University of Illinois scientists report that soy protein may significantly reduce fat accumulation and triglycerides in the livers of obese people. And they've discovered why it happens: soy restores partial function of that organ's key signalling 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.
How the soy works
Fat is metabolised 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 yoghurt, 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.
Adding soy protein to your diet
The researchers found that diet had no effect on the liver profiles of lean animals. But obese rats fed soy showed a 20% 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 signalling 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. 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.
(EurekAlert, April 2012)