In a study from the University of Illinois Urbana-Champaign and elsewhere, scientists found a protein in soybeans blocks the production of a liver enzyme involved in the metabolism of triglycerides and low-density lipoprotein.
They found consuming soy flour rich in the protein B-conglycinin may reduce LDL cholesterol levels and lower the risk of metabolic diseases such as atherosclerosis and fatty liver disease.
Scientists have long known of soybeans’ cholesterol-lowering properties and lipid-regulating effects.
In the current study, researchers tested two soy proteins thought to be responsible for these outcomes—glycinin and B-conglycinin—and found the latter to be particularly significant.
The team defatted and ground into flour 19 soybean varieties, each of which contained different proportions of the two proteins.
The proportion of glycinin in these varieties ranged from 22%-60% while the B-conglycinin ratio ranged from 22%-52%.
Using a simulation of the human digestive process validated by other studies, the team mixed the defatted soybean flours with various fluids and enzymes to mimic the oral, gastric, intestinal and colonic phases of digestion.
They found 13 bioactive peptides produced during digestion, most of which came from glycinin and B-conglycinin.
The researchers found that their inhibitory properties were 2-to-7 times less potent than simvastatin, a popular drug used to treat high LDL cholesterol and fat levels in the blood.
After classifying the soybean varieties by their glycinin and B-conglycinin composition and their HMGCR inhibitory properties, the team selected five varieties for further analysis.
They 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.
They measured several parameters associated with cholesterol and lipid metabolism and various other markers—proteins and enzymes—that positively or negatively affect lipid metabolism.
These markers included HMGCR and angiopoietin-like 3, a protein secreted primarily by the liver that is a critical modulator of lipid metabolism.
Although the fatty acids reduced the liver cells’ absorption of LDL cholesterol by more than one-third, the soybean digests reversed this by inhibiting the expression of a protein.
The digests increased the cells’ uptake of LDL by 25%-92%, depending on the soybean variety and its glycinin and B-conglycinin proportions.
The team found higher concentrations of B-conglycinin in the digests correlated with larger reductions in oxidized LDL, esterified cholesterol, triglycerides and HMGCR levels in plasma.
The digested soybeans’ peptides were able to reduce lipid accumulation by 50%-70%. That was comparable to statin, which reduced it by 60%.
If you care about diabetes, please read studies that flaxseed oil is more beneficial than fish oil to people with diabetes, and green tea and coffee could help reduce death risk in diabetes.
For more information about nutrition, please see recent studies that blueberries strongly benefit people with metabolic syndrome, and results showing vitamin D could improve blood pressure in people with diabetes.
The study was conducted by Elvira de Mejia et al and published in the journal Antioxidants.
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