Effects of dietary fish protein on serum and liver lipid concentrations in rats and the expression of hepatic genes involved in lipid metabolism.

Dietary proteins influence the lipid metabolism of human subjects and animals. This study evaluated the effects of fish protein on lipid metabolism in rats. Alaska pollock fillets, widely supplied as raw materials of surimi, were used as fish protein. As parameters of lipid metabolism, cholesterol and triacylglycerol concentrations in the serum and liver, the fecal excretion of bile acids, and the hepatic expression of genes encoding proteins involved in lipid homeostasis were examined. Rats fed fish protein showed decreased cholesterol concentrations in the serum and liver, and fecal bile acid and cholesterol concentrations were increased. This was caused by the increased expression of cholesterol 7alpha-hydroxylase (CYP7A1) as the digested fish protein inhibited the absorption of bile acid and cholesterol in the small intestine. In addition, it was found that dietary fish protein affects the farnesoid X receptor/small heterodimer partner-dependent pathway, which is negatively regulated by the decreased reabsorption of bile acid. Furthermore, it increased the binding to the promoter of CYP7A1 through activated liver receptor homologue-1.