Abstract
The aim of the first part of this study was to find out in swine how much fat could be included in a cholesterol-free semi-purified diet without resulting in changes in serum cholesterol levels or hepatic microsomal HMG-CoA reductase activities from those in swine fed a grain-based mash diet. Graded levels of peanut oil from 5 to 40% by calories were included in a casein-carbohydrate-cellulose based diet and effects compared with those in swine fed mash (10% fat) for 2 weeks. Serum cholesterol levels were essentially unaffected by any of the diets. However, in the semipurified diet-fed swine at all levels of dietary fat hepatic microsomal HMG-CoA reductase activities were reduced to values circa 25% of those in the mash-fed swine. This is as great as the reduction from mash levels of activity produced by high fat, high-cholesterol hyperlipidemic diets. The aim of the second part of the study was to find out in terms of whole body cholesterol balance difference in the effects of a cholesterol-free, low-fat (9%) semi-purified diet and a mash diet that might account for the differences in hepatic microsomal HMG-CoA reductase activities. The principal difference proved to be in the fecal output of bile acids (908 ± 86 mg/day on mash vs 292 ± 11 mg/day on a low-fat semi-purified diet). Thus the higher hepatic microsomal HMG-CoA reductase activities in the mash fed swine are presumably in response to the greater loss of steroids. The mixed natural fibers in the grain-based mash diet, as compared to cellulose only in the other, probably accounts for the increased fecal output of bile acids.
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