Lipid metabolism in hypercholesterolemic rats affected by feeding cholesterol-free diets containing different amounts of non-dialyzed soybean protein fraction

Objective We investigated lipid metabolism in hypercholesterolemic rats after replacing casein with different amounts of undialyzed soybean protein fraction. Methods The hypercholesterolemic rats were fed cholesterol-free diets containing 2%, 5%, or 10% undialyzed soybean protein fraction (UDSP) for 4 wk. Results The 5% and 10% UDSP groups had significantly lower plasma cholesterol, triacylglycerol, and low-density lipoprotein cholesterol concentrations than did the other groups (P < 0.05). In addition, significantly higher fecal total steroid excretion was observed in these two groups. However, the different amounts of UDSP did not influence liver lipid, plasma high-density lipoprotein cholesterol, body weight gain, daily food intake, or feeding efficiency. Conclusion These results suggested a dose-dependent reduction in plasma cholesterol when casein was replaced stepwise with UDSP (5% or 10%) as a protein source. The hypocholesterolemic effect might have been due to an increase in total fecal steroid excretion.