Plasma lipid and lipoprotein cholesterol levels in swine. Modification of protein-induced response by added cholesterol and soy fiber.

Piglets, aged 8 weeks and weighing 12-18 kg, were fed semi-purified casein or soy protein diets, with or without cholesterol and soy hull fiber, for 2 months. In addition to observing the effects of the dietary treatments on growth, the modification of the primary hypocholesterolemic action of soy protein by cholesterol and soy fiber was studied. Pigs fed the soy protein or casein diets grew normally with no difference in weight gain. Plasma triglyceride and phospholipid levels, as well as several plasma metabolic indices examined, were not significantly affected by dietary treatment. However, plasma total cholesterol was higher (but not significantly) in pigs fed casein than in those fed soy protein alone. Cholesterol feeding induced markedly significant (P less than 0.05) hypercholesterolemia with either protein source, compared to feeding the proteins without added cholesterol. Dietary soy fiber fed simultaneously with cholesterol decreased the cholesterol-induced hypercholesterolemia, but the reduction was significantly greater (P less than 0.05) with soy protein than with casein in the diet. Analyses of the lipoprotein cholesterol indicated that LDL cholesterol was much more sensitive to the changes induced by feeding cholesterol and soy fiber than either HDL or VLDL cholesterol. These findings suggest a beneficial role of dietary soy fiber in hypercholesterolemia.