may provide some very specific benefits, including cancer prevention, cholesterol reduction, building bone density, mitigating menopausal symptoms and fighting diabetes. 

Soy & Cancer

Soy isoflavones have phytoestrogenic and antioxidant properties. The isoflavone genistein, and possibly daidzein, has been proposed to contribute an important part of soy’s anti-cancer effects. Genistein was tested in a study of human breast cancer cell lines, and was found to inhibit the growth of each of these cancer cells.¹ It seems genistein affects estrogen receptors in such a way as to prevent breast cancer growth.²This estrogen-altering response was also apparent in another study examining the influence of total soy isoflavones in premenopausal women, in which isoflavone consumption delayed menstruation and reduced cholesterol concentrations.³

Furthermore, soy’s anti-cancer effects are not limited to breast cancer. In vitro work in human and animal bladder cancer cell lines, using pure soy isoflavones (genistein, genistin, daidzein and biochanin A) and soy phytochemical concentrate, found both inhibited growth of the human and animal bladder cancer cell lines.⁴ Animal research also demonstrated the ability of genistein, soy phytochemical concentrate and soy protein isolate to inhibit the growth of bladder cancer in vivo, reducing tumor size by 40 percent, 48 percent and 37 percent, respectively, as compared with controls.

That said, there is some conflicting research about genistein and breast cancer. Some research suggests genistein is beneficial, while other research suggests it may actually contribute toward the disease.⁵ Much of the negative research has been primarily in vitro, while in vivo study results have been mixed. For example, in one study, genistein given to rats early in their lives helped reduce the incidence of mammary tumors; however, in research where mice were implanted with human breast cancer cells, genistein seemed to promote the growth of tumors in a similar way to estrogen (estrodiol).⁶

Cholesterol Effects

Research indicates substituting soy protein for animal protein may lead to reductions in plasma cholesterol. A study in postmenopausal women examined the effect of soy products and isoflavones on the blood lipid levels over six months.⁷ The women received 40 g/d of either isolated soy protein containing moderate amounts of isoflavones (ISP56), isolated soy protein containing higher amounts of isoflavones (ISP90), or casein and nonfat dry milk. Both groups consuming the isolated soy protein diets had increased levels of beneficial high-density lipoprotein (HDL). A significant lowering of non-HDL cholesterol was found in the groups consuming either of the isolated soy proteins in comparison to the group consuming casein dry milk protein. The results indicate a low-cholesterol, low-saturated fat diet, combined with soy protein therapy, may be effective in positively changing the ratio of HDL to non-HDL in postmenopausal women with high cholesterol levels.

Although this research is very good, there is even more impressive research regarding soy and cholesterol reduction. A meta-analysis published in The New England Journal of Medicine clearly demonstrated soybean protein containing isoflavones has significant cholesterol-lowering properties.⁸ This meta-analysis examined 38 controlled clinical trials, with an average soy protein intake of 47 g/d. Soy intake was associated with a total cholesterol decrease of 9.3 percent, low-density lipoprotein (LDL) cholesterol decrease of 12.9 percent, and triglyceride decrease of 10.5 percent.

Building Bone Density

A review of interventional trials examining isoflavones and bone in animals and humans suggests including them in the diet results in reduction in bone resorption caused by estrogen deficiency.⁹ One particularly interesting study was conducted at the University of Illinois at Urbana-Champaign involving 66 postmenopausal women who were randomly assigned to one of three dietary treatment groups for 24 weeks.¹⁰ One group consumed 40 g/d of protein from casein and nonfat dry milk. Another group obtained 40 g/d of protein from isolated soy protein containing 1.39 isoflavones per gram of protein (providing a total of 56 mg of isoflavones). The last group consumed 40 g/d of isolated soy protein with 2.25 mg isoflavones per gram of protein (providing a total of 90 mg of isoflavones). Bone density was measured twice during the study. Significant increases occurred in both bone mineral content and density in the soy group that received 90 mg of isoflavones; no effects were seen in the other two groups. The authors of this study pointed out this discovery on the benefits of soy is important for postmenopausal women who cannot or choose not to undergo hormone replacement therapy.

Menopause

To that point, the American College of Obstetricians and Gynecologists (ACOG) recommends soy as well as two other botanicals (black cohosh and St. John’s wort) for management of menopausal symptoms.¹¹ In the case of soy, this is due to the phytoestrogen properties of its isoflavones. The ACOG suggests short-term use of the phytoestrogens in soy may be helpful for relieving vasomotor symptoms (such as hot flashes, flushes and night sweats). This is consistent with other research that has found an association between societies that have a high consumption of soy products and a low incidence of hot flashes during menopause.¹² As a matter of fact, in one double-blind study, 60 g/d of soy protein caused a 33-percent decrease in the number of hot flashes after four weeks, as well as a 45-percent reduction after 12 weeks.¹³ Other research has reported significant reduction in the number of hot flashes associated with soy consumption.¹⁴

Diabetes

In postmenopausal women with type 2 diabetes, treatment with a soy product containing 30 g of soy protein and 132 mg isoflavones daily for 12 weeks seems to lower fasting insulin levels, glycosylated hemoglobin, insulin resistance and LDL cholesterol.¹⁵Preliminary clinical research suggests an extract of a fermented soybean product, touchi, modestly lowers blood glucose, glycosylated hemoglobin and triglycerides in patients with type 2 diabetes.¹⁶ In addition, soy isoflavones may help prevent or treat diabetic nephropathy, a complication of diabetes where the kidneys lose their ability to function properly. The condition is characterized by high protein levels (e.g., albumin) in the urine. Replacing animal protein in the diet with soy protein reduces urinary albumin excretion.^17,18

Safety

Soy protein has undergone a rigorous scientific evaluation and is safe when used appropriately. Soy protein products in doses up to 60 g/d providing up to 185 mg isoflavones have been safely used in studies lasting up to 16 weeks.¹⁹ Likewise, soy extracts containing concentrated isoflavones in doses of 35 to 120 mg/d also seem to be safe when used for up to six months.

Despite soy’s history of safe use, there has been some concern that soy isoflavones might negatively influence infant development—especially male infants. However, this concern appears to be unfounded. In fact, one study published in the Journal of the American Medical Association examined the long-term association between infant exposure to soy formula and health in young adulthood, with an emphasis on reproductive health.²⁰ The subjects in this study included adults, aged 20 to 34 years who, as infants, participated during 1965 to 1978 in controlled feeding studies conducted at the University of Iowa, Iowa City (248 were fed soy formula and 563 were fed cow milk formula during infancy). No statistically significant differences were observed between groups in either women or men for more than 30 outcomes—including pubertal maturation (puberty), menstrual and reproductive history, height and usual weight, and current health. In other words, the consumption of soy formula in infancy was perfectly safe, and had no negative impact on development or health.