Question

I would appreciate having your views on soy isoflavones supplements for men and women.

Answer

Soy, an excellent source of protein, also contains isoflavones, which are phytoestrogens. Isoflavones are micronutrient substances that, in nonhuman primates, have properties similar to estrogen, including an effect on cholesterol levels and inhibition on low-density lipoprotein oxidation (the oxidation that promotes atherosclerosis). It has been suggested that the lower risk of heart disease among Asian compared to Western populations is due to their high consumption of soybean products.

The American Heart Association made the following very clear statement on this issue regarding cardiovascular prevention (published in the scientific medical journal Circulation, 2000, by Ronald M. Krauss):

In 1995 a meta-analysis evaluated 38 clinical trials investigating the effects on soy protein and serum lipids. The analysis concluded that consumption of soy protein in place of animal protein significantly lowered blood levels of total cholesterol, LDL cholesterol, and triglycerides without affecting HDL cholesterol. These effects were greater in subjects with higher baseline cholesterol levels (generally levels 240 mg/dL). Some of the effects of soy in reducing total and LDL cholesterol may reflect the effects of substituting soy products, which are naturally low in saturated fat and cholesterol for foods that are high in these constituents. More recently, results from double-blind, placebo-controlled trials in mildly hypercholesterolemic individuals have shown that 20 to 50 g of soy protein daily significantly reduces LDL cholesterol. Cholesterol reduction may require the presence of soy isoflavones. Soy is especially rich in the phytoestrogen isoflavones, which have weak estrogenic activity. However, some commercial soy foods (e.g. certain soy protein concentrates) are prepared by ethanol washing, which removes most of the isoflavones and other potentially active soy components.

In October 1999, the FDA approved a health claim that allows food label claims for reduced risk of heart disease on foods that contain 6.25 g of soy protein per serving, assuming 4 servings, or 25 g soy protein intake, daily.

It is not clear whether the estrogen-like activities of isoflavones increase the risk of breast cancer, as they may increase breast secretions and the proliferation of breast epithelium. Thus, there are no specific recommendations regarding the intake of soy protein in the diet or as supplements (other than the one mentioned above). It's reasonable to caution women at increased risk for breast cancer against high soy intake.