Soy protein may help lower levels

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Certain proteins in soybeans may have cholesterol-lowering effects. Luke Ninno/Getty Images
  • Researchers studied soybeans to determine why they have the ability to lower cholesterol.
  • The scientists studied different levels of two soy proteins: glycinin and beta-conglycinin.
  • They noted that compared to glycinin, soybeans with elevated levels of beta-conglycinin were better able to regulate cholesterol metabolism and inhibit fatty acid oxidation.
  • Eating soybeans with higher levels of beta-conglycinin may help maintain healthy liver and cardiovascular function.

Since heart disease the leading cause of death in the US, researchers are looking for ways to reduce this number. High cholesterol is a risk factor for heart disease, so it’s important to find ways to improve high cholesterol.

Previous studies have shown that eating soy can lower levels of LDL cholesterol, also known as “bad” cholesterol, by as much as 4%.

Researchers at the University of Illinois Urbana-Champaign recently studied different types of soybeans to find out why they can lower LDL cholesterol.

The scientists found one protein in particular to provide benefits and published the study results in the journal Antioxidants.

According to MedlinePlus, cholesterol is a “waxy, fatty substance found in all cells of your body.”

Low-density lipoprotein (LDL) cholesterol is a type that doctors consider “bad” cholesterol. The other cholesterol type is high-density lipoprotein (HDL) cholesterol, which doctors consider “good.”

If LDL cholesterol levels get too high, the buildup can cause plaques to form in the walls of your arteries. This contributes to an increased risk of developing heart disease and stroke.

As Beata Rydyger, registered nutritionist based in Los Angeles and clinical nutrition advisor to Zen Nutrients, noted in an interview with Medical News Today:

Cholesterol imbalances can lead to cardiovascular disease or even neurodegenerative diseases and cancer.

HDL vs. LDL cholesterol

According to the Center for Disease Control and Prevention (CDC), HDL cholesterol “absorbs cholesterol in the blood and carries it back to the liver. The liver then flushes it out of the body.”

Having higher levels of HDL cholesterol is a good thing and can reduce the risk of heart disease and stroke.

The CDC recommends the following cholesterol levels:

  • Total cholesterol: about 150 mg/dL
  • LDL cholesterol: about 100 mg/dL
  • HDL cholesterol: 40 mg/dL and above in men and 50 mg/dL and above in women

The CDC notes that high cholesterol typically has no signs and symptoms, so it’s best to have it checked by a primary care provider during the annual physical.

If someone has high cholesterol, they can treat it with lifestyle changes (diet and exercise) or medications (statins or cholesterol absorption inhibitors).

Previous research has shown the positive effect of eating more soy on people’s cholesterol levels. This new study aimed to understand the mechanism behind the findings.

They suspected that this positive effect could be attributed to two proteins: glycinin and B-conglycinin.

The scientists selected 19 types of soybeans, each with different levels of glycinin and B-conglycinin. The ground soybeans were defatted and studied in gastrointestinal digestion simulation experiments.

In the experiments to mimic food digestion, the defatted soybean meal was mixed with fluids and enzymes from oral, gastric, intestinal and colonic digestion. The researchers performed the simulation with fat cells.

After putting each variety of soybean through this process, the researchers measured how well LDL cholesterol was absorbed.

“We measured several parameters related to cholesterol and lipid metabolism and several other markers – proteins and enzymes – that positively or negatively influence lipid metabolism,” said study co-author Dr. Elvira de Meji, professor of nutrition science at the University of Illinois Urbana-Champaign.

The study’s findings supported the researchers’ hypothesis: The two proteins found in soybeans, glycinin and B-conglycinin, contribute to soybeans’ cholesterol-lowering ability.

“The soybean variety affects protein composition and peptide release under simulated gastrointestinal conditions,” the authors write.

The protein B-conglycinin has particularly good cholesterol-lowering properties. The authors found that the peptide released from this protein “reduced HMGCR expression, the concentration of esterified cholesterol and triglycerides, the release of ANGPTL3, and the production of MDA during LDL oxidation.”

Some soy varieties blocked fatty acid synthesis and caused LDL uptake in the liver. In theory, this could lead to a reduction in fatty liver disease.

“These results indicate that intake of selected soybean varieties could regulate cholesterol and LDL homeostasis and, consequently, promote the prevention of atherosclerotic cardiovascular disease,” the authors write.

Soybeans vs Statins

The researchers also compared the benefits of the soybean meal to Simvastatin, a drug used to treat high cholesterol.

The authors found that peptides from the soybean meal had a similar lipid-reducing property to simvastatin.

“The peptides from the digested soybeans were able to reduce fat accumulation by 50%-70%, which is very important. That was similar to the statin, which reduced it by 60%,” says Dr. de Mejia.

Dr. Jayne Morgan, cardiologist and clinical director of the Covid Task Force at the Piedmont Healthcare Corporation in Atlanta, spoke to MNT about the study.

“Soybeans are known to lower triglycerides, total cholesterol and LDL cholesterol, potentially contributing to a healthier heart profile and becoming part of a heart-healthy lifestyle. This study further complements that,” she said.

Dr. Morgan said she would like to see studies on how soy affects women.

“The effects of soy on estrogen, especially in menopausal women for women’s health, were not addressed, but rather focused on different species and digestive health. I would also like to see information on soy and breast cancer. Again, more studies focused specifically on women,” said Dr. Morgan.

While the researchers tested 19 varieties of soybeans, Rydyger noted that there are more than 2,500 varieties of soybeans. This makes it difficult for people to know what to consume in order to receive benefits.

“They can come in all different colors and sizes, so it’s important to determine whether some varieties are more beneficial for heart health than others,” Rydyger said.

Isabel Vazquez, a registered dietitian at Memorial Hermann in Houston, meanwhile, warned that “eating soy is not a panacea for heart health.”

“I believe in the benefits of a plant-based diet for heart health; that would include eating a variety of plant sources such as oats, nuts and beans,” Ms. Vazquez told MNT.

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