Effects of dietary fats on plasma lipids and lipoproteins: an hypothesis for the lipid-lowering effect of unsaturated fatty acids

Abstract

A B S T R A C T Several aspects of the effects of dietary fat on plasma lipids and lipoproteins were investigated in 12 subjects during the long-term feeding of formulas containing 40% of their calories as either saturated or unsaturated fats. The changes in fatty acid composition of plasma lipids, shown previously to occur after prolonged feedings of a dietary fat, required 10-14 days to be complete and were synchronous with the effect of the fat on plasma lipid concentrations. The change in lipid concentration occurred in low but not in high density lipoproteins. The effects on lipid levels of the low density lipoproteins were found to occur with little or no effect on the concentration of the protein moiety of these lipoproteins; as a result, cholesterol-and phospholipid to protein ratios in low density lipoproteins fell during unsaturated fat feeding. The effects of dietary fat on plasma phospholipids were studied in detail: the relative amounts of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and lysophosphatidylcholine were unaffected by the type of dietary fat. However, the molecular species of phosphatidylcholine were markedly affected. More than 90% of the fatty acids at the a-position were saturated during both saturated and unsaturated feedings. In contrast, during unsaturated feedings, linoleate at the ,8-position outnumbered oleate by approximately 4: 1, whereas during saturated feedings these two types of fatty acids were present in nearly equal amounts.This work was presented in part at the Council on Atherosclerosis of the American Heart Association, San Francisco, Calif., 1967, and has been published in abstract form (1).

Oxygen-mediated heterogeneity of apo-low-density lipoprotein.

“…This fatty acid is preferentially unsaturated due to the substrate specificity of the phospholipid acyltransferase (31). Thus, the LDL core contains unsaturated esterified fatty acids in the range of 35-70%, depending on diet (6). In contrast, the corresponding unsaturated fatty acid content of the major VLDL lipid component, triglycerides, is only 7-45% (6).…”

“…Thus, the LDL core contains unsaturated esterified fatty acids in the range of 35-70%, depending on diet (6). In contrast, the corresponding unsaturated fatty acid content of the major VLDL lipid component, triglycerides, is only 7-45% (6). Another factor that may contribute to the more rapid oxidation of LDL compared to VLDL could result from differences in the physical state of the lipid phase, which is considerably less mobile in LDL (32,33).…”

“…LDL contains a large proportion of unsaturated lipids (somewhat variable on diet) (6) and is unique among the serum lipoproteins in its susceptibility for undergoing auto-oxidation in vitro (7)(8)(9). This finding has led some authors to speculate that such auto-oxidation plays a role in atherogenesis (7,10,11).…”

Polyunsaturated fatty acids, hyperlipidemia, and thrombosis.

“…In 1969, Spritz and Mishkel 56 proposed that as dietary polyunsaturated fatty acids became incorporated into plasma lipoproteins, the tortuous geometry of the linoleate molecule would reduce the amount of space available for cholesterol transport, thus lowering the proportions of cholesterol in each LDL particle. The hyperlipidemic patients in this study had decreased cholesterol-to-protein ratios in LDL.…”

“…4 Since 1952, the plasma cholesterol lowering effects of polyunsaturated fat in the human diet have been demonstrated by many investigators. 56 In a typical experiment, a polyunsaturated fat has been substituted for a predominantly saturated fat; i.e., corn oil for cocoa butter. After several weeks of such a feeding, there occurs a remarkable lowering of plasma cholesterol levels which can be promptly reversed if saturated fat is reintroduced into the diet.…”