The cholesterol-lowering property of soybeans fed to rats is related to the fasting duration

Numerous factors affect plasma cholesterol and, therefore, represent potent ial interferences with the specific effects of diet on lipid metabolism. Af ter casein intake, serum cholesterol levels depend on many experimental con ditions in rats, such as the type of casein, the presence or absence of cho lesterol in the diet, the age and strain of rat, the diet composition, the nutritional status. The effect of fasting duration on selected parameters w as studied in adult male Wistar rats fed a 20% casein and 1% cholesterol-ba sed diet. No changes were observed in total serum, lipoproteins-B and HDL c holesterol and in triglyceride values after an 8 h-fast compared to non-fas ted animals. A significant decrease was induced in total and lipoproteins-B cholesterol with a 12 h-fast. A prolonged fast resulted in a significant d ecrease in these parameters and in triglycerides and in HDL-cholesterol lev els. Fasted animals fed heated soybean meal instead of casein did not displ ay a marked decrease in serum lipids. It appeared that the fasting effect w as more marked in animals fed casein than in animals fed soybeans. These re sults showed the importance of experimental conditions such as nutritional status of animals when blood samples are taken in studies of the hypocholes terolemic effect of soy protein compared to casein.