Dietary Carbohydrate Type and Fat Saturation Independently Regulate Hepatic Cholesterol and LDL Metabolism in Guinea Pigs

Abstract

The interactive effects of dietary fat saturation and carbohydrate (CHO) type on hepatic cholesterol and lipoprotein metabolism were investigated in guinea pigs. Guinea pigs were fed 50.8 g/100 g CHO and 7.5 g/100 g fat. The type of CHO was either sucrose or starch. The fat source was a mixture either high in lauric/myristic (SFA), oleic (MUFA), or linoleic (PUFA) acids. SFA intake resulted in a 50% higher plasma cholesterol and apo B concentrations compared with MUFA or PUFA intake ( P < 0.001). Guinea pigs from the sucrose groups had 20% higher plasma cholesterol and apo B concentrations than those from the starch group ( P < 0.01). Plasma triacylglycerol (TAG) concentrations were highest in animals fed starch and SFA. However, guinea pigs fed starch with MUFA or PUFA had lower plasma TAG than those fed sucrose with the same type of fat ( P < 0.05). Animals fed starch diets had higher concentrations of hepatic free cholesterol (FC) than those fed sucrose. Hepatic acyl CoA:cholesterol acyltransferase (ACAT) activity was higher in guinea pigs fed starch and SFA diets in agreement with higher concentrations of hepatic FC observed in these animals. 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity was higher in guinea pigs fed sucrose and animals fed SFA with starch had the lowest reductase activity ( P< 0.01). Animals fed starch with MUFA or PUFA had 100% higher hepatic LDL receptor number (B max) compared with animals fed SFA. An interactive effect between CHO type and fat saturation was found because animals fed starch with MUFA had the highest and animals fed starch with SFA had the lowest LDL receptor number ( P < 0.02). These studies demonstrate that SFA and sucrose intake independently increase plasma cholesterol and TAG levels by specific alterations in hepatic cholesterol metabolism associated with production and catabolism of lipoproteins. In addition, there was a beneficial effect between MUFA, PUFA, and starch because intake of these nutrients resulted in lower plasma cholesterol and TAG levels in guinea pigs.