Soy protein has no hypocholesterolemic action in mice because it does not stimulate fecal steroid excretion in that species.
We compared the effects of dietary soy protein isolate (SPI) and casein on plasma cholesterol level and fecal steroid excretion in rats, mice and hamsters. In rats, compared with casein, SPI significantly stimulated fecal steroid excretion in 9 out of 12 experiments with or without dietary cholesterol, whereas it suppressed plasma cholesterol level in 5 experiments and tended to suppress that, though not significantly, in 4 experiments. In mice, on the contrary, no significant difference was observed between the effects of casein and SPI on either the fecal steroid excretion or plasma cholesterol level in most of 12 experiments in which three different strains were tested. High-molecular-weight fraction of undigested residue of SPI exhibited marked hypocholesterolemic and steroid excretion-stimulating effects in rats and hamsters, whereas it showed only mild effects in mice. The species-dependent difference indicated the existence of inverse correlation between fecal steroid excretion and plasma cholesterol level and supported the view that in species like rat and hamster, but not mice, SPI lowers plasma cholesterol level by stimulating fecal steroid excretion.
Hayashi
S
S
Department of Nutrition, Jikei University School of Medicine, Tokyo, Japan.
Miyazaki
Y
Y
Yamashita
J
J
Nakagawa
M
M
Takizawa
H
H
D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D002364:Caseins / Q000494:pharmacology; D002784:Cholesterol / Q000097:blood*; D006224:Cricetinae; D004044:Dietary Proteins / Q000494:pharmacology; D005243:Feces / Q000737:chemistry; D005260:Female; D008297:Male; D008647:Mesocricetus; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D014674:Plant Proteins, Dietary / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D030262:Soybean Proteins; D013025:Glycine max; D013045:Species Specificity; D013256:Steroids / Q000378:metabolism*
D000924:Anticholesteremic Agents; D002364:Caseins; D004044:Dietary Proteins; D014674:Plant Proteins, Dietary; D030262:Soybean Proteins; D013256:Steroids; D002784:Cholesterol