Soybean Protein Blocks LDL Cholesterol Production, Reducing Risks of Metabolic Diseases

A protein found in soybeans blocks the production of a liver enzyme that involves the metabolism of triglycerides and low-density lipoprotein (LDL), results of a study published in Antioxidants showed.

Consuming soy flour that is rich in B-conglycinin could potentially reduce LDL cholesterol levels and lower the risk of metabolic diseases, such as atherosclerosis and fatty liver disease, investigators said.

“As we hypothesized, soybeans' effects on cholesterol metabolism are not only associated with their protein concentrations and composition but also with the peptides embedded in them that are released during gastrointestinal digestion,” Elvira de Mejia, PhD, a professor of food science and human nutrition at the University of Illinois Urbana-Champaign, said in a statement.

Investigators evaluated 2 soy proteins, B-conglycinin and glycinin, to see if they had any cholesterol-lowering and lipid-regulating properties. They defatted and ground 19 soybean flour varieties containing differing proportions of the 2 proteins.

Investigators mixed the defatted soybean flours with various enzymes and fluids that were used to mimic the colonic, gastric, intestinal, and oral, phases of digestion.

There were 13 bioactive peptides produced during digestion, which mainly came from the 2 soybean enzymes studied.

When evaluating the digested materials’ capacity to inhibit the activity of HMGCR, a protein that controls the rate of cholesterol synthesis, investigators found that their inhibitory properties were 2 to 7 times less potent than simvastatin, a drug used to treat high LDL cholesterol and fat levels in the blood.

Investigators selected 5 varieties for further analysis after classifying the soybean varieties by the composition of the 2 proteins and HMGCR inhibitory properties.

“We measured several parameters associated with cholesterol and lipid metabolism and various other markers, proteins, and enzymes, that positively or negatively affect lipid metabolism,” de Mejia said.

The markers included HMGCR and angiopoietin-like 3, a protein that is secreted by the liver as a modulator of lipid metabolism. Investigators found that the secretion of ANGPTL3 more than tripled after the liver cells were exposed to the fatty acids.

However, they found that the peptides from 3 of the digested soybean varieties reduced ANGPTL3 secretion by 41% to 81%, which correlated with their glycinin and B-conglycinin ratios.

The fatty acids reduced the liver cells’ absorption of LDL cholesterol by more than one-third, and the soybean digests reversed it by inhibiting the expression of a protein.

Additionally, investigators found that greater concentrations of B-conglycinin in the digestion correlated with larger reductions in oxidized LDL, esterified cholesterol, triglycerides, and HMGCR levels in the plasma.

“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 said. “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.”

Investigators also noted that the reduction was comparable to statins.

Reference

A soybean protein blocks LDL cholesterol production, reducing risks of metabolic diseases. Science Daily. News release. January 23, 2023. Accessed January 25, 2023. https://www.sciencedaily.com/releases/2023/01/230123123237.htm