Soybean resistant protein elevates fecal excretion of cholesterol and bile acids and decreases hepatic cholesterol content in comparison with soybean protein isolate.

The effect of soybean resistant protein (RP) on serum and hepatic cholesterol levels and fecal excretion of steroids was examined. RP decreased cholesterol in the liver, probably due to the stimulated excretion of cholesterol and its metabolites, bile acids. The serum cholesterol level was not different as between RP and other soy-derived proteins.

Evidence for the existence of a soybean resistant protein that captures bile acid and stimulates its fecal excretion.

Feeding HMF, an insoluble "high-molecular-weight fraction" from an industrial enzymatic digest of a soy protein isolate, increased the fecal excretion of bile acid concomitant with increased fecal nitrogen. An amino acid analysis revealed that this increased fecal nitrogen could be explained by an increase in the insoluble protein fraction. This suggests the existence of an indigestible protein or peptide that can be called a "resistant protein" in the feces.