These studies were undertaken to investigate the mechanism whereby diet modification alters the plasma concentration of high density lipoprotein (HDL) cholesteryl ester and apoA-I and to determine whether diet-induced alterations in circulating HDL levels are associated with changes in the rate of reverse cholesterol transport. Rates of HDL cholesteryl ester and apoA-I transport were measured in hamsters fed a control low-cholesterol, low-fat diet or the same diet supplemented with soluble fiber (psyllium) or with cholesterol and triglyceride (Western-type diet). The Western-type diet increased the plasma concentration of HDL cholesteryl ester by 46% compared to the control diet and by 86% compared to the psyllium-supplemented diet; nevertheless, the absolute rates of HDL cholesteryl ester transport to the liver were identical in the three groups. Diet-induced alterations in circulating HDL cholesteryl ester levels were due to changes in the rate of HDL cholesteryl ester entry into HDL (whole body HDL cholesteryl ester transport) and not to regulation of HDL cholesteryl ester clearance mechanisms. The Western-type diet increased the plasma concentration of HDL apoA-I by 25% compared to the control diet and by 45% relative to the psyllium-supplemented diet. Diet-induced alterations in plasma HDL apoA-I concentrations were also due entirely to changes in the rate of apoA-I entry into HDL (whole body HDL apoA-I transport). These studies demonstrate that the absolute flux of HDL cholesteryl ester to the liver, which reflects the rate of reverse cholesterol transport, remains constant under conditions in which plasma HDL cholesteryl ester concentrations are altered over a nearly 2-fold range by diet modification.
