Effects of Dietary Protein and Soybean Saponins on Plasma Cholesterol Concentration in Chicks

Effects on plasma cholesterol concentration of protein source, protein content and soybean saponins in the diet were investigated in chicks. Soybean protein isolate fortified with methionine (SPI), or casein with arginine, methionine and glycine (CAA) was used as protein source. Seven-day-old Single Comb White Leghorn male chicks were freely fed the experimental diets for 10 days in all trials. Dietary protein source unaffected the plasma total cholesterol when chicks were fed a 18% protein diet without added cholesterol. Supplementation of 1% cholesterol significantly elevated the plasma total cholesterol in chicks fed the CAA diet, but the replacement of CAA with SPI suppressed that elevation. Soybean saponins at most 1% added to the CAA diet containing 18% protein unaffected the plasma total and high density lipoprotein (HDL)cholesterol, irrespective of dietary cholesterol addition. Addition of 2% cholesterol markedly increased the plasma total cholesterol in chicks fed the SPI diet containing 10% protein with the decrease of HDL-cholesterol. A similar result was observed in chicks fed the SPI diet containing 18% protein, but the effect of added cholesterol was less significant. Likewise, chicks given the CAA diet plus 1% cholesterol showed a decrease in both total and HDL-cholesterol in plasma with the increase of dietary protein content from 10% to 42%. These results indicated that the hypocholesterolemic effect of SPI was not attributed to saponins or non-protein portions. Anim. Sci. Technol. (Jpn.) 63 (8): 793-799, 1992.