The new study, published in the Journal of Clinical Lipidology, suggests that soy protein lowers total cholesterol and non-HDL (non-high-density lipoprotein) cholesterol significantly more than milk protein, in patients with moderately high cholesterol levels.
"Non-HDL cholesterol has been shown to be a somewhat stronger predictor of cardiovascular disease and mortality risk than LDL cholesterol in population studies,"
"The fact that soy protein significantly decreased non-HDL cholesterol levels compared to milk protein in this study is very promising," said Dr. Elaine Krul of Solae, who co-authored of the study.
The research from leading soy supplier Solae, used a relatively insoluble fraction of soy protein isolate from Solae.
Soy protein is protein extracted from the soybean. They are used in a variety of foods including salad dressings, soups, imitation meats, beverages, powders, cheeses, breads, breakfast cereals, and pastas.
The researchers said soy protein and low-fat dairy product consumption have been suggested to have hypocholesterolemic effects, although the responsible mechanisms are poorly understood.
The Food and Drug Administration (FDA) heart health claim for soy protein established in 1999 states that "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease."
Currently, 11 other countries have approved health claims for soy protein's potential to lower blood cholesterol and lower the risk of coronary heart disease. However, recently the European Food Safety Authority (EFSA) issued a negative opinion to a health claim submission linking soy protein and reduced cholesterol – stating that there was not enough evidence of causation to approve a claim in Europe.
The new study evaluated the effects of an insoluble fraction of soy protein and total milk proteins with high calcium content on the fasting lipid profile, and assessed the potential contributions of increased excretion of bile acids and neutral sterols to their lipid-altering effects.
Subjects for this study included men and women 18 to 79 years of age with elevated cholesterol and receiving no lipid altering therapy. Once recruited the participants were asked to follow a new diet throughout the study, which was supplemented by either soy or milk protein.
Both soy protein and milk protein were observed to reduce cholesterol carrying molecules in the bloodstream, as indicated by reductions in total cholesterol, LDL-C, nonhigh-density lipoprotein cholesterol, and apolipoprotein B.
The researchers reported that soy protein reduced all of the markers (except LDL-C) significantly more than milk protein, with soy protein reducing total cholesterol by more than twice that which milk protein did. But observed no significant increases in either group for fecal bile acids or neutral sterols, they said.
The authors said that their results confirmed that soy protein consumption exert a cholesterol reducing effect, and indicated that whilst total milk proteins elicited a less pronounced response they did show a modest cholesterol lowering.
"The results of this study also showed that soy protein lowered non-HDL through a mechanism that does not involve increased bile acid excretion, but some yet to be determined mechanism … Nonetheless, these results are supportive of the heart health claim for soy protein," said Kevin Maki, lead author of the study.
Source: Journal of Clinical Lipidology
Volume 4, Issue 6, Pages 531-542
“Effects of soy protein on lipoprotein lipids and fecal bile acid excretion in men and women with moderate hypercholesterolemia”
Authors: K.C. Maki, D.N. Butteiger, T.M. Rains, A. Lawless, M.S. Reeves, C. Schasteen, E.S. Krul