Effects of sources of dietary fat and protein on tissue cholesterol

Dietary variables were soy oil, beef tallow, soy protein, and casein. Dietary combinations were soy oil-soy protein, soy-oil casein, beef tallow-soy protein, and beef tallow-casein, and 96 rats were allotted randomly to the four isocaloric diets. [Crystalline cholesterol was added to standardize each diet at 0.2%.] Two randomly selected rats from each dietary group were killed at 0, 7, 9, 11, 13, 15, 18, 22, 30, 36, 42, and 48 days on experiment to determine the effects of sources (plant versus animal) of dietary fat and protein on tissue cholesterol concentrations and on cholesterogenesis in liver and small intestine. Feeding soy oil, a polyunsaturated fat, resulted in lower blood cholesterol concentrations, higher liver cholesterol concentrations, and lower intestinal cholesterogenesis than did feeding beef tallow, a saturated fat. Feeding soy protein, a plant protein, resulted in lower blood and liver cholesterol concentrations and less intestinal cholesterogenesis than did feeding casein, an animal protein. Hepatic cholesterogenesis and intestinal tissue cholesterol levels were not affected significantly by diet. Eight rats killed at day 0 had, on the average, lesser plasma cholesterol concentrations and greater rates of intestinal cholesterogenesis than rats fed experimental diets. Our results demonstrate that the hypocholesterolemic action of soy oil and soy protein fed to rats may be related to decreased intestinal cholesterogenesis. In addition, soy oil, a polyunsaturated fat caused a redistribution of cholesterol from plasma to liver.