The role of dietary polyunsaturated fat in lowering blood cholesterol in man

In 1970, Grundy and Ahrens reviewed the various mechanisms that might explain the hypocholesterolemic effects of polyunsaturated fats. The action of polyunsaturated fat could result from (1) an increase in fecal excretion of neural steroids and/or bile acids, (2) a reduction in cholesterol absorption in the small intestine, (3) a decrease in endogenous cholesterol synthesis, and (4) a redistribution of circulating cholesterol between the plasma and tissue pools. The literature contains evidence both for and against each of these theories. Spritz and Mishkel have also suggested the possibility that polyunsaturated fat may influence lipoprotein structure. In this review, we have assessed the evidence for the various mechanisms of cholesterol lowering in man by polyunsaturated fats and have attempted to integrate information available from previous studies with current knowledge of lipoprotein structure and metabolism. It is not our purpose to propose a single mechanism that will apply to all subjects. Rather, it is our aim to review the existing data for the reader so that he may understand the reasons for conflicting viewpoints and may have a framework to which additional facts may be added as further knowledge evolves.