CHAMPAIGN, Ill. — A protein in soybeans has the potential to reduce LDL cholesterol (or “bad” cholesterol) and decrease the risk of developing heart disease, according to researchers from the University of Illinois Urbana-Champaign. So far, studies show that soy has the ability to lower cholesterol and regulate lipids in the body. Now, researchers are closely examining two specific soy proteins they think may cause this, glycinin and B-conglycinin. Results show that consuming soy flour rich in B-conglycinin can potentially reduce bad cholesterol levels.
To reach these findings, the team started out by defatting and grounding 19 soybean varieties that contained various concentrations of these proteins. The proportion of glycinin and B-conglycinin ranged from 22 to 60 percent and 22 to 52 percent, respectively. Using a simulation of human digestion validated by previous studies, the team sequentially mixed the flours with fluids and enzymes that mimic the phases of the digestive system.
From this, they were able to reveal 13 bioactive peptides that are derived from glycinin and B-conglycinin. After digestion, scientists tested the peptides for their inhibitory properties toward HMGCR, a protein that controls cholesterol synthesis. They discovered that the properties were two to seven times weaker than simvastatin, one of the most popular drugs prescribed for lowering cholesterol.
They then broke it down further, classifying the soybean varieties by their glycinin and B-conglycinin makeup to measure their ability to inhibit HMGCR. The team ultimately choose five varieties for further study.
“We started with cells that were already exposed to fatty acids to mimic fatty liver disease and tried to understand the role of the digested soy proteins,” says corresponding author Elvira de Mejia, a professor of food science and human nutrition, in a university release.
“We measured several parameters associated with cholesterol and lipid metabolism and various other markers – proteins and enzymes – that positively or negatively affect lipid metabolism.”
In addition to HMGCR, they studied angiopoietin-like 3 (ANGPTL3), which is secreted by the liver and is integral to the metabolism of triglycerides, LDL, and HDL (“good”) cholesterols. Both proteins are known to be present in excess in fatty liver disease. Interestingly, study authors discovered that peptides from three of the digested soybean types successfully reduced ANGPTL3 secretion by 41 to 81 percent in alignment with their glycinin and B-conglycinin composition. They were also able to increase the amount of bad cholesterol absorbed by liver cells by 25 to 92 percent, depending on the same things.
“One of the key risk factors of atherosclerosis is oxidized LDL cholesterol; therefore, we investigated the preventive effects of the soybean digests at eight different concentrations,” de Mejia says. “Each of them reduced the LDL oxidation rate in a dose-dependent manner, inhibiting the formation of both early and late oxidation products associated with the disease.”
This study shows that food science, nutrition, and public health are all tightly linked. The team is now assessing another relationship, studying the anti-inflammatory capacity of soy based on protein content.
The study is published in the journal Antioxidants.