Jury Still Out on Soy and Health
Analysis of Nearly 200 Studies Shows Limited Evidence of the Health Benefits of Soy
WebMD News Archive
Aug. 25, 2005 - Soy is widely considered to be something of a medicinal super food, touted as helping to prevent conditions as diverse as heart disease, hot flashes, osteoporosis, kidney disease, Alzheimer's disease, and even cancer.
But a new government-sponsored review of soy research shows little to justify the hype.
An analysis of close to 200 soy studies conducted over the past two decades showed only limited evidence of specific health benefits associated with eating soy products or taking soy supplements.
Eating tofu and other soy-based products was associated with a small reduction in low-density lipoprotein, also known as LDL "bad" cholesterol. And taking soy supplements was found to reduce the frequency of hot flashes in postmenopausal women.
But the analysts concluded that the studies are not convincing enough to recommend including more soy in your diet to lower heart disease risk or treat symptoms associated with menopause.
And the research to date fails to prove a protective benefit from soy against a wide range of other medical conditions, including osteoporosis, kidney disease, Alzheimer's disease, thyroid disease, diabetes, and cancer.
"This report shows us that there is a lot we don't know about soy and that more research is needed to determine if soy has any impact on a number of health conditions," says Carolyn Clancy, MD. Clancy is director of the federal government's Agency for Healthcare Research Quality, which sponsored the researcher.
The LDL Findings
The review of 63 studies examining the impact of soy on cholesterol and triglyceride levels found a 3% reduction in LDL levels among study participants who ate soy products.
But they ate a lot more soy than the average American would consider eating -- equivalent to a pound of tofu or three soy shakes a day.
It is unclear from the studies, says researcher Ethan Balk, MD, if similar reductions in LDL can be achieved by eating less soy. Balk is associate director of the Tufts-New England Medical Center Evidence-based Practice Center, which conducted the analysis.
And the lipid-lowering benefit of 3% is modest at best. The reduction in LDL among people taking cholesterol-targeting statin drugs is in the 10% to 50% range.
The review showed no link between soy consumption and a reduction in blood pressure or an increase in high-density lipoprotein, or HDL "good" cholesterol.
Balk tells WebMD that if soy does help protect against heart disease, the benefits are more likely to be seen at a societal level than among individuals.
"If Americans ate more soy products, it might be reasonable to expect that there would be a decrease in the number of heart attacks and strokes," he says. "But at the individual level we can't really show that."