New findings published in the April issue of the Journal of Nutrition suggest soyfoods can play an important role in promoting heart and bone health. The new research was presented at the eighth International Soy Symposium on the role of soy in health promotion and chronic disease prevention and treatment, which was held in Tokyo, November 9-12, 2008.
"Much progress has been made in understanding the health effects of soyfoods since the first Symposium was held in 1994. Each year, the amount of research conducted on the health effects of soy and soybean components continues to impress," says Mark Messina, Ph.D., author of the report and professor of nutrition at Loma Linda University. "The 2008 Symposium in Tokyo provided an ideal venue for researchers in the field to discuss and debate study designs and outcomes. The research presented on soy and heart and bone health showed strong rationale for people to include soy in their diets."
Soy and Heart Health
At the Symposium, the most comprehensive systematic review of the cholesterol-lowering effects of soy was presented. It covered the years 1978 through the present and found that in about two-thirds of the studies judged to be of high or moderate quality, soy protein was shown to significantly reduce total and/or LDL (bad) cholesterol. The meta-analysis that was part of the review showed a net reduction in LDL cholesterol of approximately 5 percent, which is in line with other data. Over time, a 5 percent reduction in LDL cholesterol can reduce heart disease risk from 10 to 15 percent.
"Although modest compared to cholesterol-lowering drugs like statins, the cholesterol-lowering effects of soy protein are similar to those of soluble fiber and certainly relevant from a public health perspective," says Messina. "Integrating a variety of heart-healthy foods - like soy, beans, nuts and certain vegetables - together into a healthy lifestyle are really the best approach to heart health."
When considering all the ways that heart health is potentially improved, soyfoods certainly look impressive, Messina says. In addition to the cholesterol-lowering effects of soy protein, full-fat soyfoods are also good sources of an essential omega-3 fatty acid, which independently lowers risk of heart disease. Plus, because many soyfoods are low in saturated fat and cholesterol free, they can support healthy cholesterol levels when used in place of many of the more traditional sources of protein in the U.S. diet that tend to be high in saturated fat and cholesterol. Furthermore, soyfoods may reduce heart disease risk independent of their effects on cholesterol, through such mechanisms as lowering blood pressure.
"Although no single coronary benefit can be considered to be especially robust, certainly collectively these effects of soyfoods will contribute to a significant reduction in the risk of coronary heart disease," concludes Messina.
Soy and Bone Health
There has been considerable interest in the effects of soy on bone health during the past 10 years, in part because of the low rate of hip fractures among Asians, a population known to have a high rate of soy consumption. Research presented at the Symposium offers hope that soyfoods promote bone health. For example, an Italian randomized clinical trial evaluated the effects of a soy extract on bone mineral density in postmenopausal osteopenic (those with loss of bone mass but not yet with clinical fracture or osteoporosis) women over a three-year period. Women given the soy extract experienced an 8 and 9 percent increase in spinal and hip bone mineral density, respectively, whereas among the women given a placebo, bone mineral density decreased at those sites by approximately 12 and 8 percent, respectively.(1)
In support of these clinical findings are the results of an epidemiologic study presented at the Symposium. The Singapore Chinese Health Study, a prospective cohort of more than 63,000 middle-aged and elderly subjects, examined the relationship between soy intake and risk of hip fracture. Subjects provided information on the intake of soy and other dietary factors at the start of the study and were monitored for approximately 7 years. During the follow-up period, higher soy intake was associated with a one-third reduction in hip fracture risk among postmenopausal women. The results of this study are in agreement with a previously published, prospective study involving women from Shanghai, which also found higher soy intake was associated with an approximate one-third reduction in fracture risk.(2)
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1. Breast safety and efficacy of genistein aglycone for postmenopausal bone loss: a follow-up study. J Clin Endocrinol Metab 2008;93:4787-96.
2. Prospective cohort study of soy food consumption and risk of bone fracture among postmenopausal women. Arch Intern Med 2005;165:1890-5.