Dietary Sucrose but not Starch Promotes Protein-Induced Differences in Rates of VLDL Secretion and Plasma Lipid Concentrations in Rats

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Abstract
Casein instead of soybean protein in a low fat, cholesterol-free diet containing sucrose increases both lipid secretion by rat liver and plasma cholesterol concentration. Male rats were studied to determine whether dietary sucrose is a prerequisite for these protein-induced differences of lipid metabolism in vivo. After 6 wk of consuming either casein plus sucrose, soybean protein isolate plus sucrose, casein plus starch or soybean protein isolate plus starch (carbohydrate, 69 g/100 g diet; protein, 20 g/100 g diet) plasma lipids were measured. VLDL degradation was blocked by Triton WR-1339 and rates of lipid secretion were calculated from the observed linear increase in plasma levels with time. Plasma cholesterol concentrations and rates of secretion of VLDL cholesterol and triglycerides were 27, 47 and 34% higher, respectively, in animals fed casein plus sucrose compared with soybean protein plus sucrose. These differences were clearly diminished or absent when starch was the dietary carbohydrate. The data substantiate the finding that dietary sucrose but not dietary starch promotes a casein-induced increase in hepatic cholesterol secretion and thus contributes to casein-induced hypercholesterolemia in rats. On the contrary, differences of triglyceride secretion were not reflected in different plasma lipid concentrations.

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