Study: Any Type of Soy Reduces Cholesterol (dateline November 20, 2001)

In an attempt to rival drug treatments for high cholesterol, researchers have been investigating whether diet modification can substantially alter cholesterol levels and thereby lower heart disease risk. Soy has been touted as a heart-healthy food, but researchers have been uncertain whether all types of soy—those high and low in isoflavones—reduce cholesterol. A new study helps clear up the mystery. Researchers found that all forms of soy significantly reduce cholesterol levels in both men and women and lower systolic blood pressure in men.

Recently, soy foods and products have generated much discussion in the health care industry and among the public. Several studies have shown that soy rich in phytoestrogens—natural chemicals that act as weak estrogen in the body—can help lower heart disease risk and may provide some benefit against diseases such as breast cancer. Isoflavones are one type of phytoestrogen. Examples of isoflavones include genistein and daidzein.

However, researchers have been unsure whether soy products low in isoflavones can also provide those same heart benefits. To investigate, lead researcher Dr. David Jenkins of the University of Toronto and St. Michael's Hospital and colleagues studied 23 men and 18 post-menopausal women with high cholesterol. The participants all followed one of three low-fat diets that each lasted for one month. One diet was high in soy isoflavones, one was low in soy isoflavones, and the third was a protein diet.

Dr. Jenkins and his team found that both soy diets decreased cholesterol levels in both women and men and lowered systolic blood pressure in men. (The systolic measurement is the pressure of the blood flow when the heart beats. It is unclear whether soy has a similar effect on blood pressure in women). The researchers hope their research contributes positively to the continued search for dietary solutions to high cholesterol so that fewer American will have to resort to costly cholesterol drug therapy. They are attempting to build complementary diets of cholesterol-lowering foods that mimic the drugs’ effects.

In addition to heart benefits, foods rich in soy have also been shown to have positive effects against other diseases in small studies. For example, soy isoflavones may help protect against menopausal symptoms and osteoporosis. In fact, the North American Menopause Society suggests soy isoflavones as a natural alternative to hormone replacement therapy to help relieve mild menopausal symptoms. Researchers are also investigating whether soy can reduce breast cancer risk (click here for more information). 

Foods high in soy isoflavones include tempeh, whole soybeans, textured soy protein, soynuts, tofu and soymilk. Foods low in soy isoflavones include soy hot dogs and soy-based ice cream. The following chart by the Indiana Soybean Board provides soy content for certain foods:

Additional Resources and References

• The study, "Effects Of High- and Low-Isoflavone Soyfoods on Blood Lipids, Oxidized LDL, Homocysteine, And Blood Pressure in Hyperlipidemic Men and Women," is published in the August 2002 issue of the American Journal of Clinical Nutrition, http://www.ajcn.org/
• The July 25, 2002 HealthScoutNews report by Amanda Gardner is entitled, "All Soy Lowers Cholesterol."
• To learn more about soy, please visit http://www.imaginis.com/breasthealth/soy.asp
• For more information on the soy isoflavone content of foods, please visit the Indiana Soybean Board website at http://www.soyfoods.com/index.html