Effects of a soy protein product on serum and tissue cholesterol concentratins in swine fed high-fat, high-cholesterol diets

Abstract

Hypocholesterolemic effect of a soy protein product was studied in swine fed a high-fat, high-cholesterol diet. In the first experiment, a group of swine were fed 42% butter (by calories) and 1055 mg cholesterol daily, with casein as the source for protein, for 6 weeks and this diet resulted in moderately high serum cholesterol concentrations (219 ± 33 mg/dl). Another group fed the same diet except with soy protein product as the protein source instead of casein showed virtual normocholesterolemia at the end (107 ± 3 mg/dl). Cholesterol balance was studied under non-steady state conditions using methods designed for this purpose. Reflecting the serum cholesterol concentration, the total body cholesterol concentration (excluding CNS) was also significantly lower in soy protein group. However, parameters of cholesterol balance, such as fecal neutral and acidic steroid excretions, dietary cholesterol absorption, and whole body cholesterol synthesis were studied and no differences were demonstrated between the casein- and soy protein-fed swine. The experiment was repeated and in Experiment II virtually the same results were obtained. When swine were given the same high-fat, high-cholesterol diets with 1 2 casein + 1 2 soy protein or casein + soy protein, hypocholesterolemic effects were also observed. Therefore, such action is probably caused principally by soy protein per se rather than simply by replacement of casein by soy protein. Addition of dl-methionine to soy protein containing diet did not alter the hypocholesterolemic effect of soy protein indicating that the effect was not the result of methionine deficiency. In conclusion, we can state that the hypocholesterolemic action of soy protein was clearly demonstrated in swine fed a high-fat, high-cholesterol diet, but that the mechanism of action is yet to be established.