Effects of the type and level of dietary proteins on plasma lipids, fatty acid profiles, and fecal steroid excretion in rats.

Abstract

The effects of the levels (10, 20, and 30%) of dietary proteins, soybean protein or casein, on various lipid parameters were examined in rats. The plasma and liver cholesterol (CHOL) level tended to decrease with an increasing dietary protein level, in particular when diets contained CHOL. The hypocholesterolemic effect of soybean protein was evident with CHOl-enriched diets. The fecal excretion of acidic but not neutral steroids increased with an increasing protein level and it was higher in rats fed soybean protein than in those fed casein. The ratio of arachidonate to linoleate in plasma and liver phosphatidylcholine tended to elevate accompanying with an increasing dietary protein level, although it was considerably higher in casein than in soybean protein diets. The results indicated that the hypocholesterolemic effect of soybean protein is influenced not only by the level but also by the presence or absence of dietary CHOL. In addition, the degree of the conversion of linoleate to arachidonate also ...