Soy protein alleviates symptoms of fatty liver disease
University of Illinois scientists report that soy protein may significantly reduce fat accumulation and triglycerides in the livers of obese persons. And they’ve discovered why it happens: soy restores partial function of that organ’s key signaling pathway.
“Almost a third of American adults have fatty liver disease, many of them without symptoms. Obesity is a key risk factor for this condition, which can lead to liver failure,” said Hong Chen, a U of I assistant professor of food science and human nutrition.
Fat is metabolized in the liver, and in obese persons, the transport of fat to adipose tissue can slow down to the point that the liver becomes a dumping ground for excess fat, she said.
“When fat accumulates in an organ that’s not supposed to store fat - like the liver, that organ’s vital function can be dangerously compromised,” she noted.
Adding soy protein, in such sources as tofu and soy yogurt, appears to alleviate some of the stress on fatty livers, she said.
Chen’s study compared fat accumulation in the livers of lean and obese rats, which were assigned to either a diet containing casein, a milk-based protein, or a diet containing soy protein isolate, for 17 weeks after weaning. The researchers found that diet had no effect on the liver profiles of lean animals.
Alcoholic Liver Disease (ALD)
More than 15 million people in the U.S. abuse or overuse alcohol. Of these, 90%-100% develop fatty livers.
Fatty liver can occur after drinking moderate or large amounts of alcohol. It can even occur after a short period of heavy drinking (acute alcoholic liver disease).
Genetics plays a role in ALD in two ways. First, it may influence how much alcohol you consume and your likelihood of developing alcoholism. And, it may also affect levels of liver enzymes involved in the breakdown (metabolism) of alcohol.
Other factors that may influence your chances of developing alcoholic fatty liver disease include:
Hepatitis C (which can lead to liver inflammation)
An overload of iron
Obesity
Diet
But obese rats fed soy showed a 20 percent reduction in triglycerides and overall fat accumulation in the liver, leading Chen to believe that soy protein could be used to alleviate the symptoms of fatty liver disease.
Further, the scientists discovered that soy protein isolate partially restored the Wnt/β-catenin signaling pathway, a crucial player in fat metabolism.
“In many obese persons, there’s a sort of traffic problem, and when more fat can make its way out of the liver, there is less pressure on that organ,” she said.
Nonalcoholic fatty liver disease (NAFLD)
Nonalcoholic fatty liver disease is now the most common cause of chronic liver disease in the U.S. Some people with excess fat in the liver simply have what’s called a fatty liver. Although this is not normal, it is not serious if it doesn’t lead to inflammation or damage.
Others have what’s called nonalcoholic steatohepatisis (NASH). Although it is similar to alcoholic liver disease, people with this type of fatty liver disease drink little or no alcohol. NASH can lead to permanent liver damage. The liver may harden and, over time, liver cells may be replaced by scar tissue. This is called cirrhosis. The liver can’t work right and you may develop liver failure, liver cancer, and liver-related death. NASH is one of the leading causes of cirrhosis.
Both types of NAFLD are becoming more common. Up to 20% of adults may have either fatty liver or NASH. And more than 6 million children have one of these conditions, which are most common in Asian and Hispanic children. Recent evidence indicates that NAFLD increases the risk of heart disease in children who are overweight or obese.
The scientists verified the involvement of this pathway by doing in vitro cell culture studies.
Graduate student Dan Zhou found the results especially interesting because of their practical implications. “It’s exciting to think that adding soy protein to their diets might help people who have fatty liver disease,” she said.
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The research will be presented at April’s Experimental Biology meeting. Co-authors are Dan Zhou and Huan Wang of the U of I and Jeremy Davis and William Banz of Southern Illinois University. The study was funded by the Illinois Soybean Association and Solae, Inc.
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Phyllis Picklesimer
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University of Illinois College of Agricultural, Consumer and Environmental Sciences