Effect of dairy fat and milk product supplementation on plasma lipids and low-density lipoprotein metabolism in the guinea pig.

Abstract

Effects of dairy fat composition on LDL metabolism were measured in male guinea pigs fed 15% (w/w) fat diets, either butterfat (BF) or a synthetic butter-like fat mix (SBF). Dietary groups were: whole milk powder (WM), skim milk powder-SBF (SM/S), casein-SBF (C/S), and skim milk powder-BF (SM/B). A hypocholesterolemic effect was observed in guinea pigs fed the WM (plasma cholesterol, 1.5 mmol/L) diet compared to all other diet groups (3. 1 mmol/L). Hepatic LDL receptor B(max) and K(d) values were not different between WM and SM/B diet groups. Animals fed the WM or SM/B diets had higher HMG-CoA reductase activities than animals fed the SM/S or C/S diets. The results demonstrate that butterfat intake results in a hypercholesterolemic response of plasma and liver; however, the predicted hypercholesterolemic effect of miikfat was not observed with the WM diet compared to the SBF and BF fats. These data suggest that some factor(s) in milk, other than the milkfat itself, negates the hypercholesterolemic effect of dairy fat. Additional experiments evaluated the effects of diet supplemented with whole milk and partially reconstituted milk fractions in guinea pigs fed diets containing 15% (w/w) butter-palm oil (1:1) fat, with or without liquid milk products. Dietary groups were: water (WE), non-processed whole milk (NPWM), re-constituted whole milk (RCWM), buttermilk-enriched skim milk (BMSM), butterserum-enriched skim milk (BSSM), and butteroil-skim milk (BOSM). Plasma total cholesterol (3.0 ± 1.4 versus 2.6 ± 0.1 mmol/L) and hepatic cholesterol (8.1 ± 0.6 versus 9.0 ± 1.2 μmol/g) were not different between WE and milk product treated diets. LDL peak densities and calculated diameters, and hepatic LDL receptor B(max) and K(d) were not different among diets. In summary, potential plasma cholesterol lowering factor(s) associated with whole milk may exist in buttermilk or butterserum but can not be identified; however, a diet supplemented with liquid milk products providing up to 46% of the daily energy intake, with higher total fat (1.4-fold) and dietary cholesterol (2.3-fold) did not increase plasma cholesterol and triacylglycerol levels or alter LDL metabolism in the guinea pig.