Reduction of serum triglyceride levels by polyunsaturated fat Studies on the mode of action and on very low density lipoprotein composition

Abstract

1.(1) When isocaloric diets high in saturated fat or polyunsaturated fat were alternately fed to hyperlipidaemic and normal men, serum triglyceride was 35% lower (P < 0.001) and serum cholesterol 16% lower (P < 0.001) during the unsaturated fat diet than during saturated fat feeding. A similar response occurred in normal subjects and in patients with primary endogenous hyperglyceridaemia. 2.(2) The magnitude of the reduction of both serum triglyceride and cholesterol due to the unsaturated fat was greatest in subjects with highest baseline levels. 3.(3) The reduction of triglyceride levels during the unsaturated fat period was due mainly to a change in the very low density lipoprotein (VLDL) triglyceride. The fall in cholesterol, however, was due to changes both in VLDL and low density lipoprotein (LDL) cholesterol levels. The triglyceride/cholesterol ratio of VLDL was significantly lowered by the unsaturated fat diet, but the ratio of triglyceride to apoproteins A, B and C was not significantly altered. 4.(4) Postprandial serum triglyceride levels were higher during saturated fat feeding than when unsaturated fat was fed. The difference was due to higher fasting levels, the increment due to alimentary lipaemia being similar during the two diets. 5.(5) There was no change in post-heparin lipolytic activity (PHLA) nor in fractional removal rate of triglyceride as measured by the intravenous fat tolerance test (IVFTT); these indices of triglyceride clearance from plasma suggested that the fall of triglyceride concentration induced by polyunsaturated fat could not be accounted for by enhanced uptake from plasma. 6.(6) Albumin-bound [9, 10-³H]palmitic acid and [1-¹⁴C]linoleic acid were simultaneously infused, and their relative rates of incorporation into very low density lipoprotein triglyceride (VLDL-TG) was measured in six normolipidaemic men. The results suggested that the saturated fatty acid was preferentially incorporated, and may imply that dietary polyunsaturated fat decreases the rate of secretion of VLDL-TG into plasma.