Some effects of a grain-based mash diet on cholesterol metabolism in swine

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.