CHAMPAIGN, Ill. -- Soy protein used for six months by nutrition scientists
in a low-fat, low-cholesterol diet for 66 postmenopausal women increased
bone-mineral density, providing evidence that a key compound in soy products
-- isoflavones -- could be a substitute for estrogen treatment.
The findings were presented Sept. 16 in Brussels, Belgium, by University of Illinois researchers attending the second International Symposium on The Role of Soy in Preventing and Treating Chronic Disease. Isoflavones act like weak estrogen-like compounds that are thought to have effects on bone and cholesterol metabolism. They also are believed to play a role in low breast-cancer rates among women in Southeast Asia where soy protein is regularly consumed.
"Although this is a relatively short-term study for evaluating changes in bone parameters, the results suggest a potential role for soybean isoflavones in maintaining bone health, particularly in the lumbar spine," said Susan Potter, a professor of nutrition. "Soy isoflavones act like weak estrogens in respect to bone metabolism. Maybe postmenopausal women can use soy products instead of estrogen replacement. Maybe women at-risk for breast cancer can tolerate this better than other estrogens."
Two previous studies by Potter that showed soy protein lowered bad cholesterol levels in men who used a similar diet were cited in the Aug. 3, 1995, issue of the New England Journal of Medicine as evidence of soy protein's health benefits. The new study is the first to focus on postmenopausal women.
Potter's team incorporated 40 grams of isolated soy protein into baked goods and drinks used in the women's daily low-fat, low-cholesterol diets. In addition to a control group, one group ate soy protein with a standard level of 56 milligrams of isoflavones, another had products with 92 milligrams.
The higher level of isoflavones produced significant improvements in the bone densities in the women's lumbar spines -- a key location for assessing osteoporosis, a common disorder of aging women that is marked by a progressive loss of bone tissue because of a loss of bone calcium and protein.
The group that consumed the isolated soy proteins, regardless of isoflavone content, saw the greatest improvement in blood cholesterol profiles.
"The two soybean groups produced a more favorable display [of cholesterol levels], a rapid change in fact, compared to the control group," Potter said. "LDL cholesterol -- the bad cholesterol -- dropped significantly, by about 8 percent. HDL -- the good cholesterol -- increased significantly (by about 4.5 percent). So it appears that soy protein is beneficial in regard to cardiovascular risks even though total cholesterol didn't change significantly."
In Belgium, John W. Erdman Jr., director of the U. of I. Division of Nutritional Sciences, reported Potter's bone-density findings; Potter presented her findings on changes in cholesterol levels. The research was supported by the Illinois Soybean Program Operating Board and Protein Technologies International, which provided the isolated soy protein.