Soy protein in the diet or from nutritional supplements has little or no effect on the risk factors for heart disease, according to a new American Heart Association scientific statement published in Circulation: Journal of the American Heart Association.
After analyzing 22 studies, an association committee found that large amounts of soy protein in the diet only reduced low-density lipoproteins (LDL) or “bad cholesterol” 3 percent and had no effect on high-density lipoproteins (HDL), or “good cholesterol”, nor on lipoprotein(a) or blood pressure.
Additionally, analysis of 19 studies showed that soy isoflavones, the bioactive molecules found in soy, had no effect on lowering LDL cholesterol or other lipid risk factors such as triglycerides or HDL cholesterol.
“A big LDL-lowering effect from soy protein or the isoflavones didn’t happen,” said Frank M. Sacks, M.D., professor of nutrition at the Harvard School of Public Health in Boston. “In fact, the isoflavones did not lower LDL nor were there any proven positive biological effects in humans.”
In a statement released in 2000, the committee recommended that it was prudent to add soy protein to a diet low in saturated fat and cholesterol. However, the committee re-evaluated the statement after recent, well-controlled studies were added to the knowledge base.
While the analysis of recent studies didn’t show any specific action of soy protein on heart risk factors, the authors said using soy protein products such as tofu, soy butter, soy nuts or some soy burgers could be beneficial. The reason is the high content of polyunsaturated fats, fiber, vitamins, minerals and a low content of saturated fat that could replace other high-fat proteins in the diet, the researchers noted.
“Soy products may have benefits when replacing other foods such as hamburgers,” Sacks said. “Soy burgers have no cholesterol or saturated fat and have high amounts of fiber.”
The committee also found that soy protein and isoflavones did not lessen vasomotor symptoms such as “hot flashes” due to menopause. The results were mixed with regard to soy’s ability to slow postmenopausal bone loss.
The committee found that the efficacy and safety of soy isoflavones for preventing or treating breast, endometrial and prostate cancer are not established. Evidence of benefit from clinical trials is meager and cautionary with regard to a possible adverse effect, the committee reported.
“There are products in the market touting soy isoflavones and the phytoestrogens for issues related to women’s health such as hot flashes, breast cancer and menopause,” Sacks said. “There is nothing proven in this regard; there is little effect on hot flashes, and the osteoporosis prevention effects are mixed.”
Use of isoflavone supplements are not recommended, the committee said, adding that earlier research that indicated soy protein had clinically favorable effects as compared to other proteins has not been confirmed.
Others preparing the statement for the American Heart Association Nutrition Committee include Alice Lichtenstein, D.Sc.; Linda Van Horn, Ph.D., R.D.; William Harris, Ph.D.; Penny Kris-Etherton, Ph.D. and Mary Winston, Ed.D.