Consuming Isoflavone-Rich Soy Protein Can Help Lower "Hidden" Risk Factors for Heart Disease

BUFFALO, N.Y. -- Blood tests to determine the amount of cholesterol and triglycerides in the bloodstream, which are primary risk factors for heart disease, are nearly always conducted after a 12-hour fast.

Increasingly, however, researchers are interested in levels of cholesterol and other lipids, particularly triglycerides, in the bloodstream after eating, a condition called post-prandial lipemia. Post-prandial lipemia has been shown in cross-sectional studies to be associated with the development of atherosclerosis, independent of fasting lipid concentrations.

Researchers at the University at Buffalo have shown that one way to counter this destructive rise in blood lipids after eating is to include soy products in the diet.

"We have found that consuming 25 grams a day of soy protein high in isoflavones lowers the concentration of triglycerides after a meal and this may help prevent cardiovascular disease," said Peter Horvath, Ph.D., associate professor of nutrition and physiology in UB's School of Public Health and Health Professions and senior author on the study.

Antonio Santo, Ph.D. student and instructor in the UB Department of Exercise and Nutrition Sciences and first author, presented results of the research presented Monday at the Experimental Biology meeting in Washington, D.C.

"A large percentage of the population doesn't show high lipid levels in the fasting state, yet they develop cardiovascular disease, so there must be some other process at work," said Horvath. "Not much of life is spent in the fasting state. We need to understand how people deal with the food they've just eaten in order to understand the true mechanisms of cardiovascular disease.

"We know that eating soy or soy products reduces fasting risk factors, but we know very little about what happens to that risk reduction post-prandial," Horvath added.

To study this effect, Santo, Horvath and colleagues assigned 34 sedentary male volunteers between the ages of 18 and 35 to one of three groups: isoflavone-rich soy, isoflavone-depleted soy and milk protein. Isoflavones are antioxidants found in plants that are known to help protect against heart disease and other chronic conditions. They have also been called phytoestrogens, because they have some estrogenic-like activity.

Participants consumed the supplements daily for 28 days along with their regular diets. At the end of 28 days, researchers drew blood samples from the men in a fasting state, had them drink a 1,000-calorie "shake" to replicate a meal, and then took blood samples again at 30 minutes, and 1, 2, 4 and 6 hours. Samples were assessed for glucose, total cholesterol, HDL, triglycerides and other lipid markers.

No differences were observed in fasting lipid levels after supplementation. However, there were significant differences among the groups, particularly in triglycerides, in the post-prandial samples. After eating, the rise of triglyceride levels over 6 hours averaged 626 milligrams per decaliter (mg/dL) in the milk group; 580.3(mg/dL) in the isoflavone-poor group, and 453.9 (mg/dL) in the isoflavone-rich group.

"People should be eating soy rich in isoflavones, and the less processed the better," said Horvath. "These products can reduce the hidden risk of post-prandial lipemia. It's a good idea even for people who have no cardiovascular risk factors. It's making healthy people healthier."

Additional researchers on the study were Robert Brown, Ph.D., from the Department of Biotechnical and Clinical Laboratory Sciences; Harold Burton, Ph.D., Steven Horvath, Ph.D., Renee Melton, registered dietitian, and Min Wan Hung, master's student, all from the Department of Exercise and Nutrition Sciences; and John Leddy, M.D., from the Department of Orthopaedics.

The study was funded in part by The Solae Co. of St. Louis, Mo.

The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.